Ask Ian: Progressive Twist (Gain Twist) in Small Arms?
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- čas přidán 20. 07. 2022
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From Jamie on Utreon:
"I know naval gatling guns like the 20mm CIWS uses gain twist rifling, but are or were there any commercial or military small arms that used gain twist rifling?"
Yes, there have been some significant uses of progressive (gain) twist rifling on military and civilian small arms. These include:
Colt percussion revolvers (1848, 1849, 1851, 1860, 1861 models)
Custom barrels for Sharps, Stevens, and other rifles by Harry Pope
Carcano Model 1891 rifles and carbines
S&W .460 XVR revolvers
There are certainly others, but those are some of the most significant.
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This format for QnAs is great - I liked watching the full-length, and the quality of the answer was obviously similar, but this is so much easier to go back and reference. Easier to remember that "progressive rifling" was talked about in "progressive rifling", rather than #87 or something
Why not both? "Ask Ian #87 - Progressive twist..."
I preferred the full on long Q and A videos myself
Hopefully, Ian will put these videos in a channel playlist, and we will have the best of both
@@nobody8717 Because numbering the single answers have no practical use, mostly because the number is not inherently tied to the answer as the title would be. Numbering large lists on the other hand is useful because that's the only feasible way to differentiate one list from another, because you cannot really make sufficiently descriptive title to reveal all the questions or answers.
Could not agree more!
One thing to remember is that the bullet is accelerating as it travels through the barrel, so even with a constant rate rifling the rotation of the bullet increases somewhat gradually.
Yes, but... The rate of velocity increase is highest near the chamber and lowest at the muzzle. This can be seen in the velocity per inch of barrel charts. Cut an inch off a 26" barrel and there isn't much change in the velocity cut an inch off a 6" rifle barrel and there is quite a larger change in velocity.
The bullet starts to spin only when it engages rifling.
@@GreenCanoeb its called pressure curve but you are correct
@@GreenCanoeb Sure, that's why I said somewhat 😉
@@wrathmachine7609 So we want the deferential of the function that defines the curve?... 😉
Stuff like this is super interesting to me, I’d like to see more “nerdy mechanical engineering” stuff on small arms throughout history
Definitely.
Weatherby still (or did last I checked) use gain twist in their rifles chambered for their proprietary calibers. Several reloading manuals still specify that the load data used is only safe in a factory barrel or one that uses a similar gain twist pattern.
Also, many muzzleloaders making custom guns today still use gain twist. Accuracy isn’t the big reason, per say, but the ability to use a patched round ball or a conical bullet out of the same rifle. Traditional muzzle loaders typically either are best for one or the other, with a few having middle ground twist rates, which may or may not do all that great with either PRB or conical.
The intuitive part of my brain also says, progressive twist should help cut down on erosion of the initial rifling, thereby extending the life of the barrel. Perhaps not as important in hand guns, but I could potentially see it increasing longevity for expensive barrels for rifles of various calibers.
My first thought about this also, especially on very high velocity rounds.
I don't think it'd have much of an effect as purposely running colder loads in your weapon would, more or less. If longevity is the goal, one could cut their powder load by 2-5%. it's easier on the rifling, right? lol
I'd rather work on developing polymer ammo that would reduce hear transfer.
I had thought the rifling at the muzzle was much more important, because ultimately that was what determined how well it was stabilized after it left the barrel. Hence why, to extend the barrel life of many worn out ww2 surplus rifle barrels, it's common to "counterbore" these and essentially drill out the first inch or two of barreling at the muzzle.
If you did that with a progressive twist barrel, you'd be altering the rate at which the bullet ends up spinning once it exits, assuming the twist rate continues to increase right up until the muzzle (which it may not, I don't know.) But if that is the case b you couldn't do this with a progressive twist barrel.
Granted, it takes a massive amount of use to wear out a barrel like that, so it might be a total non-issue. I'm not a gunsmith so maybe I'm totally wrong about this.
@@VosperCDN I was thinking the opposite. The faster, heavier, in general more powerful around, the more gently you want to start rotating the projectile. If you can ease into let's say shallower depth slower twist rifling, then progressively make it deeper and faster, you spin the Round up with less instantaneous Force applied. Since that Forceis equal between the rifling and the projectile, both are saved from excessive wear or damage. At least that's the theory that's propagating through my head. I'll defer to someone who has either actual experience or entire notebooks of math to justify an alternative position.
Must admit I'm really enjoying this format. Still loving the guns, but this related information running in parallel is fascinating.
With Ian, every day really is a school day.
