AR Pistol Cartridge Choices

[BigNate]

EDIT... Sorry for the novel... the question is "if, as a non-operator but serious shooter you were building an SBR / AR Pistol as a tool - what cartridge would you choose. Read on if you have time on your hands...

I'm building an AR pistol for a variety of reasons...
1) I want one...
2) I want to do some CQB type training and learn to better use this sort of weapon...
3) I want something with better energy and range and capacity than a standard handgun, but that can be used in close quarters, can be carried and maneuvered easily in the cab of a truck, and can bring more firepower to the fight than a handgun.
4) Once I feel competent with it I expect it will probably become the preferred nightstand gun...

I bought a generic lower a while ago - mostly so I'd have one - and I'm starting to think about cartridge options. I've "though about" the following:
5.56X45
.300 AAC
9mm
.40 SW
.45ACP
.458 SOCOM
.50 Beowolf
.450 Bushmaster

Right now I'm leaning .300 AAC - and here's why.

I eliminated the pure pistol calibers (9mm, .40SW, .45) because I want more energy and range than I would get out of these. Yes - they come out of a 9.5" barrel nominally hotter than they do from a 4" barrel - but not "enough" hotter. I want this gun to substantially outperform pistols in terms of terminal ballistics - and running a pistol caliber, well, won't.

I eliminated 5.56X45 (and candidly a few others like .224 valk etc.) because I want to be able to load subsonic for use suppressed. I don't know for sure that this is how it would get used - but I want the option and the small fast rifle cartridges either can't get there - or if they do they lack the energy that I'd want.

I have not eliminated the three big-bore cartridges but I'm leaning away from them for a couple of reasons. First - capacity - I understand that .50 Beowulf and .458 SOCOM will get me 10 rounds in a 30 round AR magazine and the Bushmaster will get me 13. When compared to the .300 AAC's 30 round capacity it is a hard pill to swallow. Second - cost to shoot and train - at $150+ per 100 rounds it is 3X the cost to shoot and practice as the .300 AAC. I have not eliminated them because... the energy... I love my .45-70 for a reason, and the idea of a semi-auto SBR/Pistol that shoots a large bullet at energies that are a healthy fraction of the .45-70 is really appealing. I'm just really having a hard time justifying the cost and loss of capacity.

This leaves the .300 AAC blackout. What are the flaws in my logic - and what other cartridges should I be considering?

 

[QuietM4]

If your goals include running it suppressed with sub sonic rounds, 300 Blackout is the only real choice. An argument could be made for 45acp as well, but getting an AR platform to reliably run 45acp can be difficult...more so than 300 Blackout. Granted, nothing with a suppressor on it is going to be "hearing safe" inside a hallway...might want to add some electronic hearing protection to your nightstand setup.

 

[XJThrottle]

I built a 300BO SBR when going through a similar thought process.

 

[kenpoprofessor]

If your goals include running it suppressed with sub sonic rounds, 300 Blackout is the only real choice. An argument could be made for 45acp as well, but getting an AR platform to reliably run 45acp can be difficult...more so than 300 Blackout. Granted, nothing with a suppressor on it is going to be "hearing safe" inside a hallway...might want to add some electronic hearing protection to your nightstand setup.

I've got 2 AR45s I assembled and not one has had problems, same with the 4 9mms I assembled. Everyone that says they have issues didn't do enough research to find out how to make them operate well the first time. RJ and Tony had a problem with theirs, after months of trial and error, I loaned them mine to use to swap parts. It was the magazines they were using, mine had an original Glock 21 mag in it when I loaned it to them.

Have a great, gun carryin', Kenpo day

Clyde

 

[Suck My Glock]

If your goals include running it suppressed with sub sonic rounds, 300 Blackout is the only real choice. An argument could be made for 45acp as well, but getting an AR platform to reliably run 45acp can be difficult...more so than 300 Blackout. Granted, nothing with a suppressor on it is going to be "hearing safe" inside a hallway...might want to add some electronic hearing protection to your nightstand setup.

