Accuracy of 1:14 twist

According to the Black Rifle, Colt did extensive testing in 1967 with the 1:14 twist versus the 1:12 twist. Basically, the summary is that the 1:12 twist had an average spread of 3.6" at 100 meters whereas the 1:14 had an average spread of 7.2". They used various ammo lots of selected m193 ammo. According to the study, Colt was pretty careful to make the barreling process as similar as possible excepting the twist rate.

Have any of you had any better accuracy out of an early barreled 1:14 twist?

That sounds about right for 1 in 12 twist with military ammo. No idea about the 1 in 14, but will be interesting to find out if anyone does have some personal data. Double the spread sounds like a lot, but could be depending on the conditions of the tests and comparison.

There was a thread quite a while ago where someone was in touch with a barrel maker who might be willing to do a run of 1 in 14 lightweights. Always wanted to have a shooter 1 in 14. See if I can find it later.

I've only fired through two of my 1-14 barrels, and have not attempted a controlled study by any means. But my general impression has been that the 1-14s weren't significantly less accurate than most of my 1-12s. Of course, some of my 1-12s do much better than others.

To replicate the study, unfortunately, we'd have to take about a thousand variables into consideration, starting with condition. Since these old barrels are, well...old, there's no guarantee that they'll shoot today like they would have when they were new.

Now, if we assume that, in general, these retro barrels suffered similar use and conditions over the year, we might conclude that the more accurate twist (today) was probably the more accurate (then). But that's an unrealistic assumption to make about any individual barrels. To hold any validity, that assumption requires sizable study samples––more than just a few barrels of each twist.
Then, once we have the samples, we'd also have to control as many other factors as possible––wind, temp, ammo, triggerman, etc. That means the tests should be conducted over a short period of time, in one location, with the uppers mounted on a single lower, fired by a single shooter.

In the interests of retro science , I would be willing to perform these tests. All I need is for everyone to send me your 1-14 barreled uppers (and maybe a few bucks to defray ammo costs?) and I promise to get them back to you (eventually)!

What's more, I'll return your uppers to you uncleaned ...so you'll have absolutely no doubt that your barrel was actually fired during these historically important tests.

Too dangerous - THEY'LL TEAR YOUR ARM OFF! Seriously though, there is something to this. The inherent instability of the original round through 1:14 was similiar to what the Russians later did with the 5.45x49 round. The Ogive of the newer rounds is different from what I understand - in other words, you would need to handload some original, or close to original bullets to get the same test results. I've always wondered about pulling some 5.45 bullets and replicating that round. Tumbling is what it's all about, and at 50yd engagement ranges, accuracy was likely hardly an issue. Compared to the M1 carbines then in use by advisors and CIDG forces the 5.56 probabaly came out looking pretty good. I'm just guessing, but I bet those advisors cleaned their weapons regularly and rarely fired them FA as well, except for breaking contact. This is actually very similiar to the current needs of civilian 'homeland defenders' so I think any retro AR ought to do quite well in a confrontation, even with M193, which is clearly not as devastaing as the original round, through the original twist. Dewatter's 5.56 guide has more info on this, and good stuff. Hard to wade through, but well worth it.

Not much differance with general accuracy at normal temps... IIRC, it wasnt until testing in extreme cold tempatures (-30ºF and colder) at the Army's CRTC that accuracy issues then started to surface.

Not much differance with general accuracy at normal temps... IIRC, it wasnt until testing in extreme cold tempatures (-30ºF and colder) at the Army's CRTC that accuracy issues then started to surface.

This as a general rule is what I've always been told. In 1967 a 1-14 was at least a few years old. Was also always told to stay away from the 1-14 barrels for serious shooters as far back as 25 yrs ago due to the wear factor and the main reason they were usually replaced. There are pristine exceptions but a well used 50 yr old service barrel isn't going to be known for it's accuracy in most cases. 'Milspec has always been 2-4 inch as far as I know 1-14, 1-12 or 1-7 with exception of MK-262 through a 1-7 and in most cases ammo was the weak link but there's the BCG, FCG, conditions etc. Most all USGI M-16's in good shape will easily achieve this spec but they get logged, serviced and replaced over time, then we buy them up cheap. I'm definately not gonna dispute anything in Black Rifle but I'm just repeating what people I would trust with my coins and health have told me.

Y'know, since the 1:14 barrels were produced by Winchester, and the 1:12 barrels ended up (at this time) being produced by Colt, I'd expect that.