Gun Jesus is one of my favorite youtubers
That shirt is perfection. A normal person won't notice anything beyond a tropical shirt and never realize it's camo.
I think it was Portugal that had some decidedly tropical shirt camo back in the 70's. At least I saw some surplus billed as Portuguese in the early 80's like that.
Camouflaged camo
@@Earthstar_Review The wave of the future.
The emperor's clothes reversed: the greatest majority sees the shirt but only to the worthy it's invisible
I believe the Milkor grenade launchers use progressive rifling as well, in this case mainly to reduce the shock of spinning up a massive 40mm round.
@@timewave02012 yes they are. There's a little piece inside that has to rotate a certain number of times before it arms. That makes sure it's a safe distance before it can detonate.
@@chemistryofquestionablequa6252 That's a really cool safety mechanism! Never heard of that before.
@@adamtennant4936 it's even cooler if you look up a cutaway view of it.
@@chemistryofquestionablequa6252 I'll get on that!
Imagine a mechanical "pre spin" system that got the whole cartridge turning before firing.
I bet Textron considered it for their NGSW submission before deciding such a design would be too simplistic.
The Textron was a fairly simple and ingenious firearm, it was just different.
I didnt know there was such a thing called gain twist rifling. I still have a lot to learn about guns and thanks to Ian, I have subscribed to this channel.. I’ve been learning a lot!
If you watch enough of his videos, he talks about which guns have gain twist rifling as well 😁
Ever hear of a “squeeze bore”? Check that out too.
With nearly every video here, I learn somethin' new. I've been reading up on guns since I've been a teen, but am no industry professional or high-level enthusiast like Mr. McCollum, so I dig every new fact I take in.
One of the items you mentioned was the effect of the twist on the body of the bullet and you were including or at least from what I heard including the 20 MM in this. Now I will admit that my knowledge is dated with my experience ending 1976 but up to then the 20 MM rounds all had copper alloy rotating bands and the steel body was essentially a bore riding design. The gain twist on these is more from the centrifical fuze of some of the designs which depend on the spin of the projectile to line up the elements of their explosive chain and make the rounds safer to handle. Newer rounds like the 30 MM for the GAU 8 have a nylon composition rotating band. All in all, a fine video as always just I felt I had to point out something I felt needed more clarification.
So the idea is that a projectile would not fuse unless it had sufficiently spun to the desired rate first: and so having that rate reached only at the end of the barrel due to the gain twist would prevent squibs from causing serious problems.
That is, in addition to being unable to initiate the fuse while outside the gun.
@@josephk.4200 Well, spin fused rounds activate some minimum distance downrange from the muzzle, not AT muzzle exit.
In long range competition shooting community, gain twist is some what getting popular, especially in 264cal and 308cal. Many 6.5 CM shooters uses 24-28 inch barrel with twist gain from 1:9 (chamber)to 1:7 (muzzle), claimed more stable grouping and slower throat erosion.
The slower erosion is super interesting. Especially with a round like 6.5 cm that relatively kills barrels.
Saves me saying the same thing. I have no doubt as desired muzzle velocities increase in military small arms gain twist will make a big comeback as it's a cheaper solution than more exotic alloys in barrels.
6.5 CM shooters I suspect on average are a pretty gullible lot to begin with so likely they are more inclined towards marketing hype
Gain twist also reduces gas blowby as the bullet travels down the barrel.
In a regular barrel gas blowby increases as the bullet are "worn" going down the barrel and the very high speed gas going forward of the bullet has a blowtorch effect on the rifleling towards the muzzle reducing barrellife.
Another way of reducing the blowtorch effect is having a little choke in the barrel to increase barrellife. Cut rifled S&L barrels have a slight choke lapped into the barrel in finishing. Some highend hammerforged barrels have have choke. The French FRF2 sniperrifle have barrels with choke to increase barrellife.
@@dgoodman1484 Now in my case could care less about any marketing materials as it was more about the intention. My goal was to go for 1000 yard shot without going to big stuff. Initially I chose the .244 Valkyrie but happened on a really bomb deal for a Ruger Precision Rifle. I think the one gripe I have about the caliber is it seems gun smiths/specialists just can not get their shit straight on the round. It seems recommended barrels, lengths, brand, and so on is more in the sky than ever before. What I found interesting during the plandemic ammo shortage was the few rounds that were available being 6.5 creedmoore, .260 Remington, and .300 Winchester Magnum, and .244 Valkyrie. .260 and .300 I was not aware of but talking with some people those two as well are pretty nice rounds and seemed to be same price about.
