Best set up for 300BLK?


Wanting to build a 300 blackout AR. Can’t decide between pistol or rifle. SBR is out, don’t feel like going through all the paperwork/hassle with the ATF. I know a lot of people build pistols to suppress them because of the subsonic round capabilities, not quite sure if I’m gonna go for a suppressor either though. Is there a preferable gas system length for 300BLK? Anyone who has experience with the round I’d appreciate any input you have :slightly_smiling_face:


Here is my $0.02 on it…
I own one 300 blackout… and it is a bolt gun. Suppressed.
The reason why is because it has been y experience that things that look exactly a like will get mixed up…
You mix up a 300 with a 556 and you made a mini grenade.

With that being said, pistol length works great. I prefer those 10" barrel units and then get an adjustable gas block. Unless you run piston, then get an Adam’s Arms.


@Jastrzemski223 my first blackout build was years and years ago, long before it was even demonized as the new kid on the block. i was a fan of the 300 whisper at the time. to answer your gas length questions… pistol length, no doubt there. as far as rifle or pistol profile that sort depends on what you want to do as far as profile length, “stock”, etc. a pistol does sidestep the NFA while still allowing a reasonable overall length once the suppressor is attached. but i have yet to shoot with a brace that i like. so i have always went with a SBR. as far as barrel length goes, there isn’t much advantage to anything longer than 10" as far as the round goes, even when talking 110 and 115 grain supersonics.


I’ve got multiple .300blk guns. For your first one, I’d go with a pistol setup. Anything in the 8”-10” barrel length should work fine for you. As has been already stated, anything over 10” is not beneficial since all the powder will be burnt in that space. My thoughts would be to get one with the intention of eventually running it suppressed. That’s where the .300blk really shines. I know money can be a big factor in that decision, but you won’t regret it if you do it; even if it’s awhile down the road.


I built a 16" rifle. After I built a 8" pistol I sold the rifle. The pistol is just so much easier to get around with here on the farm. I will probably surpress it eventually. But till then it is just fine as is.


To me all semi autos are a bit disappointing sound wise with 300bo. The action is just loud. My favorite quiet time gun is my little handi rifle. With the right can on the end its just a quiet pfft and steel ringing. I do run a 10.5 300bo and have had issues with it on certain days depending on weather sending my subs trans or super sonic. I’m not the first to see this issue so I just ordered an 8.2 rosco barrel. That should help keep everything subsonic


This was about a 2k build


10 inch pistol, check out the SBA3 brace, best of both worlds.


Seriously depends on what you want to use it for.
In the subsonic platform it really shines as a suppressed pistol round on steroids (think CQB, or home defense). In this case I’d go with a pistol build.

In the supersonic realm, it can be a direct competitor to the AK47 with better accuracy potential and better bullet selection for hunting etc. In this case I’d go for the rifle build.

I ended up doing both pistol and rifle. One for hunting and one for home defense. Both run pistol gas systems. My pistol is a 10.5” barrel and my rifle is running a 16” barrel.

They’re both fun to shoot, and either one can be used as a range toy.

As for mixing up ammo…always pay attention, keep them separated. All my 300 Blackout stuff is color coded in FDE. I have FDE furniture on my guns, and they run FDE mags. Anything FDE in my current loadout is 300 Blackout.

There are other ways to do this. Just have a system that works for you and stick with it.


That is effin badass right there!!!


Sounds like pistol is the way to go. It’ll be mostly just a fun range toy. Only reason I thought about going rifle length is I already have a full rifle kit for a 5.56 AR so I would only need to swap out the barrel on it. Maybe I’ll just leave that one how it is and build the 300blk pistol over time.


I like the 300blk in pistol form and run subsonic unsuppressed. The blast is more manageable than any other rifle caliber short barrel AR I’ve shot. As stated above though get different mags and possibly even color for the upper so you know at a glance what round it’s for.


A blast diverter helps with the concussion, and a certain versions even assist with the chambering of finicky rounds. I recently put a KX5 on a build. Mine is a 13.7” made to a 16.2” OAL


I have both…556 and 300 Black out. I have 6 mags for each full and keep them separate. I alos have magazine bands on the 556 mags . You can feel them in the dark as long as you remember what has the bands, I use 556 bands on my 556 and nothing on the 300 mags. Something like this. I got mine from ebay cheap.


I use 20rd mags for 300Blk and 30rd mags for 223.


Definitely go pistol form factor and gas system. I built this one a few years ago and couldn’t be happier with the end result:


Nice build


I’m seconding the earlier posts. A pistol length gas system is the answer regardless to barrel length. A certain company (who’s name rhymes with BSK) built carbine length uppers for a while without anyone knowing that it requires a change in buffer spring to make that function. I don’t build .300BLK’s on anything but pistol length gas systems. Makes solving gassing problems much easier.


I SBR’d a 300, with pistol length gas system. I shoot supersonic exclusively now. I was going to try to get a suppressor, but that’s fallen down to the lower half of my “gotta have” list. I put a Strike industries PDW stock on it, but will probably reconfigure it with a MFT minimalist stock. It’s it bit more comfortable to shoot.


My small frame .30cal collection.

  1. 16” DI 7.62x39
  2. 16” (OAL) DI 300Blk 13.7” “Dissipator”
  3. 9” Piston 7.62x39

Sorry for the first pic. This second one shows the upper as completed