bbl.Twists ?

Old Corps 8541 said:

from what I've read when the USMC's ** MTU started building the M-40's they used Bbl's with a 1 - 11.25 twist. I've often wondered why that twist ^^, and why only a very few barrel makers offer that twist today .
** Don't know about the Army's MTU
^^ running both the JBM and Sierra stability programs they both say a 1-12 will handle a 175 SMK ?

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It was the army M24 that had the 11.25 twist. First barrels were by obermeyer/rock(i think), then later Remington factory made them.

USMC M40 used 12 twist Schneider barrel.

Here's my understanding:

USMC:
1966 to 1977: M40's used 1/10 twist, 24" long barrels made by Remington. It was designed/assumed for use with the M118 ammo (174 grain bullet)
1977-2016: M40A1/A3/A5 used 1/12 twist, 24" SS barrels made by various makers, with Schnieder being the most common since early 200Xs. It was designed for the M118 and then in the mid-to-late 1990s the improved M118 LR round, which used the more consistent 175 grain SMK bullet.
2016-present day(?): M40A6 used a 1/10 twist, 20" SS barrel made by Schnieder. (Barrel shortened to 20" for shorter overall length w/ suppressor, and twist rate was increased to 1/10 to presumably provide enough rotational spin for the 175 grain SMK bullet in the shorter 20" barrel.)

US Army:
1988-2011: M24s adopted the 1/11.25 twist, 24" long barrels. Why? It's a good compromise. US Army snipers were trained to use M118 with 174 grain LC ammo (and later the M118 LR w/ 175 SMK), but in an urgent/combat situation in some foreign land, snipers needed to be able to shoot M80 machine gun ammo (147 grain bullet) out of an M24, and retain relatively good stability/accuracy. Obviously accuracy would suffer with generic M80 compared to M118 match ammo, but the 11.25 twist rate back in the 1980s was reportedly tested and adopted as the ideal compromise between the two ammo types that a US Army sniper would have access to in the field... Big Army being Big Army, presumably wanted maximum flexibility re M24 ammo usage. My 2cts.

As an anecdotal observation on the 10th Special Forces Group M14 sniper rifles made at Ft Devens MA (aka the M25 rifles). The original XM25 sniper rifles made in the late 1980s used a 1/10 twist 22" medium weight match barrel, but pics/documentation on the later M25s made circa 1993-94, showed that 1/11 twist heavy profile 22" barrels were used. The ammo used was the same in that era, M118 Special Ball. I thought that slight switch in twist rates was curious, but I guess by the early-to-mid 1990s, the 1/11 twist rate became popular, in part due to the M24's use of the unique 1/11.25 twist rate.

Random Guy I think is very close on what he all wrote.

Original M40 barrels where 10 twist and 6 groove for rifling. Just back in 2012 I got to look at and confirm that with an original M40 rifle barrel that was built back in 1966 that was here in the shop so we could check the exact contour dimensions etc...

As far as current M40 type barrels..I literally just quoted (like 5 minutes ago) some more 30cal for the PWS shop and again they asked for 10 twist barrels. I do believe these are team/match barrels. M40 contour and 5R rifling.

I have the whole M40A3 drawing packet and I can look to see what the barrel spec was called out if need be.

As Lowlight mentioned and I'll add a little more... a 12 twist will handle up to conventional 190gr match bullets at 308w velocities. Your pushing that though. I'd run a 10 myself. I've shot 8 twist, 10 twist, 11, 11.25 and 12 twist. I don't see a difference accuracy wise. 10 and 11 twist are my favorites.

Later, Frank
Bartlein Barrels

Ah, thanks guys....I have a Rem 700 5R SS Gen 2 (got to love dem' loooong names, right?) with a 20" 1/11.25 barrel and I often wondered with the 11.25 came from....particularly the .25 part! haha

Its just a bog standard eastern whitetail deer gun but it shoots 168/175 FGGM and 178 ELD-X just fine. I've not had any stability issues shooting it out to 300 yards which is as far as I'll ever need to shoot at a deer in my neck of the woods.

Cheers

Baron23 said:

Ah, thanks guys....I have a Rem 700 5R SS Gen 2 (got to love dem' loooong names, right?) with a 20" 1/11.5 barrel and I often wondered with the 11.25 came from....particularly the .25 part! haha

Cheers

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If I recall correctly but I cannot remember exactly who.... but either the military or a place like KAC or someone else wanted Obermeyer to make 11 twist rifled barrels but Boots didn't have the gear set up for 11 twist. So he picked the gear combination closes to 11. I think he ended up making 11.27 twist barrels but everyone called them 11.25 twist.

I might be partly wrong about that....but it's pretty close that's how the 11.25 came to be.

So places like Obermeyer, Krieger that do cut rifling and use Pratt hydraulic rifling machines....those machines originally where set up for one twist and in 30cal it would've been 10 twist. So Krieger etc...modified the machines with a gear plate/changing system. By changing a combination of gears they could do different twist rates.