That all said the gains were to improve a few things on other popular bullets. Recoil, accuracy, and action were the benefits. Even in the shooting competitions it was taking a lot of wins versus the other rounds used. Enough so it made it to articles and reports. So I do not think it is just hype, but as we probably figured out by now. There are many different calibers and many basically forgotten. So is 6.5 supers special? At least for the moment yes it seems to be pretty good. The military adoption is also pushing market share as well due to production to fill the demand. In my opinion the round that needs to be moved from is the 5.56 but that is not going to happen any time soon. Its design purpose was a NATO requirement and its purpose to tumble not really humane overall.
Another modern gun that uses it is the diy FGC-9 MKii! I don't believe there was any real purpose for using it other than showing what could be done using the diy electro-chemical machining techniques thay were developed, but that seems good enough of a reason to me.
I was going to mention the FGC-9 but you beat me to it. There's not really great advantages to using it, but there aren't really any disadvantages to using it. And as you said, with the ECM rifling there's no extra difficulty in adding it.
I think it's just cool that the most anti gun control gun ever made uses a highly complicated rifling system for the lulz
@@gingergorilla695 it really is just for the lulz 🤣
I think Ivan did see some increase in muzzle velocity, but it wasn't really very significant. Maybe 100 fps on average. Just a cool detail.
@@Tunkkis A 100fps increase with 9mm? That is very significant.
to point: all bullets traveling down a rifle "gain twist" in that they move forward first and it takes a short amount of travel in the barrel to gain that spin from the rifling. Variations in chamber pressure can have effects on how quickly they gain.
On Colt revolvers with gain twist:
I own and sometimes shoot an original '51 Navy revolver with this feature, and have looked into it somewhat. To my understanding, the goal was to achieve decent accuracy with both round ball and much heavier conical bullets. Even today, if you shop for repro muzzleloaders you find that ones optimised for heavy conical projectiles tend not to shoot well with round ball and vice versa. The issue is longer conicals need a higher rifling twist for stability, whereas round ball have such a small rifling engagement area that steep twist rifling can just skip over the bullet instead. There's no cylindrical bullet shank to engage the rifling, only a narrow band of lead touches the bore. So if you try to shoot round ball with a full service charge of powder in a barrel meant for conicals, the rifling may just strip away parts of the bullet instead of spinning it up in a predictable manner. Colt's solution sort of works, there's less force on that narrow engagement area so they shoot well enough (but not super accurate, in my experience) with both bullet types.
That makes sense, I was thinking it might be to compensate for softer lead than we generally use today.
Belted balls might give you the happy medium. Slightly elongated ball with a small full diameter flat.
@@Devin_Stromgren it doesn't get any softer than pure lead, which with perhaps a little bit of tin mixed in is the preferred material for black powder shooting. Severely doubt they had access to something softer back then, modern BP shooters tend to go for the softest bullets they can get.
@@Kaboomf Yes, but the more tin the harder the alloy. I'm pretty sure that even the round balls you can buy today have more tin in them than was standard in, say, 1830.
@@Devin_Stromgren No point in adding more expensive tin than you have to. Enough to make casting easier, no more, since BP shooters specifically want soft bullets. A tiny bit of tin makes the alloy flow better so it fills the mold without wrinkles.
The mostly 3d printed improvised PDW, the FGC-9, uses a homemade barrel with progressive rifling. Most likely to better suit the improvised cast lead ammunition in countries where jacketed bullets are not readily available
The most based gun on the planet.
@@pewpew9193 Less based, more basement.
During development of the M39 and M61 gain twist rifle also showed a slight increases in muzzle velocity over uniform twist rifling. The GAU-12 25mm, and the two 30mms, GAU-8 and M230, also use gain twist rifling. Some people claim gain twist is used for fusing reason, but this is not the case. The Army's M50 series 20mm ammunition for the gain twist M39 and M61 uses the same fuses as the Navy's Mk 100 20mm ammunition for the Mk 12 cannon, which has uniform twist rifling. Also, large artillery, 105mm, 155mm, etc., use uniform twist rifling, and these have much more intricate and complex fuses.
IIRC, Harry Pope (precision barrel maker) was the dean of gain twist rifling. He was doing it in the early 20th century.
I really enjoy this format, I feel you can go deeper into each question. Thank you.
Been absolutely loving this Q and A format!
The only variable depth rifling I have heard of is in large guns where the rifling starts deep and finishes smooth bore. This is to reduce drag by smoothing the driving band into the body of the shell.