Not that Colt would come up with a disparaging report about one of their competitors... Marketing being what it is.

It's like General Motors conducting comparison testing on the Chevy Volt vs. the Toyota Prius for a big commercial contract. Which one do you think will fare better in their report?

Remember, Colt made 1-14's, too. They only subbed them from Winchester until they got their own barrel equipment up and running.
Not sure what the division was in terms of numbers, but two of my three 1-14 barrels are Colt. Only #748 came with the Winchester.

Doesn't sound right, because 7 MOA was the reject point where you could turn an A1 in for depot maintenance. That would be a 7 inch group at 100 yards (from a rest, of course).

Colt did have a lot of production QA/QC problems in the sixties.

I just learned (from reading the declassified "History of the M16 Weapons System" volume of the "Report of the M16 Rifle Review Panel" dated 1 June 1968 –– that the Army wanted to stay with the 14 inch twist. The Air Force insisted on the change. Of course, their dudes were guarding nuc bombers and missiles in garden spots in North Dakota.

Okay, I'm looking for the page reference now. And not finding it....

Edited to add: You will not find success with 5.45 slugs in an AR barrel. They'll keyhole. (Edited again to expand on this). The difference between a nominal .224 and nominal .221 slug seems nugatory, but it isn't. It's a tenth of a millimeter but it makes all the difference in the degree to which the jacketed bullet, which does not expand much, engages the rifling. When the BATF banned importation of barrels, fly-by-night operators (Century, feel your ears burning?) substituted barrels that were made with 5.56 in mind, just re-chambered for the 5.45x 39. It didn't help that the barrels were bottom-of-the-barrel (pun intended) for quality, too, but ask around on an AK forum about those repurposed 5.56 barrels. There's a reason that your new AKM-74 from Century doesn't include a test target :/ [ end of edits]


There were actually two original bullets that were under test, the standard Remington one that became the M193 bullet and an alternative from Sierra. Teh Army bought the Remington bullets as part of furnished rounds, and the Air Force bought the Sierra bullets as components.



Source: Report of the M16 rifle Review Panel, Appendic 4: Ammunition Development Program. pp. 4-23, 4-24.

Technical enough for you? It gets even more complicated after that.



I strongly concur. Not only has Daniel Watters done that great page at The Gun Zone, he's also the guy who turned me on to the document containing the above info, in a comment on my blog. There's tons of info in the primary sources, the same documents that probably informed The Black Rifle. Although it's hard to tell, because TBR's sources are undocumented, no footnotes or anything. .

Thank you, Hognose. Actually, I don't think that the authors of TBR had the full 12 volume report when they wrote the book. I do know that they managed to get copies of the PMR's Weekly Significant Action Reports via a FOIA request. The WSAR are constantly cited throughout TBR. The Ichord Subcommittee transcripts and report play a big role, and I think William C. Davis, Jr. fed them a whole bunch of the reports which he had written during his career.

FWIW: The 1-14" and 1-12" twist barrels tested during 1967 and 1968 were all new production from Colt. The early results were noted in passing by Colt's Paul Benke during the 1967 Ichord Subcommittee hearings. There were supposed to be 1,000 barrels apiece for each rifling twist rate, but Colt employees goofed and accidentally mismarked a couple. This mismatch was caught, so there were something like 1,002 of one and 998 of the other.

Very interesting discussion gents, and thanks for your input. The 5.56 Timeline is an awesome reference for anyone interested in the development of the AR15, the cartridge, and related weapon systems...nicely arranged in historical sequence.

A lot of Benchrest and varmint shooters use the 1/14" rifling in both .30 and .224 bores, but I believe accuracy out of them is a balance of velocity, bullet bearing surface engagement, bullet design, and bullet weight as it pertains to barrel time.

A simple comparison between 1/12 and 1/14 twists is better understood with more focus on the other variables, since accurate loads can be developed for both.

Now I'm interested in which bullet manufacturer won the contract for the projectiles, or was it farmed out for the M193?

Hognose, can you please link your blog?

The original intent was for the rifle to fire a 55 grain projectile at 3,300 fps. However, they weren't able to reliably mass produce that loading without over pressure issues, so the standard was dropped to the now infamous 55 @ 3,250.

Thanks all who have replied to this thread.One of the BEST ones I've seen in a very long time.

Well, I still think you should all send me your 1-14" barrels to be tested!

I agree^^^^^^

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