AR Pistols: barrel length vs. gas tube length?

[Tactically Fat]

I think I may have it in my mind to build a 5.56/.223 AR pistol.

In my mind, I want a 11.5" barrel with a mid-length gas system + and adjustable gas block. Again in my mind, a gas block would be a tad easier to fiddle with than springs and buffers.

However, I think that having a mid-length gas system on an 11.5" barrel is pretty rare. And probably unnecessarily expensive.

So, perhaps a 12.5" mid-length + adjustable gas block?

I do plan on suppressing this in the future. And the suppressor would probably mostly reside on this (though it'd also be used on other hosts).

Again, I keep mentioning an adjustable gas block for ease of "tuning" between suppressed and unsuppressed.

Thoughts?

 

[Merk]

I run a 10.5 BA Hanson profile, carbine gas with and h2 buffer and it functions perfectly. None adjustable gas block.

Another option..

 

[Hohn]

Mid length was developed for 16" barrels. I don't think it's what you want for a 11.5 or 12.5" barrel. Carbine gas is the way to do for those short barrels. WHY?

Gas operation is about more than just pressure. It's pressure times TIME. The less time the gas is applied, the less tolerant of deviations in pressure. A super long gas system on a short barrel results in a very short period of "plug" time in which the bullet is sealing the barrel and still far enough down the tube to be forcing gas into the gas system.

If you have the AGB, then that's a reason to use the shorter gas system as you can basically adjust the flow per unit time for the gas system. And having more time (i.e. "cork time" in the shorter gas system) give you more effective adjustment.

A super long gas system on a short barrel great exaggerates the difference from round to round, and you'll end up with less functional margin overall.

I would never do midlength for 12.5" or less. I would only do it for 16" or 18 at the longest"

18 and longer IMO get rifle or longer.

 

[Tactically Fat]

Thanks for the responses!

My ultimate goal in wanting a mid-length gas system in a shorter barrel is merely for recoil feel issues. To lessen the harshness of the recoil.

And yes, I'm beginning to understand timing.

So perhaps I DO want a carbine system + AGB...

so. complicated. Especially since I plan to eventually have and generally keep it suppressed.

 

[OneBadV8]

Suppressors help with recoil

"harshness of recoil" ?

 

[Tactically Fat]

Yes - an AR, even a super short 7" barreled 5.56 version doesn't have exceptionally harsh recoil compared to many many things.

But a 11.5" AR with a pistol or carbine gas system will feel more harsh under recoil than the same gun with a mid-length gas system - all else being equal.

Poking with sticks, indeed! :-D

 

[Hohn]

Thanks for the responses!

My ultimate goal in wanting a mid-length gas system in a shorter barrel is merely for recoil feel issues. To lessen the harshness of the recoil.

And yes, I'm beginning to understand timing.

So perhaps I DO want a carbine system + AGB...

so. complicated. Especially since I plan to eventually have and generally keep it suppressed.

IMO, anyone planning on shooting both suppressed and not should strongly consider an AGB. Or live with the gas system far from optical for that huge increase in backpressure.

 

[romack991]

Check out the Faxon 11.5" Gunner. It's mid length gas and pretty inexpensive. I've been happy with mine.

 

[Tactically Fat]

Check out the Faxon 11.5" Gunner. It's mid length gas and pretty inexpensive. I've been happy with mine.

I've come across several threads about that barrel in my Googling.

Right now - I'm still wholly undecided!

 

[romack991]

There's not much dwell time. I've had a few issues with light competition loads when it's close to freezing. It has ran fine when it's above 40 or with regular ammo. It's fun as long as you realize it may have limitations.

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