In Russia, a lot of civilian rifles start of smooth bore and end with about 100mm of rifling. They’re still considered shotguns because the majority of the barrel is smooth bore, but you still get a bit of spin stabilization at the end.
@@sebastianklaus1483 It is amazing the number of non-optimum designs that exist to get round laws. I would have thought that starting rifled, then smooth would work better, as the bullet would not be going fast when it got to the rifling.
Carcano’s had deeper rifling towards the muzzle to reduce friction.
The German 13.2mm TuFG rifle was a squeeze bore where the muzzle was smaller than the breech by 0.2 mm giving a 13mm projectile.
The Australian Myra Extruder 0.22” long rifle was similar with a 0.17” muzzle.
@@allangibson2408 None of that makes much sense to me.
Rifling getting deeper towards the muzzle is likely to cause gas to escape along the groves.
13.2mm down to 13mm does not seem like a useful squeeze, but it is enough to cause stress in the bullet and barrel.
22 to 17 is a useful squeeze, but I suspect it would distort the bullet in variable ways, destroying accuracy.
@@charlesphillips4575 The 22 Myra Extruder was noted for its accuracy and high penetration (a combination of high velocity (a function of being a squeeze bore and the increased breech pressure) and high sectional density (like the 6.5mm Carcano). Spin stabilising a narrow bullet requires high rotational velocity however. The Myra was noted for punching holes in steel that standard 22’s just bounced off.
The theory behind the increased rifling depth was decreased friction (I didn’t actually say it proved to be a good idea (but neither was the Blish “Lock” on the Thomson Gun).
The 13mm TuFG was capable of punching holes in 20mm armor plate at 200m. The bullet design was copied for the 0.50 Browning Machine Gun so that part worked. Browning didn’t copy the squeeze bore aspect however.
Loving the new Q&A Format
A couple of things:
"Progressive Depth" rifling is a major feature in the barrels for the M-134 Mini-Gun.
These barrels have an amazingly light profile, hence barrel wall thickness. There are usually SIX of them being whirled around, each discharging up to 1000 rounds per minute. The barrel wall thickness at the muzzle has to be one of the thinnest I have ever seen on a firearm with that sort of rate of fire. Looking at the drawings for these barrels, the rifling is DEFINED as "progressive depth"; becoming DEEPER at the muzzle; essentially tapered-depth LANDS; the groove diameter is essentially parallel.
Think about that: reaming a tapered bore and then trying to cut rifling into it. The final cherry on top is that these barrels are also hard-chrome lined.
If you get your sticky paws on a new Mini-Gun barrel in its wrapper and take a peek, it becomes apparent that there is more than one way to form a "taper". The rifling in these beasties is STEPPED; a sort of "digital" taper. with short "ramps" between each step. Put simply, H&R, who made a gazillion of these barrels, used quite conventional barrel-making tools to "approximate a "tapered" bore.
Thus, if a techie / armourer type runs in a set of incremental bore gauges to the depths specified, all will be sweetness and light. Bullets accelerating from a standing start to over 2500 FPS just do not care. Whirling a cage of six barrels around in the breeze / slipstream at 1000 RPM helps to keep them "cool" (ish). I have heard rumors of M-134 barrels with Stellite liners like an M-60 barrel, but there is nothing on the drawings about it, nor have I ever encountered one. Any advances?
As tor gain twist; using ancient barrel rifling tools and machinery, it is relatively easy to do. A conventional single-tooth cutter dragged through the bore and guided mechanically by a "pilot" drum with the progressive-twist track on it will do it all night long. One pass at each index and depth, reset the "tooth" a thou' or so, repeat until you have the desired result. Before the advent of "industrial" scale technology, this was done by HAND, in thousands of tiny workshops all over the USA and Europe.
I suspect the Italians went down this road for a couple of reasons. 6,5mm was, at the time a SERIOUSLY small bore, especially when most of the neighbours were still fielding 9 to 12mm bored antiques. Those, like the Brits, who were already fielding 7.7mm (.303") bore arms were using long, torpedo-shaped bullets with jackets drawn from Cupro-Nickel, which is fairly hard stuff.
The engineers probably noticed early bore "wear" in their prototypes / test-beds and sought a solution. Another factor is the "pressure curve" on firing. The Carcano is a tough little action, but has marginal gas shielding . Furthermore, the brass used in the day was still not as refined in formulation AND processing, as it would become less than a decade later. Launching the bullet relatively "gently" was probably considered a judicious thing. Any throat "wear" due to bullet abrasion / propellant gas erosion could be discounted for longer, because the final bullet spin rate was achieved in the final six inches of the barrel.