Another option is the CMMG Banshee in 10mm. Using 200 grain projectiles, it can be subsonic. When using +P ammo like CorBon or DoubleTap, you can get incredible velocities and good performance 100 yards or further. Then there is the magazine compatibility with a G20 carry piece.

 

[YNOTAZ]

Any blowback round you use in an AR could have issues. Most issues have been worked out on the 9mm since Colt had the 9mm sub-gun on the AR platform, mags BCG, buffer weight and springs, piece of cake.

I started my 45 build before any were available and played for well over a year. Clyde was correct in one respect, actualy it was his bolt that made mine and RJ’s guns run. The mags were a different issue that added additional problems. We only solved the mag problems after we got the guns running reliably. There also seemed to be an issue with the particular lower and the Bolt. Mixing and matching gave different reliability.

In any case I have on CMMG rotating bolt AR45 and on straight blowback AR45 that both run, suppressed or not.

Other builds; I like the 300 blackout, (originally 300 whisper). I know the guy that designed it and I know what his objective was. It aint a long range deer cartridge. The ballistics with heavy bullets are about the same as a 45ACP. With a good can it is very quiet when loaded subsonic. I have one with a 10.5” barrel and I use an older model YHM suppressor, rated down to an 8” barrel and MGs, on it. That work great.

On to big bores, I also have a 458SOCOM that I’m still playing with loads on. I have it relatively quiet in a 10.5” and a Hybrid 46 can but I think I can do better with accuracy and different bullets. Advantage is it uses standard AR mags, some feed much better than other, Hexamag being one that feeds great, and it uses 45-70 bullets of which there are a lot of choices. I just haven't taken the time to play with this enough but I like what I see so far.

 

[iammaxwell]

[mention]BigNate[/mention] you looked into 350 legend? Your logic on 300 bo is solid BTW.

 

[XJThrottle]

@BigNate you looked into 350 legend? Your logic on 300 bo is solid BTW.

Problem with .35 caliber is the suppressor availability. You have to go up to the ones that will accept .35+caliber RIFLE stuff. You jump up to the big boy stuff then.

There are plenty of .45 caliber PISTOL suppressors out, but don't think you can substitute. You can't.

I have a SiCo Octane 45 (pistol can) that will take 300BO SUB loads only, and a Dead Air Ghost-M that does the same.

They will not take my 450Bushmaster..

When I was shopping RIFLE cans I went with the 762 Saker. I wanted something to maybe shoot with my 300WM, but mainly to use with anything smaller already in my safe..300WM inclusive.

....buying the Saker and getting the Octane for free was also a bonus...if you exclude the 2 year wait..

 

[Gatsby]

The 300 BLK was my choice because of flexibility. I run an 8-1/2" barrel, piston configuration for the can. I primarily shoot 220 grain subs at 1050fps, but I have mags loaded with 165 TSX barrier blind, 150 grain soft point at about 1850 FPS, and 190 grain Hornady Sub-X for defensive use (good luck trying to find them at the moment!). I'm not saying the other options can't be made flexible, but the BLK seemed to fit my needs well, and is always with me.

 

[BigNate]

If your goals include running it suppressed with sub sonic rounds, 300 Blackout is the only real choice. An argument could be made for 45acp as well, but getting an AR platform to reliably run 45acp can be difficult...more so than 300 Blackout. Granted, nothing with a suppressor on it is going to be "hearing safe" inside a hallway...might want to add some electronic hearing protection to your nightstand setup.

Thanks @QuietM4 – I’ve been looking at data on these cartridges and candidly one of the struggles that I’ve had with the 300 Blackout is the “pistol level” energies when shooting subsonic loads. However, when I look at it logically, the .300 is way ahead of the pistol calibers in that I can both shoot heavy / slow 220gr bullets when the situation calls for it – and can then swap magazines and effectively double energies and more than double effective range by going to lighter faster bullets. I think I’ve basically eliminated the pistol calibers. I have an old JR Carbine in 9mm that I really like – fantastic plinking gun – but probably not something that I’d carry to defend myself.