We do single point cut rifling but we built new machines and do it all with cnc controls. So we can offer pretty much any twist you want. Tooling still plays a part to some extent.

Later, Frank
Bartlein Barrels

My understanding was also that the 1:11.25 was a gearing thing.

I researched this a couple of years ago when someone on a Canadian firearm forum claimed that 1:11.25 twist was the most accurate twist rate for .308 because that's what the military uses, and through their extensive testing on twist rates this is what they determined (of course with no sources). This guy was trying to tell me that 1:11.25 twist is superior to 1:10 on .308's because of this

So to prove he was full of shit I did my own research, and found out that it's like @Frank Green states - it was essentially a coincidental twist rate through gears on the manufacturing equipment. I don't remember the specific details however.

I have shoot well over 5000 rounds in 1-12 in a Steyr SSG04 and it shot 175SMK and 175 Berger great. till the barrel was worn out. I have about 2000 or so rounds on a Schneider 1-10 P5 26in barrel for my AI-AE and it shoots 178 ELD-M great. I shot a local 1000 yard match and scored 93 1x with 1 flyer in the 8 ring and beat guys shooting 6cm,.243,6.5cm, 6.5PRC, 7mm. The winner that day shot 96 3x.

lowlight said:

Wasn't the 11.25 Mike Rock ?

I thought it was Rock who coined the 11.25

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It might have been but I cannot say for sure.

Then I will say that goes back to Mike did work for Boots so I think it started back at Obermeyers shop. Best I can tell ya. You might be right that Mike coined it and pushed it to some extent at some point in time.

Wasn't the 11.25 Mike Rock ?

I thought it was Rock who coined the 11.25

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Then I will say that goes back to Mike did work for Boots so I think it started back at Obermeyers shop. Best I can tell ya. You might be right that Mike coined it and pushed it to some extent at some point in time.

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Attached is the history of the development of the M24's barrel circa April 1986 when the US Army's 'Market Research' statement was released, to the the July 1988 era, when Remington formally won the award. The twist rate was determined by formal testing back in 1986 of different barrels and twist rates, and Remington couldn't meet the Army's accuracy spec at first - but they settled on 1/11.25 w/ 5R rifling - which finally met the Army's accuracy requirements as outlined in the Market Research/RFI statement. It is also true that Boots developed the 5R rifling, and Mike Rock made the barrels for the 6 Initial Test Rifles and the 19 "First Article Test Rifles" circa 1987. I think Remington made all of the 'production' M24 barrels after the contract was awarded in July 1988. The Army received the first production 100 M24s on October 25, 1988.

Anyhow, hopefully the attached documents will explain some of that early history and the first 25 US Army trial M24s. Source of attached pics & info: Collecting the American Sniper Rifle 1945 to 2000, (2014), by Joe Poyer. (There are various errors in this book, but the section on the M24 history is from the Remington archives and interviews, and do not appear to have any errors that I can detect). Random last pic is likely from the 1988-89 era.

just busting out the necronomicon to resurrect this dead thread but you guys are the Bon Vivants of this sort of thing, so who better to ask?

This is what I heard regards the 11.25 twist so I'm interested to see if there's any credence to it.

What I got told was that the 11.25" barrel was actually specified by Army as it would keep the in service ammunition (can't remember if it was OG M118 or 118LR) stabilised across a multitude of environments, temps and elevations better than 1/12, without putting excessive stress on the bullet during the engraving process like a 1/10 (or faster) would.

Materials and manufacturing have changed since then so these things are no longer a concern but at the time it was worth mitigating.

Do you think there's any merit to this?

Cheers

Carso

173-174 grain M118 was the Army's specified de facto National Match standard until it was supplanted-replaced by 168-grain M852 (I believe in 1982).

M118 Long Range (with the 175-grain Match King) wasn't adopted until 1996.

Having shot 175s out of a 1-12 twist National Match M14 or M21 with its 22-inch barrel the twist was not fast enough to keep the bullet stable at 1,000 yards at Quantico and Camp Perry. I don't think 1-10 was ever used in issued (as opposed to competition) M14s and M21s.

1-10 was pretty much required to keep the old-style boat-tail 180-grain Match Kings stable out of an M14. The limiting factor for the M14 in Long Range Service Rifle competition was in generating enough velocity from a 22-inch barrel while also balancing twist rate -- you can keep a slow bullet more stable with a faster twist but you run the risk of bigger groups as the bullet goes trans-sonic.

I have no idea why the Army adopted 1-11.25. The Marines didn't have as big a velocity concern as their M40s and M40A1s had 24-inch barrels.

Stuff gets even more complicated considering the SR-25 / MK11 / M110 have 20-inch (and shorter) barrels.

sinister said:

173-174 grain M118 was the Army's specified de facto National Match standard until it was supplanted-replaced by 168-grain M852 (I believe in 1982).

M118 Long Range (with the 175-grain Match King) wasn't adopted until 1996.

Having shot 175s out of a 1-12 twist National Match M14 or M21 with its 22-inch barrel the twist was not fast enough to keep the bullet stable enough at 1,000 yards at Quantico and Camp Perry. I don't think 1-10 was ever used in issued (as opposed to competition) M14s and M21s.

