.300 BLK PDW Build

https://imgur.com/a/hT58CoG

I built a .300 blackout PDW and had the chance to shoot it for the first time today.

It has a Ballistic Advantage 6” barrel and a Maxim Defense BCG and telescoping buttstock.

I only put 80 rounds through it because I was at an indoor range (40 feet max).

I was surprised by how light the recoil was and how well the stock felt. I fired 40 rounds of 150gr FMJ and 20 rounds of 110gr V-Max without issue. It was very accurate at the admittedly short range I shot it. I also fired 20 rounds of 220gr subsonic, but it failed to feed all of them. It would fire and eject the empty case and cock the hammer, but fail to strip a fresh round from the magazine. My subsequent trigger pull just dropped the hammer on an empty chamber.

I have a .30 suppressor in jail (Deadair Nomad) so all the shooting was unsuppressed. I was running the standard weight buffer from Maxim.

I’m thinking that I have it set up correctly. It fires supers no problem and just barely chokes on subs unsuppressed. I think when I mount the suppressor, it will run fine with subs and supers. I have no plans on ever shooting subs again without a suppressor.

Does anyone have any similar experience with such a setup? Am I thinking about this correctly?

That lil guy looks sweet. I have yet to dive into .300BLK but it sounds like you hit the high points. A little more gas with the can on should have you running those 220s just fine.

I have a couple of short 300BLKs, an 8" SBR that is always suppressed that shoots subs and supers, and a 7" PDW that is always unsuppressed.

For my 7" unsuppressed PDW, I have it setup to cycle both subs and supers without problem, which is how i like it, because i will never suppress that one, so our situations are a little different.

As far as if yours is setup correctly, I would just see how it shoots subs with your can, and then you can tweak it if needed. Having an adjustable gas black makes that process easier.

I personally don’t like to go under 7.5”-8” for subs.

They tend to get finicky without a custom shortened gas system. Only shooting subs with a suppressor is the most likely to work out, and with yours ejecting spent cases I think there is a good chance it will run suppressed.

I also tend to be finicky with less than about 7” of handguard because I can’t use a normal hold. And for me, being able to use it pretty much interchangeably with my other AR’s is the main reason to PDW an AR rather than something that folds up smaller.

What's probably happening with your subs is that not enough gas is coming back. Since the Nomad isn't exactly low backpressure, it will likely provide the force necessary to drive the bolt back far enough to strip and load the next round.

Looks like a great setup! I have a couple blackout ARs, one is similar to your idea here. It was the first blackout I put together when it was finally becoming commercially viable (ie. there was a 300 BLK SAAMI spec, not just the wildcat). I wanted a 7" barrel, but there weren't very many companies with a quality barrel out there, and even fewer offering as short as 7." I bought a 9" BCM barrel and had it cut down to 7" and re threaded. That is a gun I really only shoot supers through, and have a FCD dead air muzzle device for my Sandman. You are right if it's gassed correctly even the supers can shoot soft and I really enjoy shooting it.

This is just my own experience, but I almost treat blackout subs and supers like two different calibers. Yes I know the whole idea is "both from the same gun" and I have done plenty of that, but there is just no way to shoot 110 supers with 20 grains of powder at 50k+ PSI and a 220 sub with 10 grains of powder and under 20k PSI in the same gun with no adjustment and have them both running the gun in an optimum way. I think that is exacerbated with a very short barrel where you need all the gas you can get to get subs to cycle.
Whether it's an adjustable gas block (not ideal for some people), or some other method, I think if you want to run both you need a way to adjust the gun.
If you want to shoot primarily subs or supers, I would set the gun up to work with them, and understand the other option will not be ideal. Currently I have an upper for supers and an upper for subs, and both are tuned to run with the chosen ammo. It's night and day shooting subs in the sub upper, then putting supers in. Sure it works 100%, but gas to the face and recoil are both significantly higher.
The gun looks great, and I still am pleasantly surprised when I grab my blackout how short and light it is, I'll bet yours is similar. Something that short is just really handy to carry around.

Quote:

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Originally Posted by nate89

This is just my own experience, but I almost treat blackout subs and supers like two different calibers. Yes I know the whole idea is "both from the same gun" and I have done plenty of that, but there is just no way to shoot 110 supers with 20 grains of powder at 50k+ PSI and a 220 sub with 10 grains of powder and under 20k PSI in the same gun with no adjustment and have them both running the gun in an optimum way.

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I was making 300 Fireball barrels before the Blackout and did a lot of testing for gas port sizes and cyclic rate with the Blackout. Your thinking used to be a lot more true than it is now.

Night and day difference with the powder burn rate chosen for the subsonic Blackout. Until you get into really short barrels the subsonic and supersonic actually cycle quite closely to each other. You can make some improvement for comfort with an adjustable gas block but I found them to both run reliably without any adjustment.

curious to see what results from the can install. I am about to start this testing on my own and am trying to learns as much as possible before i blow through tons of ammo trying to sort out any issues mine might have.

Quote:

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Originally Posted by nate89

This is just my own experience, but I almost treat blackout subs and supers like two different calibers. Yes I know the whole idea is "both from the same gun" and I have done plenty of that, but there is just no way to shoot 110 supers with 20 grains of powder at 50k+ PSI and a 220 sub with 10 grains of powder and under 20k PSI in the same gun with no adjustment and have them both running the gun in an optimum way.

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My 8" build runs well with all supers and the only subs it has had issues with are ones that weigh less than 200g. Even with those, the issue is that it doesn't lock the bolt back on the last round. It cycles them fine.


I use an OSS HX-QD 762 can, so I just tuned the gun (buffer weight, specifically) to reliably run 200g or heavier subs and I can pop in a mag of 110g Barnes tac-tx without adjusting anything.