Building an AR Pistol. Caliber and barrel length opinions needed?

[ScatPackLife]

Like the title says, I'm building an AR Pistol and I'm hoping to get some advice from people who have experience with different calibers and barrel lengths.

Here is what I'm looking at (bullet points for easier reading):
- Barrel length between 7.5"-11.5"
- 300blk, .223/5.56, or 9mm.
- Possibly suppressed down the road but ammo will still be supersonic.
- This gun will probably be my HD gun once I am confidant of it's reliability.
- I have lots of .223/5.56 and 9mm ammo since I have AR15 rifles in 5.56 and handguns in 9mm, no 300blk.
- The AR15s I have I built and I am aware of the AR Pistol Laws so that is no concern.
- I've done a lot of research online but no experience with 5.56 in short barrels or 300blk at all.
- My concern with 5.56 is reliability, blow back, and concussion.
- My concern with 9mm is it's not as potent as rifle rounds.
- My concern with 300blk is ammo cost and availability.


With all that in mind what are your thoughts on what caliber and barrel length would be best for an HD gun and why it would be better than the other options?

Thanks

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[Swiss_Cheeze]

Well right now I think number one would be availability of the caliber you choose.

 

[Swiss_Cheeze]

Then parts. 300blk you can shorten it up. I forgot but you can find it. If 556 I think somewhere in the 10.3 or 10.5 length.

 

[Yotehunt]

224 Valkyrie is everywhere.

 

[Member 34319]

Current climate, 223/556 or 9mm. Anything 300 black right now is bonkers.

 

[arrowshooter]

I would go with the 5.56. As you mentioned the 9mm is less potent, and the 300 BLK is crazy as mentioned above with pricey ammo and long wait time for barrels. You should be able to find a 5.56 10"ish barrel and ammo is running maybe $.50/rnd less.

 

[biggie24420]

I'd go with 10.5" in 5.56. I had a 7" and I never had any cycling issues, but I like the look of my 10.5" better. Also I like being able to shoot .22lr out of my M4 and 10.5" pistol.
I also run a suppressor so it was recommended that I don't go under 10.5" barrel with my hynrid 46 suppressor.

 

[Deerhurst]

8" 7.62 Tokarev? Or am I just being silly?

But seriously, that's the one in looking forward to chopping the most! Gonna be 8" and suppressed.

 

[ScatPackLife]

8" 7.62 Tokarev? Or am I just being silly?

But seriously, that's the one in looking forward to chopping the most! Gonna be 8" and suppressed.

That's actually what I decided to go with. I got an 8" faxon barrel and will be getting a suppressor. Just moved from Cali so Im super exited about getting one.
And 556 just made the most sense since I already have ammo and mags. I will likely build uppers in 9mm and 300blk later down the line.
Thanks for your input everyone.

 

[titsonritz]

Then parts. 300blk you can shorten it up. I forgot but you can find it. If 556 I think somewhere in the 10.3 or 10.5 length.

The 10.3" barrel length is a product of the Crane Mk 18 Mod 0, it is the shortest length barrel possible with the carbine gas system and standard A2 FSB. They basically took the standard 14.5" M4 barrel, cut to 10.3", increased the gas port from .062 to .071 and tossed in an H2 buffer.

The reality is, though, 5.56/.223 really drops off in terminal ballistics at the 10.3"/10.5" barrel length range and the dwell time of the carbine gas system is super tight. This is where the 11.5" with a LPGB and 10.5" handguard comes into play, that additional 1"/1.2" makes a huge difference in both increasing the dwell time, for a better running machine and nice jump terminal performance. IMO, bumping up to 12.5" might be the ultimate compromise for general purpose AR.

 

[ScatPackLife]

The 10.3" barrel length is a product of the Crane Mk 18 Mod 0, it is the shortest length barrel possible with the carbine gas system and standard A2 FSB. They basically took the standard 14.5" M4 barrel, cut to 10.3", increased the gas port from .062 to .071 and tossed in an H2 buffer.