Progressive depth rifling was used in the UK 's late WWII 3.7" MkVI AA gun where Colonel Probert reduced the last few inches of the barrel to smooth bore, eliminating the barrel wear that affected the MkIV (they were both using a 4.5" case to push a 3 .7" shell) and improving the ballistic performance.
Never had time to watch the long form Q&A. This "one question per video" format is far more useful. Thanks!
These one-subject Q&A videos are really fantastic!
Love these short and sweet Q+A vids.
I like this format better because I don't always have time to watch for an hour or two or three. Quick, to the point--and long enough to cover the subject in detail.
Thank you.
I really like the single question per video format of the Q&A. Thanks for making this change! 🙂
Ian, please continue to break up the q&a into smaller segments like this. I don't always have the time to watch the full session, and having single topic questions answered like this motivates me more to see what interesting information you've researched, especially if it's something I think I know about. Your content is always a bullseye!
Very large bore weapons, such as larger caliber aircraft systems and artillery pieces, use a separate driving band made of softer material than the casing on their projectiles. The driving band engages with the rifling and provides obturation, rather than the casing. One of the tests we used to perform when proofing these systems was to test for driving band slip.
Whilst the use of driving bands is generally a good system, it tends to encourage gas erosion just forward of the chamber. As a result it means a rifled tube may remain in service in such condition that quite a length of the rifling directly ahead of the chamber has been removed by gas erosion. One of the regular tests done on large bore systems is to measure the depth and length of gas erosion to calculate the effect on stabilisation as a result of the lost rifling.
The level of gas erosion present towards the end of the service life of a large bore rifled tube means a projectile starts to accelerate down the bore for some distance before engaging the rifling, and the sudden engagement at higher velocity makes the driving band slip more on the casing. Thus there is less gyroscopic energy present to stabilise the projectile and you are effectively 'shortening' the rifled tube. Progressive rifling helps to alleviate this by reducing the level of driving band slip.
Modern systems are tending towards smooth bore tubes as these alleviate both problems of gas erosion of rifling and driving band slip.
Ian: "Too high a twist rate can lead to jacket separation"
Me: *stares intensely at Q 8.6 BLK supers with a 1:4 twist barrel*
I remember listening to frank galli of snipershide talk about how he had a 338 lapua that had some radical twist rate because of the mono-copper bullets it was using. Supposedly, the bullet being overspun helped transonic turbulence be overcome and it had to be all copper because the lead being soft and very hot would explode through the jacket. I assume the blackout either gets around this by being slow enough or having monometal bullets.
@@khopkins9632 that's the thing, it does neither
@@charlesfisher3983 Well, it being slower projectile surely helps a lot.
@@randomnobodovsky3692 it's still supersonic. At the advertised twist rate and muzzle velocity (2200 fps], the 8.6 blk is doinb 2.7 million rpm and the jacket is experiencing 1.3 million g. The only thing that can stand up to that are solid bullets. Which 1 damage the barrel and 2 are prohibitively expensive
@@charlesfisher3983 2200fps is 26400 inches per second. With 1/4 twist rate (1 revolution per 4 inches) it's 396000RPM (6600 revolutions per second multiplied by 60). Or is my math wrong?
I'm loving the format of these Ask Ian videos.
Thanks for the new-to-me insights into rifling.
Such great info. I wish more technical experts were as adept as Ian at explaining their field in layman’s terms
The new format is awesome, but I absolutely love the ability to chuck on a hour long Q&A video and just listen along and relax. Please don't completely give up on the longform!
I recommend stringing together several short Q&A videos into a playlist.
Ian really has taught me well. I realized gain twist would be useful to reduce fouling in black powder firearms a few minutes before he got to it.
I love the short form, one question videos, please continue!
Wonderful question :) Thanks for the in depth research and answer Ian
I love this new video format!
I'm learning so much. This content is out of this world.
very interesting. the extended single question Q&A is really nice.
I really like this format better than the longer multiple questions format.
Thanks Ian. I always learn something new in your videos!
Very informative as always. Thanks.
One aspect that was not so much tuched on was the relation between oreassure and heat and the resulting barrelwear. You mentioned it abit with the carrcano. The exccesiv ware can be dealt with by different surface treatments but the issue with heat stays. It should reduce the heat in ex machingun barrels specially with the new high preassure rounds that are beeing procured recently.
So a combination with the polymer casing and gaintwist i think it could really prolong the fieribg cykle. Sthough I supposse it is a more expensive production method.
The depth one is new to me, makes sence. Thank you.
