300 Blackout

I was recently contracted to build an upper in 300 Blackout. Normally that wouldn’t be a big deal. 18″ mid length gas. No problem, right? Now enter the JP Enterprises adjustable gas block. The fit of the gas tube into the block was tight enough that I had to tap it in with a non marring hammer. Before you get excited I like that. It didn’t need to be quite as tight as it is but I’ll take it. That tight of a fit ensures there won’t be any gas leaks around the gas tube. Ok, so +1 for JP.

Many adjustable gas blocks have the adjustment screw as well as a set screw to ensure you don’t loose your adjustment. The JP block isn’t one of those. To top it off the adjustment screw is actually loose and wobbly. Not good. You can adjust this one by hand…no tools required. This also is not good. What it means is unless you use copious amounts of locktite on this screw you will be getting a big gas leak. Well after buying two boxes of ammo from the only local shop carrying 300 Blackout at $25 each….I do indeed have the aforementioned gas leak. Ok, now I’m a little ticked off.

So I go home and call JP Ent. The guy answering the phone didn’t know anything about them and said I’d have to talk to the engineers. Ok, you don’t have any gunsmiths, or certified armorers on your staff so for technical help I have to go to the design engineers? Since you sell complete rifles that’s a little messed up. Well, it just so happens that they were all out at lunch so I left a voice mail.

Two weeks later I get a call from the engineer….two weeks. All he can say, on his phone that keeps breaking up, is “have you gotten it to work yet?” Seriously, dude? Come to find out they haven’t been able to get their adjustable gas blocks to work with 300 Blackout with anything but a long 18-20″ barrel with a PISTOL GAS LENGTH with the gas port on the barrel drilled out to the same size as the hole in the gas block. That’s a 1/8″ diameter hole. I don’t even know where to begin commenting on that without cursing. I really don’t.

Ok, in defense of the round, 300 Blackout is meant to be suppressed. They took a 5.56 casing and blew it out to 30 cal. This is a low pressure round. That being said there should still be enough gas energy to function the weapon. “SHOULD”.

So, I have a regular Yankee Hill low profile gas block on this upper now. The engineer says he would like to know if the weapon functions with a normal gas block on it. In all reality…it shouldn’t have a problem. It will no longer be hemorrhaging gas out the side of the gas block it should have enough to work the acti0n. I’m waiting for less expensive ammo to get here so I’ll update you when I test fire it again.


I should say that I love the JP triggers. Those are awesome. I won’t be using their adjustable gas blocks, however. Not even if a customer asks for it. I won’t have something that low quality on my rifles. You probably shouldn’t ask for JP anything but triggers….lets leave it at that.

2 thoughts on “300 Blackout

  1. Your problem may not be the Gas Block. I just got off the phone with my barrel supplier. After trying to order an 18inch Mid length 300 Blackout barrel, the gal said that I should talk to the VP because of a problem with the design, Per the VP, the problem is that the 300 Blackout does not generate the correct pressures for the weapon to function properly. The AR bolt undergoes a 2 stage process during a cycle. In the first stage the movement of the bullet compresses the air in the barrel ahead of the bullet which starts the bolt unlocking process. In the second stage after the bullet passes the gas port the higher pressure of the burring powder completes the unlocking and pushes the bolt back to cycle the rifle. The problem is that a Mid or Rifle length gas port there is not enough barrel forward of the gas port to insure cycling. They do not recommend anything other than a carbine length gas port.

    1. You’re right. I’ve had the same discussion with my barrel maker. I’m still not impressed with the way the JP gas block was hemorrhaging gas. It actually made the problem worse.

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