5.56 Barrel length trade-offs... 10.5 vs 11.5 vs 12.5

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Virtual.Chris

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The reading I’ve done so far seems to indicate that 10.5“ (or 10.3”) barrels are not ideal and that the added dwell time from 11.5 provides much better ballistics. However, I understand the MK18 is a 10.3” setup and that obviously worked well for certain armed forces.

Besides muzzle velocity, are there any other considerations when selecting a barrel length in this range?

What’s the wisdom of the community here have to say?
 
Virtual.Chris said:
The reading I’ve done so far seems to indicate that 10.5“ (or 10.3”) barrels are not ideal and that the added dwell time from 11.5 provides much better ballistics. However, I understand the MK18 is a 10.3” setup and that obviously worked well for certain armed forces.

Besides muzzle velocity, are there any other considerations when selecting a barrel length in this range?

What’s the wisdom of the community here have to say?
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Nobody said it doesn’t work but it is much harder on parts. Go up to 11.5 or 12.5 imo. Significantly less wear and better ballistics.
 
cdndfs said:
Nobody said it doesn’t work but it is much harder on parts. Go up to 11.5 or 12.5 imo. Significantly less wear and better ballistics.
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I think you have to do different gas lengths to reduce wear. If you're increasing barrel length but the same gas system, you're going to have more gas coming back, same PSI pressure (same gas length), same amount of wear if not more.

In terms of ballistics, 11.5-12.5 ballistics are better for 55grainers since it takes fragmentation out to 100 yards or so, vs 10.3 being effective only at room distance (the way this length was chosen)

In terms of wear, rifle length gas would be the best, although midlength is already a big step up. Your gas port would also wear more with carbine length gas port since it's dealing with much higher pressures.
 
I should mention the rifle uses a carbine length gas system which wont be changing. So does barrel length affect anything other than the bullet?
 
Virtual.Chris said:
I should mention the rifle uses a carbine length gas system which wont be changing. So does barrel length affect anything other than the bullet?
Click to expand...

Increasing barrel length with the same gas port size(apples to apples) increases the amount of gas coming back(or longer dwell time). Longer dwell time(longer barrel length) apparently is better for reliability over larger gas port.
 
In AR and other American made rifles, I generally prefer 11.5 over 10" for a few reason. Muzzle velocity is a big one, the incremental velocity change between 11" and 10" is big relative to other barrel length. Putting aside terminal ballistic, external ballistic wise, when you are playing in the lower velocity threshold, every fps means more noticeable drop over 150m. Those couple inches more of drop start building up quickly beyond 200m. Not an issue in KD range, but it becomes more difficult in a non KD field range.

I also dislike 10" for another reason, many companies like to build handguards that are flush with 10" muzzles. I like the muzzle at least an inch beyond the handguard for a few reasons.
 
If it's an all around gun I would go 11.5. The recoil impulse on my MK18 is definitely different and sharper than my 16" ar. Even though both have Carbine length tubes. Added velocity is nice but if it's a strictly CQB setup the 10.3 is godly
 
I know jack about short barrel ballistics but they are Fun!
Here's a pic of my son trying to set the target on fire with a 10.5" LMT AR15....the Good Old Days.
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personally i prefer the 12.5" but in a pinch I'll build a 11.5".

the slight increase in the 12.5" muzzle velocity +~70FPS over the 11.5 or +~150FPS over 10.5 it enough to justify the 1-2 inch of barrel.
 
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