The M242 25mm Bushmaster on the M2/M3 Bradley and the Canadian LAV 6.0/LAV Recce has a gain-twist barrel... we were told on or Gunnery Course that the gain twist barrel was used mainly to reduce initial pressure on firing a round, and to eliminate any rotational damage to the HE fuzes on the HE rounds...
For your files:
Other than a couple of demo sporting guns produced prior to the sPzB 41, rifling development seems to have been done on larger weapons rather than rifles and pistols.
The British 3.7" AA gun Mk VI, actually a 4.5" gun lined down to 3.7", used rifling that disappeared some distance before the muzzle, "Probert" rifling, which smoothed the driving bands down into the shell body, requiring appropriately-designed shells. Velocity increased and with much less barrel stress than a true squeeze bore design. The V-1 really got the attention of the British. The development of SAMs replaced these weapons.
In the mid-90's, there was some work on various rifling twist rates (parabolic, cubic-parabolic) for light AA guns (~30mm-40mm) that changed the barrel pressure curve, from the usual quick rise followed by a decay, to a less quick rise (to ~60%) followed by a roughly level pressure until projectile exit, or a section of a circle, until projectile exit. Apparently, this work also went nowhere, due to smoothbore weapons becoming mature enough, and various SAMs being much more effective than guns. Brassey's "Cannons", by D.F. Allsop, 1995, p38 and 39 are the only 2 pages I've ever seen on this topic.
The implication, AIUI, is that a Weatherby cartridge would then generate ~40,000psi instead of ~65,00psi, generate a noticeably higher muzzle velocity, last much longer, but would have to be a bull barrel design, and maybe even slightly larger in diameter. I see a 2" dia, 26"barrel, as a "No".
There are a lot of jacketed bullets that are suited for the .45 Colt cartridge, that would not stand up to the much higher pressure of the .460 S&W. The gain twist in the .460 would not put as much stress on those bullets. Also, there could be a slight reduction in chamber pressure, but I don't know that for a fact.
Ian mentioned this in the video about the auto mag .357AMP kit. I wonder if progressive rifling would minimise the problems with that cartridge. I live in the UK so all this might as well be "how to engineer a unicorn" but it is sure interesting stuff.
One thing I remember reading about them as a disadvantage is the non constant engraving of the bullet. Imagine the path that is forced into the jacket needing to change shape as it.kove down the barrel.
Hi Ian, could you do a follow up to explain the logic behind straight rifling? As in rifling that literally goes straight down the barrel or nearly so, as seen on some French post-ww2 cannons?
Enjoyed that video, thank you for sharing your knowledge Ian.
This is a really good format for the show.
I didn't even know this was a thing. Learning something new every day, appreciate the video!
Part of the large bore issue is that the circumference is far larger so the outside is being accelerated in it’s rotation far faster than in a small diameter bullet so the stress on the jacket/case join is much larger. Lead bullets for black powder arms suffered similar issues due to the ductility of the lead so the stress was at the lead/steel rifling point so their interpretation was the lead stripping off the skin of the bullet and damaging accuracy and lead fouling the bore. Initially that led to harder lead alloys and then to paper patching. Forsyth dealt with the issue in large bore sporting muzzle loaders by drastically reducing the twist to allow higher speeds from larger charges.
At the end of the day the bullet exits the barrel with the twist rate at the muzzle. As long as it is not damaged then the rate of change of the twist earlier in it’s journey up the barrel has no effect. Gain twist is useful only in limiting the stripping of the bullet lead skin or hard bullet jacket.
Thank you for explaining this Ian.
Thanks for answering! Had no idea it was still used and progressive depth... mind blown. Awesome work Ian!
I could see reasoning the progressive twist rifling on the 460 S&W for exactly the reason Ian noted. Imagine a 180-grain jacketed bullet intended for the 45 ACP handloaded hot in a 460 S&W. I'm sure the velocity would be impressive but at that speed the jacket may have difficulty remaining intact with the lead core.
Speer 200gr hollow point meant for. 45acp would be bad.
For black powder, progressive twist with round bottom grooves and patched round ball increases shot count between cleaning.
Former CIWS tech here. The barrels are surprisingly easy to clean; you'd think there'd be lots of fouling from it's high ROF (4,500 air, 3,000 surface mode). Thanks to the plastic discarding sabot however, that's not the case. The actual heavy tungsten penetrator is 17mm; the plastic jacket petals off very quickly after the projectile leaves the muzzle, due to it's incredibly high velocity.