1-10 was pretty much required to keep the old-style boat-tail 180-grain Match Kings stable out of an M14. The limiting factor for the M14 in Long Range Service Rifle competition was in generating enough velocity from a 22-inch barrel while also balanced twist rate -- you can keep a slow bullet more stable with a faster twist but you run the risk of bigger groups as the bullet goes trans-sonic.

I have no idea why the Army adopted 1-11.25. The Marines didn't have as big a velocity concern as their M40s and M40A1s had 24-inch barrels.

Stuff gets even more complicated considering the SR-25 / MK11 / M110 have 20-inch (and shorter) barrels.

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That's still interesting information mate. Thanks

I built an SR-25 for my son for National Match long range service rifle competition.

The typical Palma Match format at Camp Perry is unlimited sighters but a fixed time of 20 minutes (I think) for 15 shots for score at 800 yards; 2 sighters and 15 shots at 900; and 2 sighters and 15 at 1,000. If you are shooting in the Service Rifle class with an M1, M14, AR-10/SR-25 your gas system must function as designed (no gas cutoff). Rounds are typically loaded long for self-loaders as it's a slow-fire, single-load each round into the chamber per shot.

AR-10/SR-25 service rifles are specified with 20-inch barrels. Decent 175, 178, and 185-grain bullets will generally do better with a 1-10 twist or slightly faster (my son's has a 1-9 twist for Berger 185 Juggernauts). Faster twists generally support longer (and heavier) bullets.





These youngsters from the US Army Marksmanship Unit set the Interservice Long Range Service Rifle Team Match record score at Quantico, Virginia in 2012 with 20-inch iron sight AR-10s:

What I got told was that the 11.25" barrel was actually specified by Army as it would keep the in service ammunition (can't remember if it was OG M118 or 118LR) stabilised across a multitude of environments, temps and elevations better than 1/12, without putting excessive stress on the bullet during the engraving process like a 1/10 (or faster) would.

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That is possible, but the Remington archives show that Remington tested “multiple twist rates” back in 1986-87 in order to achieve the Army’s technical specification regarding accuracy. The archives don’t specify the various twist rates that were tested, but the Army did not dictate the twist rate, only that the rifle had to meet a certain accuracy spec with M118 Special Ball ammo. (M118 SB came out in 1983, but prior to that year it was M118 Match, circa 1963-82).

Apparently 11.25 twist provided the best empirical results. I can’t help but wonder if Remington was also trying to split the difference in performance, as the U.S. Army going back to the XM21 era of Vietnam issued M118 as the “Standard A” ammo for sniping purposes, but the XM21 could also be used M80 ball ammo, tracer, and incendiary ammo as an alternative.

- M80 used a (+/-) 147 grain projectile and 1/12 twist is considered ideal.
- M118 used a (+/-) 173 grain projectile and 1/10 or maybe 1/11 twist is considered ideal.

So 11.25 was a good compromise on the M24, as an overseas deployed US Army sniper might be stuck with ‘junky’ M80 machine gun ammo in a combat theater, so the rifle needed to shoot it well enough. Using M80 would only be in an urgent situation where the sniper ran out of the “good stuff”, (ie M118 Special Ball ammo). Thats my reading of the M24 rifle development.

Anecdotally, one testing issue that Remington encountered back in 1986-87 was that they needed a bunch of issued M118 Special Ball ammo to conduct their empirical testing. So they requested it, and the Army subsequently provided them w/ enough M118 SB to complete development of their prototype M24 test rifles.


FWIW, when I made my M24ish replica on the bottom (but with a short action), I used a Kreiger 1/11.25 twist 5R SS barrel to mimic the barrel pattern used on my factory M24R (at top.)

Digressing slightly, but I’ll note some historical info regarding this statement.

I don't think 1-10 was ever used in issued (as opposed to competition) M14s and M21s

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Yes and no. The exception were the quasi-exotic SOCOM/Crane-built M14 sniper rifles circa 1990-2012, plus some other “boutique” M14 rifles used by a few Army units. They used 1/10 twist barrels exclusively, but you are correct about Big Army’s combat M21s using only 1/12 twist barrels.

Here’s the specs for the Mk 14 Mod 2, which used a 1/10 twist commercial match barrel, same as the SSR and the PSSR of Desert Storm era.

Note: Crane had funding to make only 250 of these rifles (2011), and only 250 of the SSR (1996) and PSSR (1990) rifles, so they were all low-volume boutique rifles. The 10th SFG at Ft Devens, MA also used 1/10 twist Barnett barrels on the mysterious XM25/M25 sniper rifles circa late 1980s to mid-90s, but they were also low volume “boutique” rifles that lacked NSNs. Lastly, the Smith Enterprise-made “Crazy Horse” M12A5s also used a 1/10 twist barrel, but only 200 or so were made in the 200Xs, so they were also a boutique DMR rifle. (Note last sentence in first paragraph). Just some fyi research.