@BigNate you looked into 350 legend? Your logic on 300 bo is solid BTW.

I haven’t (or hadn’t) until you mentioned it. It is no on the list and a solid contender. The extra 120 – 150 ft/lb at muzzle when subsonic has some real appeal. Thanks!

@BigNate you looked into 350 legend? Your logic on 300 bo is solid BTW.

Problem with .35 caliber is the suppressor availability. You have to go up to the ones that will accept .35+caliber RIFLE stuff. You jump up to the big boy stuff then.

There are plenty of .45 caliber PISTOL suppressors out, but don't think you can substitute. You can't.

I have a SiCo Octane 45 (pistol can) that will take 300BO SUB loads only, and a Dead Air Ghost-M that does the same.

They will not take my 450Bushmaster..

When I was shopping RIFLE cans I went with the 762 Saker. I wanted something to maybe shoot with my 300WM, but mainly to use with anything smaller already in my safe..300WM inclusive.

....buying the Saker and getting the Octane for free was also a bonus...if you exclude the 2 year wait..

Thanks for this. I appreciate the heads up. I’ve not started pricing suppressors yet – but I don’t expect price of the suppressor to be a limiting factor on the decision. It might mean a bit of extra saving time before buying it. I’m finding options that appear to have enough throat for the .350 and are rated for use with a .338 Lapua – so I’d like to think that they’ll be OK with the .350 Legend. Thanks again for the pointer.

Any blowback round you use in an AR could have issues. Most issues have been worked out on the 9mm since Colt had the 9mm sub-gun on the AR platform, mags BCG, buffer weight and springs, piece of cake.

I started my 45 build before any were available and played for well over a year. Clyde was correct in one respect, actualy it was his bolt that made mine and RJ’s guns run. The mags were a different issue that added additional problems. We only solved the mag problems after we got the guns running reliably. There also seemed to be an issue with the particular lower and the Bolt. Mixing and matching gave different reliability.

In any case I have on CMMG rotating bolt AR45 and on straight blowback AR45 that both run, suppressed or not.

Other builds; I like the 300 blackout, (originally 300 whisper). I know the guy that designed it and I know what his objective was. It aint a long range deer cartridge. The ballistics with heavy bullets are about the same as a 45ACP. With a good can it is very quiet when loaded subsonic. I have one with a 10.5” barrel and I use an older model YHM suppressor, rated down to an 8” barrel and MGs, on it. That work great.

On to big bores, I also have a 458SOCOM that I’m still playing with loads on. I have it relatively quiet in a 10.5” and a Hybrid 46 can but I think I can do better with accuracy and different bullets. Advantage is it uses standard AR mags, some feed much better than other, Hexamag being one that feeds great, and it uses 45-70 bullets of which there are a lot of choices. I just haven't taken the time to play with this enough but I like what I see so far.

Thanks sir… I’m pretty sure that I’m going to end up with something smaller than the truly big-bore stuff (as I noted above – I’m pretty sure I’ve eliminated all the pistol calibers). I may end up building an upper in .one of the 450 ish calibers later – but bump in subsonic energy is just not enough to get me over the loss of capacity.

If your goals include running it suppressed with sub sonic rounds, 300 Blackout is the only real choice. An argument could be made for 45acp as well, but getting an AR platform to reliably run 45acp can be difficult...more so than 300 Blackout. Granted, nothing with a suppressor on it is going to be "hearing safe" inside a hallway...might want to add some electronic hearing protection to your nightstand setup.

Another option is the CMMG Banshee in 10mm. Using 200 grain projectiles, it can be subsonic. When using +P ammo like CorBon or DoubleTap, you can get incredible velocities and good performance 100 yards or further. Then there is the magazine compatibility with a G20 carry piece.

Thanks for this. I’ll take a look. At a glance – if I only had pistol cartridges in play this has a lot of upside. Looking at the Buffalo Bore 10mm +p 180s it looks like in the longer barrel (9.5 ish vs true handgun barrel lengths) it might be a real monster.

Thanks!