Let's do the twist
When the pressing screwed up the constant surface speed curve on your LP…
Now let's do it faster
Good question and great answer. Thanks 👍
The one thing I think would make this format of Q&A better than the hour long version in every way would be putting them all into a playlist together. One of the reasons I liked the old long format version is I could treat it as a podcast and listen without having to navigate the CZcams app to find a new video and change it. A playlist of all of these shorter vids would alleviate that issue.
One thing I did notice, because I shoot a lot of both semi-automatic double action revolvers and single action revolvers. Is that on my Super Blackhawk when I inspect recovered bullets, the Leading Edge of the bullet where is engaging the rifling always has skid marks on it where it is engaging and slipping on the beginnings of the rifling. It's an interesting way to show whether or not a particular projectile was fired from a single action revolver or a double action revolver. Because they have a longer cylinder normally, the bullet accelerates much faster before it engages the rifling. In something like a 44 Ruger Super Blackhawk, I have seen test where they have completely removed the barrel and the bullet from a Winchester 240 grain hollow point will exit the cylinder at 1100 ft per second, if you leave just 1 inch of barrel it will be about 100 ft per second less
I think this is something that needs further research.
Enter the 8.6 blackout 1 in 3 twist.
Because the bullet is mostly sub-sonic variants the 1 in 3 does very well, and delivers unheard of accuracy and energy.
If a much faster super-sonic round started with a slow twist rate and ended with something like a very fast 1 in 3. I believe there would be significant improvement similar to 8.6 BO
Great Report .
Thank You .
I legitimately learned some interesting things from this video. Keep up the excellent work.
FYI "Twist" is when one end rotates more than the other. The barrel twists. "Spin" or "rotate" is when both ends turn at the same rate. The bullet "spins", not "twists". However, in a gain twist barrel, the bullet IS forced to twist, which imposes enormous shear stresses on it.
I remembered that Smith and Wesson's X-frame revolvers used the rifling, but forgot that it was limited to the 460s, so I just learned that. Definitely learned about the pre-Peacemaker Colts and the 1891 Carcano.
I was guessing that the rifling becomes more important in chain and Vulcan cannons because the 'twist shock,' as I call it - going from zero to thousands of RPM - could cause the filler in the shells to detonate... but I may be wrong there.
Huh, never knew there was such a thing a progressive depth rifling. You learn something new every day!
Still love the shorter format, Ian!
Ian is phenomenal is his knowledge and comprehensive understanding of what can only be described as his savant-like obsession with firearms and their history in our lifetimes and before. Great for him. Great for us. God bless Ian!
This q&a format is the best ever!! Sorry to ask this of you, but whenever you mention a gun or a bullet, could you please have its picture on the side?
A bit on the physics aspect: The bullet is starting with zero velocity and accelerating from there. The twist just forces a specific ratio between the linear velocity and rotational velocity. In a constant twist barrel it forces the rotational velocity to be proportional to the linear velocity, with the ratio between the two being the twist value exactly. So when the bullet has zero velocity, like at the start of firing the gun, it also has zero rotational velocity, and it gains rotational velocity over time as it gains linear velocity. So constant twist rifling does NOT actually force instant rotational acceleration at the beginning like you suggested. I'm guessing this is part of why progressive rifling doesn't seem to help much. In an idealized physics gun where the bullet has constant acceleration, a constant twist would also cause a constant rotational acceleration, which would minimize twisting forces on the bullet, and hence be the optimal rifling. The thing is, in reality the bullet actually accelerates most at the start of the barrel, when the gas pressure in the barrel is highest, and then the acceleration drops from there as the gas expands and the pressure drops. Given this, progressive rifling may actually help by making the rotational acceleration closer to constant.
Keep in mind I'm a physicist, not a gun expert like you are, so I may be overlooking something.
I would imagine that a progressive twist barrel would give you a little bit more velocity. With progressive rifling requiring less initial energy to get the bullet moving would have to reduce the overall energy loss giving it higher velocity.
There is some data from High Power shooters that gain twist does provide slightly more velocity. Bartlein offers a gain twist 20” .223 Wylde.
Very cool, thanks for teaching us.
Beautifully answered.
Very interesting.
I had not heard of this concept before.
The S&W .460 mag has a progressively rifled barrel, the progressively riffled barrel for the 20mm is what arms the warhead on the projectile. 20mm projectile is an air burst item don’t want 20 mm bullets hitting the ground.
I wonder how the barrel wear varied as well with progressive twist.
Probably not much.
Barrel wear is usually concentrated to throat erosion & that has more to do with powder charge vs bore diameter.
