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Colt M4 cutaway (courtesy

The M16 is one of the most recognizable firearms in our recent history. In the 1950s, a new select-fire rifle was developed by an engineer named Eugene Stoner known as the AR-10, chambered in 7.62x51mm NATO. Shortly afterwards, Armalite introduced a modified design that was more compact and chambered for .223 Remington known as the AR-15.

The AR-15 became the basis for Colt’s M16. This military rifle, chambered for the 5.56x45mm intermediate rifle cartridge, saw its introduction during the Cold War, more specifically Vietnam. Between its introduction in the 1960s and the end of the Vietnam War, Colt produced millions of these firearms.

Colt M4 cutaway (courtesy

This M16 is different in appearance than the standard issue rifle. It’s a factory cut-away. Cut-aways have been developed for both marketing and training purposes. And they’re dream artifacts for curators because they provide insight to the visitor on the inner workings of these firearms. This particular firearm, made in 1967, was a gift from Colt to Mr. Fred Palmer in appreciation of his service as a military inspector at Colt during the Vietnam War.

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  1. I think we should still use the 1:12 twist barrel with the old m193 bullet. The wounds that would make was amazing. At least from what I’ve read. That was well before my war.

    • Hmm. I am going to infer that a 1:12 twist barrel was marginally stabilized for a 55 grain bullet and said bullet was thus much more prone to tumbling upon impact with human tissue. Is that about right?

      Standard barrels today seem to be at worst 1:9 twist and many are even 1:7 twist to stabilize heavier 77 grain match bullets. I never realized that faster twist rate “over stabilized” (if you will) bullets and reduced their likelihood of tumbling.

      • It doesn’t make it less likely to tumble when it hits an object, but it can make them unstable in the air. If you are using super-lightweight (<55gr) varmint bullets with a 20"; 1:7 barrel you might have problems with this "overstabilization," but it is mostly just a myth used to sell the cheaper 1:9 M4-profile barrels to gullible dupes who are never going to shoot anything but XM193 and XM855 anyway. Objectively, 1:7 is the best twist rate, and 20" is the best barrel length (although you could make a case for 24" barrels if you're just shooting from a bench all day). As you go shorter, your twist rate needs to stay higher or you will be unable to shoot heavier bullets. 1:7 can shoot 80gr, 90gr, and even 110gr bullets, and 1:8 will do just about anything up to the new-ish Barnes 85gr in any barrel length down to like 10", but once you get down to 16" with a 1:9 you lose the ability to shoot 64gr M856 tracers and boat-tailed bullets over 69gr (but you can still use flat-based bullets up to 75gr like the Hornady TAP). Never buy a 1:9 barrel less than 16", because it will be horrendous.

  2. The advantage of an SKS over the AR-15 is that it comes apart entirely, easily, and quickly … and thus you don’t need a cut-away view to understand it. I wish the AR-15 were as simple and came apart as easily.

    • I learned to field strip the M16 in less than 60 seconds. It is very easy to field strip and maintain. I did not need a cutaway version, I would hazard to guess that the Russians had similar tools in their armorer classes for the SKS and AK.

    • I’ve got several AR15s and consider them among the simplest guns I’ve ever had to field strip…they are almost ridiculously simple…anybody who needs a cut-away to figure out an AR15 should probably stick with an SKS.

  3. Sorry, guys, I can’t withhold some information I believe is pertinent here. When I graduated from pilot training in 1970, it was common knowledge that the M16 fired triangular bullets that tumbled right out of the barrel and caused bodies to explode. I had been PotG for 10 years by that time, this seemed suspect to me. Since I was enroute to a SEA combat job, I was sent to qualify with the M-16 in late 1970. My qualifying scores were all in the head of the silhouette, and still I qualified expert. Wow, I loved that gun! Obviously, I became aware instantly that the bullets were not triangular, wondered how much else was bullshit. In Vietnam, I came into possession of a magazine pouch with 3 AK mags in it. Another common story, which a hoochmate insisted was real, said that an AK could fire M16 ammo, but a M16 could not fire AK ammo. I told him that one was .30 and one was .223, making that concept ridiculous, and he said I was wrong, he knew all about it. I pulled an AK round out of a mag, and a 5.56 round out of my XM177-E2, and put them together on the desk in front of him, asking how he thought it could be possible that any rifle could fire both rounds. And he purely blew me off, he knew that they could because he had read about it. The intentional, deliberate stupidity cannot be overestimated.

  4. “The intentional, deliberate stupidity cannot be overestimated.”

    a psychologist would say that he was “invested” in his misinformation. having spoken out loud, he can’t back down because that would be an admission of error, which no Red Blooded All American man can do.

    a misguided notion of honor and pride. the root cause of countless bar fights. his problem isn’t your problem.

  5. We had a couple of cut aways at the Ordnance School. The real story is just how hard it is to make the cut away work without having the weapon collapse- there is a lot of work behind the scenes to make that model.

  6. Very cool.

    Ashley, any chance you could add a hi-res version of the top photo, please?

    (The higher the better)…

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