The reality is, though, 5.56/.223 really drops off in terminal ballistics at the 10.3"/10.5" barrel length range and the dwell time of the carbine gas system is super tight. This is where the 11.5" with a LPGB and 10.5" handguard comes into play, that additional 1"/1.2" makes a huge difference in both increasing the dwell time, for a better running machine and nice jump terminal performance. IMO, bumping up to 12.5" might be the ultimate compromise for general purpose AR.

My general purpose AR has a 16" barrel. I also have a 20". This is really more for fun.

If I can get it to run 110% reliable with a suppressor and can find a load that works (ie, need to do ballistic testing) well in the 8" barrel, then and only then will it become a HD gun.

I got an adjustable gas block so hopefully it will run reliable. I have seen a few 556 rounds that work pretty good from a pistol length barrel, still gonna test them before trusting them.

 

[kmk1012]

I built a 7.5" 5.56 AR pistol for home defense a while back. After shooting it at the range I realized it's merely going to be a range toy. It's WAY TOO LOUD for any kind of indoor use period. I originally thought it was going to be the perfect balance between power and capacity but the concussion will cause hearing damage. Maybe it's my muzzle device but I really don't want to wear hearing protection at all times while at home. Just my two cents and I'm sure someone else will chime in otherwise but I'm willing to let anyone shoot mine and say something else.

 

[JakeWidme]

Buy the .300 BLK tools and become a handloader. You can shoot supersonic surplus .308 bullets or cast your own hard cast lead subsonics and save a FORTUNE on ammo. Harbor Freight has the mini cut off saw for the brass, I have one. ALSO with the AR you can change uppers for caliber changes ! 8 inch barrel is all you need

 

[kmk1012]

My 8.5" 300blk AR pistol is my go to HD gun when my suppressor is screwed on it, gotta love that cartridge. Subs are quiet enough to not do hearing damage inside if suppressed, not sure about supers though. My HD is constantly rotating between almost 20 rounds of 45ACP on tap and my 300blk "pistol". The cool thing about 300blk is when you get into bolt action with subs, so quiet everyone giggles and asks if I really took a shot. Not too much louder with the setup on my 300blk AR pistol.

 

[Deerhurst]

I built a 7.5" 5.56 AR pistol for home defense a while back. After shooting it at the range I realized it's merely going to be a range toy. It's WAY TOO LOUD for any kind of indoor use period. I originally thought it was going to be the perfect balance between power and capacity but the concussion will cause hearing damage. Maybe it's my muzzle device but I really don't want to wear hearing protection at all times while at home. Just my two cents and I'm sure someone else will chime in otherwise but I'm willing to let anyone shoot mine and say something else.

Anything will be miserable with walls and a roof. Suppressors help.

 

[ScatPackLife]

Anything will be miserable with walls and a roof. Suppressors help.

Even 9mm.

That's why I am for sure getting a suppressor before I pretend it would work for HD.

 

[ScatPackLife]

ALSO with the AR you can change uppers for caliber changes ! 8 inch barrel is all you need

That's not true legally speaking. 8" barrel upper needs to be on a Pistol or Registered SBR lower to be legal.

I'm from Cali so I know a lot about stupid gun laws. I have 2 AR lowers and three uppers that I built plus an 80% lower that will be for my AR pistol, just bought all the stuff to finish the lower and upper receivers. I'm fairly well versed with AR LEGO's. The only thing that has been keeping me from multiple calibers on the AR platform is money. If I could justify the money I would have ARs in 300blk, 9mm, 45acp, and 556 (and AKs in 762 and 556). And if I could ever justify the money I would own a NEMO OMEGA in 300 win mag, that would be a different lower obviously. I can't justify $5k for a rifle I would only take to the range once in a while and I for sure can't justify $2-$3 a round - and you thought 300blk was expensive.

 

[JakeWidme]

That's not true legally speaking. 8" barrel upper needs to be on a Pistol or Registered SBR lower to be legal.

/QUOTE]

DUH. Please read the OP one more time. You are building a PISTOL. Barel length is not relevant

 

[ScatPackLife]

DUH. Please read the OP one more time. You are building a PISTOL. Barel length is not relevant

You missed my point.