Most Effective Caliber for a AR Pistol?

[Rorge Retson]

Finishing my first 80% lower here shortly and looking forward to my first AR pistol build. Pondering what to chamber it in.

I like the idea of a shorter (~7") rather than a longer (~10.5") barrel, which I know will factor into the decision.

I'd also like something I can hang onto for follow-on shots.

Here are my top three contenders as of now, but looking for alternatives and input (based on experience, not conjecture):

- .300AAC Blackout
- .458 SOCOM
- 6.8 SPC II

Am I missing anything from my short list?

 

[RAINS]

I'd say 7.62x39 but I don't know that anyone currently makes decent mags. With that short of a barrel you would still get great performance out of a pistol caliber. Say 10mm or 45 acp. Still if you want pure power go for that .458!

 

[crazy-mp]

I would go with a 9mm you can get complete uppers reasonably cheap, they are fun, the .458 will be a handful...literally. Plus if you ever want to make it a SBR, the 9 will be a great one to put a stock and suppressor on!

300 BLK would be a good option as well, suppressed it would be a great show and tell gun.

 

[tepin]

+1 on the .300

 

[dprice3844444]

cmmg makes an ar lower that accepts ak47 mags.

 

[justice06rr]

300BLK, but with a 8.5inch barrel instead. you'll also have the advantage of using all AR parts and save some $$ for amoo

 

[MasterSergeantA]

Not sure how you personally define "effective", but I have built pistols in:

.22LR
5.56
6.8 SPC
.300 AAC
7.62x39
9mm
.45 ACP
.50 Beowulf

The .22LR is cheapest to shoot.

The others are pretty loud except that I use a can on the 9mm most of the time. The Beowulf is a handful, but would be "effective" against an intruder.

All are 7.5" barrels except the 6.8 and 7.62x39 which are 10.5".

 

[Rorge Retson]

300BLK, but with a 8.5inch barrel instead. you'll also have the advantage of using all AR parts and save some $$ for amoo

How does one more inch change things that drastically? What can't I use with a 7.5" gun?

All are 7.5" barrels except the 6.8 and 7.62x39 which are 10.5".

How do you like the .300AAC in 7.5"? (All signs seem to be pointing in this direction for me at present...)

 

[wally]

cmmg makes an ar lower that accepts ak47 mags.

Unless this is really new, I think you mean RRA, but unfortunately it also requires their proprietary upper as well.

MGI makes their "Hydra" with interchangable mag wells, not sure how well it works, read mixed reviews, but its too pricey for me to want to try one.

 

[68wj]

A THR deal never hurts: http://www.thehighroad.org/showthread.php?t=679573

 

[Double Naught Spy]

- .300AAC Blackout
- .458 SOCOM
- 6.8 SPC II

Am I missing anything from my short list?

With any rifle calibers, you are going to have LOTS of unburned powder and larger muzzle flashes even with hiders. If you are going to suppress the pistol, that will change, of course, but then you have a much longer barrel.

You aren't likely to get quick followup shots with these compared to shooting something like 9mm which will do great out of a 7.5" barrel.

So the question is, most effective for what? What sort of effectiveness are we talking about?

 

[Zoogster]

The .50 Beowulf would probably be the most effecient. Being similar to a .500 S&W round you could probably load it perfectly for an AR pistol length barrel.
It should have a lot more surface area to fully burn the powder in the barrel, and the round being slower and working more on mass than velocity will lose less energy out of a short barrel than the smaller rounds.


It may not be the most realistic to shoot, but it would probably have the least amount of wasted powder.


300 AAC Blackout likewise should be efficient in a shorter barrel. For similar reasons.


High velocity rifle rounds designed to be fired in a rifle generally need a rifle length barrel to perform well.

 

[Rorge Retson]

A THR deal never hurts: http://www.thehighroad.org/showthread.php?t=679573

Is that a good deal? I am not familiar with dealing with unfinished barrels. What all would need to be done to that barrel?

 

[JShirley]

looking for alternatives and input (based on experience, not conjecture):

Not MY experience, but thousands of Germans fell to 7.62x25mm subguns. Ammunition is still also cheaper than other centerfire ammo.

John

 

[peyton]

I would reccommend the 300 blackout.

 

[justice06rr]

How does one more inch change things that drastically? What can't I use with a 7.5" gun?

From my own extensive research into 300BLK, the ideal effective length is about 8.5inches minimum, up to maybe 11-inches. IIRC a barrel of 8.5inches the 300Blackout has more power than a .357Mag.

Since you mentioned a pistol AR, anything over 10inches is too long for me personally. If you wanted a barrel that long you might as well go with an SBR setup, but that involves NFA and part of the pistol AR's appeal is no NFA involvment.

I'm also building a pistol AR and I'm torn between a 7.5inch in 5.56/223, or the more expensive 8.5inch 300BLK. My lower is already built, just waiting on the funds for the upper and barrel. I'm undecided because I have two 16-inch AR15's, one in 5.56 and the other in 300BLK; just a matter of deciding which route to go with. I like both, but the availability of 5.56/223 make it more attractive, but I also want a larger caliber.

 

[Mp7]

i really like the Tokarev idea!

 

[MachIVshooter]

10mm. The 10mm is the autoloader equivalent of .357 mag, with virtually identical internal and external ballistics. Out of a 7.5" barrel, it'll have more energy than 5.56 or .300 Blk, but still very manageable recoil; The .458 Socom or .50 Beowulf are gonna belt you in a 5 pound pistol.

Unfortunately, Olympic Arms is the only manufacturer I'm aware of currently offering a 10mm upper, and they're proud of them (~$750 last I checked).

I'm probably going to get one, and run it at 10" with no flash supressor. For now, my pistol (SBR as soon as the stamp comes back) is chambered in 5.56. Still fun! It's currently a 7.5" with a flaming pig (Noveske KX3) on the end.