AR Pistol Barrel Length

[TNMTBik3r]

I have tried to research this and not finding a whole lot of info... hoping Dolomite or someone else with a wealth of knowledge can help enlighten me :)

 

Working on my first AR pistol, the lower is complete and I have been debating what I want to do for the upper. I have handled both a 7.5" and 10.5" 5.56 pistol and liked the balance of both. However, the 7.5" is considerably louder and the short barrel means less accuracy/velocity. The 10.5" is just a tad longer than what I would like to have.

 

I feel that a 9" barrel would be ideal - a good compromise in length, noise, accuracy and velocity. This length should allow for either a carbine or pistol length gas tube however I am not sure if a 9" barrel with a carbine length gas tube would be reliable - this is what I am looking for thoughts on.

 

I know that BCM went with a 11.5" SBR over 10.5" because the extra inch of barrel length resulted in 40% more dwell time and therefore increased reliability. How would a 9" barrel stack up? WOuld a carbine or pistol length be better?

 

I will be using an adjustable gas tube and reload so can somewhat tailor the loads to work properly.

 

I have found a couple of 9" or 9.5" 5.56 barrels online. They are not cheap though! I was thinking about buying a 16" carbine from PSA or similar and having a local smith cut it down and re-thread it (depending on their fee, would be a cheaper route).

 

And yes, this will be 5.56 - not going the .300BO route.

[Oh Shoot]

....  I have found a couple of 9" or 9.5" 5.56 barrels online. They are not cheap though! I was thinking about buying a 16" carbine from PSA or similar and having a local smith cut it down and re-thread it (depending on their fee, would be a cheaper route)....

 

No expert here, but quick thoughts:

 

- You'll need to consider barrel profile so that where it's cut can be threaded. Would then probably require free float rail, which is no bigger.

 

- You'll need to get a mid length gas system I guess to cut down, otherwise a carbine length gas port is gonna fall right about the very end of your cut off barrel, couldn't use it, but would still be there, heck might cut right in middle of it (don't know precise measurement).  Maybe weld up, but might interfere with threading?

 

- Anyway, one way or the other,  you'll need a pistol length gas port of correct size drilled too.

 

- OS

Edited October 22, 2014 by Oh Shoot

[TNMTBik3r]

I had planned on a free float rail regardless. 

 

I thought carbine length fell about 7.5" down?

 

Thanks, this is the kind of info I need. I plan on stopping in and talking to the 'smith this week to get the shops thoughts about it as well.

[Oh Shoot]

I had planned on a free float rail regardless. 

 

I thought carbine length fell about 7.5" down?

 

Ya know, it does seem to be about that by actual spec. I was quickly (mis)judging looking a the front of an A2 sight block, and even counting the barrel extension in there, duh. No expert indeed. :)

 

If barrel profile above it is suitable for threading, I guess carbine gas could maybe work okay on cut down 9-9.5.

 

Port would likely still have to opened up some though for the shorter bullet dwell time, as an adjustable block can't increase the max it gets to begin with.

 

edit: what do those 9"ish barrels you found use?

 

- OS

Edited October 22, 2014 by Oh Shoot

[jcluff]

http://angry-peasants.blogspot.com/2012/08/effective-range-of-your-223-or-556-rifle.html <- good resource for your barrel lengths and bullet effectiveness.

My pistol has a 10.5" barrel. The effective range is down to about 20 yards. That is sufficient. That effective range can be extended using defensive rounds.

The author of the article above is not a fan of 7"


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[Oh Shoot]

My pistol has a 10.5" barrel. The effective range is down to about 20 yards....

 

?? My 10.5 ARs get 2700 fts or more at muzzle from full power ammo and can pepper a torso fine at 100 yards with iron sights or red dot, so I consider that as a pretty effective range?

 

- OS

[jcluff]

?? My 10.5 ARs get 2700 fts or more at muzzle from full power ammo and can pepper a torso fine at 100 yards with iron sights or red dot, so I consider that as a pretty effective range?

- OS

I can hit stuff out past 200 yards with little difficulty, but the velocity past about 20 yards is below optimum for the 55gr fmj bullet to fragment. That is mostly what I load and shoot.

Winchester PDX and Barnes TSX, for example, will be effective a lower velocities.


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[TNMTBik3r]

Ya know, it does seem to be about that by actual spec. I was quickly (mis)judging looking a the front of an A2 sight block, and even counting the barrel extension in there, duh. No expert indeed. :)

If barrel profile above it is suitable for threading, I guess carbine gas could maybe work okay on cut down 9-9.5.

Port would likely still have to opened up some though for the shorter bullet dwell time, as an adjustable block can't increase the max it gets to begin with.

edit: what do those 9"ish barrels you found use?

- OS

I swore I found one that was carbine length but obviously not, or I didn't save it. The 3 I have saved are pistol length.

So I guess part of this discussion should be is it worth trying to make a carbine length work, or stick with a pistol length system?

[TNMTBik3r]

Great info Dolomite, thanks!
I will search for him on the net tonight and see what I can find. That price is about inline with the one barrel I found, and certainly cheaper than the Noveske.

[TNMTBik3r]

Gunsmith is moving to a new building and I haven't been able to catch them so far this week.

 

Ya know, going with a 10.5" barrel would be so much easier...it just isn't what I think I want  :)

[rugerla1]

Gunsmith is moving to a new building and I haven't been able to catch them so far this week.

 

Ya know, going with a 10.5" barrel would be so much easier...it just isn't what I think I want   :)

I haven't done a pistol yet but I think I'm going with the 10.5" since the extra length of the barrel isn't that much of a concern to me and they seem to be everywhere. Would I like a shorter one? Sure. I'll be watching your build to see how you like it. Good luck and enjoy the build, can't wait to see it.

[Dolomite_supafly]

I will say that a short barrel changes the feel of an AR.

[cgpeanut]

We'll decided to take the plunged and build a 7.5" pistol AR this would be my 3rd AR but 1st pistol AR. Already got all the parts except for the SIG SBX brace hoping to catch a good sale on Black Friday went with the voodoo tactical 7.5" in 556 and a Samson 9" evo rail, KAK muzzle device and Anderson upper/lower combo hope it works :)

[TrickyNicky]

We'll decided to take the plunged and build a 7.5" pistol AR this would be my 3rd AR but 1st pistol AR. Already got all the parts except for the SIG SBX brace hoping to catch a good sale on Black Friday went with the voodoo tactical 7.5" in 556 and a Samson 9" evo rail, KAK muzzle device and Anderson upper/lower combo hope it works :)

Sounds like my pistol but with a finer pedigree on some things. I imagine it will be great. The 7.5" barrel and KAK can make the perfect length with a 9" handguard. :up: