Midlength Gas Systems (split from the Colt Midlength thread)

[Default.mp3]

If anyone can find a downloadable version of the actual CRANE presentation document, that would be awesome. I did a quick google and didn't find it, although given the subject matter, that doesn't mean it's not readily available.

I am a fan of original sources.

https://partner-mco-archive.s3.amazo...1527866983.pdf

[Wondering Beard]

Source: http://soldiersystems.net/2018/05/14...d-performance/

Suck it, haters.

Question: I see that the test used M855A1 as ammo and a 14.5" barrel with a midlength gas system. Doesn't the use of essentially a +P round along with what I understand is an under gassed midlength system (16" is right but 14.5" makes it a bit under gassed for mid lengths, I was told, but I'm no expert) make the results less comparable than using a regular 5.56 pressure round and comparing a 14.5" carbine vs a 16" midlength? or would it make no difference?

[MistWolf]

Question: I see that the test used M855A1 as ammo and a 14.5" barrel with a midlength gas system. Doesn't the use of essentially a +P round along with what I understand is an under gassed midlength system (16" is right but 14.5" makes it a bit under gassed for mid lengths, I was told, but I'm no expert) make the results less comparable than using a regular 5.56 pressure round and comparing a 14.5" carbine vs a 16" midlength? or would it make no difference?

What primarily controls gas is the gas port diameter. The length from gas port to muzzle (Carbine, Middy, Rifle, etc.) determines how long there will be usable pressure at the gas port (which has nothing to do with how long the bullet is in the bore).

While the carbine length system takes longer to blow down, the middy taps into the barrel where gas pressure is lower. The higher the pressure, the tighter the tolerance of the port diameter must be to achieve the correct gas flow. It's about achieving a balance between blow down time and pressure at the gas port to provide good gas flow to the BCG.

[Unobtanium]

Question: I see that the test used M855A1 as ammo and a 14.5" barrel with a midlength gas system. Doesn't the use of essentially a +P round along with what I understand is an under gassed midlength system (16" is right but 14.5" makes it a bit under gassed for mid lengths, I was told, but I'm no expert) make the results less comparable than using a regular 5.56 pressure round and comparing a 14.5" carbine vs a 16" midlength? or would it make no difference?

M855a1 is not "+P". Its the same pressure as m855 currently as best as I can tell.

[jeep45238]

Isn’t a1 just a new bullet design?


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[Unobtanium]

Isn’t a1 just a new bullet design?


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Yes, but there are other new components as well, and the early lots used a very high pressure loading. They have been backing off on it for years, and it's currently hanging out around M855 spec, or a touch cooler.