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Armalite AR10 A4F build.......

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10 years 7 months ago #36843 by LebbenB
Replied by LebbenB on topic Armalite AR10 A4F build.......
Any issues with powder run out with the 14.5?

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10 years 7 months ago #36844 by faawrenchbndr
Replied by faawrenchbndr on topic Armalite AR10 A4F build.......
Not familiar with that term,..........?
As in excessive muzzle flash?

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10 years 7 months ago #36847 by OleCowboy
Replied by OleCowboy on topic Armalite AR10 A4F build.......
White man have STRONG medicine... :twothumbs:

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10 years 7 months ago - 10 years 7 months ago #36850 by LebbenB
Replied by LebbenB on topic Armalite AR10 A4F build.......

faawrenchbndr wrote: Not familiar with that term,..........?
As in excessive muzzle flash?

That's part of it. If the barrel is too short, the powder charge will not ignite completely while the projectile is still in the bore. This results in a larger muzzle blast and lower muzzle velocity of the projectile. It's also referred to as powder burn out. IIRC, the burnout rate for .308 is 15-16 inches, depending on the powder. I'm at work so I don't have access to my hard copy references.

If you have a chrony, I'd be interested in seeing what sort of MVs you're getting from it.
Last edit: 10 years 7 months ago by LebbenB.

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10 years 7 months ago - 10 years 7 months ago #36852 by faawrenchbndr
Replied by faawrenchbndr on topic Armalite AR10 A4F build.......
Do not have a crono available to check this barrel. Last short barrel, using m 118lr was clocking right at 2460.

My actual plan is to shorten the rifle length gas system, 18" barrel to 16"
Amazing shooters!
Last edit: 10 years 7 months ago by faawrenchbndr.

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10 years 7 months ago #36862 by LebbenB
Replied by LebbenB on topic Armalite AR10 A4F build.......

faawrenchbndr wrote: Do not have a crono available to check this barrel. Last short barrel, using m 118lr was clocking right at 2460.

My actual plan is to shorten the rifle length gas system, 18" barrel to 16"
Amazing shooters!

Interesting move. The trend has been to lengthen the gas system on shorter barrels. What's the gas port size going to be?

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10 years 7 months ago #36877 by faawrenchbndr
Replied by faawrenchbndr on topic Armalite AR10 A4F build.......
I'm not sure what LMT is using for a port size. I have no plans to open it up.

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10 years 7 months ago #36913 by LebbenB
Replied by LebbenB on topic Armalite AR10 A4F build.......
If you shorten the gas system, you have to tighten up the gas port diameter. If you keep the port diameter the same size, you over-gas the gun substantially (Same volume of gas moving a shorter distance means it gets to the BCG faster and acts on it with more force.) which leads to premature wear and tear on the bolt as well as to issues like bolt bounce and rocketing.
The following user(s) said Thank You: jtallen83

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10 years 7 months ago #36917 by OleCowboy
Replied by OleCowboy on topic Armalite AR10 A4F build.......

LebbenB wrote: If you shorten the gas system, you have to tighten up the gas port diameter. If you keep the port diameter the same size, you over-gas the gun substantially (Same volume of gas moving a shorter distance means it gets to the BCG faster and acts on it with more force.) which leads to premature wear and tear on the bolt as well as to issues like bolt bounce and rocketing.

Just wonder if you know how that is computed or do they use a table?

I would think there would be some standardization on that??????


.308 x bbl length / time of high tide = length of gas tube if gas port is ____?

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10 years 7 months ago #36929 by faawrenchbndr
Replied by faawrenchbndr on topic Armalite AR10 A4F build.......

LebbenB wrote: If you shorten the gas system, you have to tighten up the gas port diameter. If you keep the port diameter the same size, you over-gas the gun substantially (Same volume of gas moving a shorter distance means it gets to the BCG faster and acts on it with more force.) which leads to premature wear and tear on the bolt as well as to issues like bolt bounce and rocketing.


Have no plans to mod the gas system at all. There are a lot of these rifle length gassed 16" barrels being used with standard size gas ports. None exhibit bolt bounce issues either

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