This shift in the Q and A format is a win. I enjoyed the old format but it could be a little long for my tastes and this offers much easier indexing.
My Springfield 1863 Amoskeag got progressive depth rifling ! And I didn't knew it for quite a long time, made recalibrating my minié bullets a pain until I knew !
Excellent video. First, the function of the rifling is to make the James Bond's "Gun Barrel sequence" a true classic. My doubt is if there is any progressive rifling but that it starts out shallow and gets deeper as it approaches the muzzle of the barrel.
This format is great
I find today about the S&W .460, super interesting stuff.
Another reason is pressure. Progressive twist further deforms the rifling engraving as helix angle increases. Pressure maximum happens within inches of distance from the chamber. Initial slow twist reduces drag which reduces pressure. Increasing bullet drag later maintains pressure which assures efficient combustion.
Bore erosion is a function of pressure, not bullet friction. Pressure and temperature track together.
Early smokeless propellants were very hard on bore life due to this initial pressure spike.
The British added petroleum jelly to Cordite to reduce temperature, DuPont used deterrent coatings to extruded propellants, creating the Improved Military Rifle propellant line.
Now, on larger bore gain twist rounds, these typically utilize driving bands as the projectile is usually thicker steel which doesn't easily engrave rifling. Driving bands take gain twist better without jacket stress. And again, gain twist is used for pressure reduction.
Thanks for the lesson teach! Appreciate it a lot.
Greets, T.
Very informative, capandball has a great video explaining gain twist too.
I'd add that with progressive twists, the initial acceleration of the bullet is higher than with a uniform twist rate, because there is less initial resistance - however, the side benefit of that is a lessened peak pressure that has a somewhat gentler initial acceleration curve. Rifled shotgun chokes exhibit this behavior, where there is a noticeable difference in recoil between a smoothbore and a rifled-choke bore. There is also somewhat of a difference in recoil between a fully-rifled bore and the other two types. I've never been a fan of the the rifled-choke, as I've seen some weird slug patterns in comparison to the other two types. I visualize a round accelerating down the barrel, then suddenly having to encounter resistance in the form of the rifling's forced rotation. To me, this would result in the expanding gasses experiencing a millisecond of pressure spike; but a pressure spike that shouldn't be as high as the initial pressure spike upon ignition. My two cents of babble today.
Good to get in this great video early!
LMT has been working on this for a good while now for the 556.
It's almost weird how I was just thinking about this and here Ian comes with a bonafide answer per usual.
Very cool. Thanks for the video
Awesome as always! I thought of barrel wear and fouling ... But jackets separating from the core never occured to me. I wonder what the really big guns, rifled tank and naval guns, do. The look constant twist in the photos.
I’m correcting Ian mistake. He said 0-3000 rpm. A 223 with a 10 twist at 2800 fps is 201,000 RPM
If a 7 twist it’s 288,000 RPM.
Yeah, was going take my own comment. I couldn't find the twist rate of the Phalanx CWIS (M61A1), but assuming 1:12, at 3600 fps, it's 3600 revolutions per second, or 216,000 rpm.
I absolutely love your content Ian! You’re absolutely a genius.
Progressive depth is an Idea I have been looking into to get more speed out of Palma rifles as they require longer barrels than needed for smokeless. They require longer barrels for the sights.
The relatively new 8.6 Blackout from Q is engineered for a 1:3in twist. The high rate gives it more energy on target, especially for a long range subsonic cartridge. If they used progressive rifling they might get even higher twist rates without jacket separation. Unless of coarse they already do but I dont have the technical data :(
Thank you Ian, happened to be curious about this myself^^
from the title I was assuming it was just to give normal rifles even more spin than they would normally. now I know it had to do with the inertial forces of much larger cartriges. thanks to you.
IMO they probably use progressive twist in Gatling guns to reduce barrel heating. In a normal barrel all of the energy and thus heat from spinning up the projectile is concentrated at the breach where the bullet first engages the riffling. This is already where most of the barrel heating is going to be concentrated due to combustion and cutting rifling into the projectile. On a normal gun the extra heat from spinning up the projectile is too insignificant to worry about, but on a gun that fires 4,000 rounds a minute the heating is going to be much more substantial. By spinning up the projectile over the whole length of the barrel it spreads the heat out over the whole barrel.
....In addition spreading the friction of spinning up the projectile over the whole barrel should reduce barrel wear. Which is also important with a Gatling gun's crazy high rate of fire.
My instant thought was barrel wear reduction. Didn’t anticipate the decoupling of the jacket.
Bartlein makes gain twist barrels. Frank Gallie really likes them