300 Black Out build: Which problem first!?

[wally]

I'm just saying, if you've exhausted all the other under-gassing issues you are left with the fact that the port size is too small for ts location along the barrel and the pressure curve of the ammo. The actual measurement of the current port size doesn't really matter -- its either "right" or not. Too large and your adjustable gas block could correct it, too small and nothing will work except opening it up.

Seems you've addressed the gass "leakage" issues and too much reciprocating mass issues as best you can, and are close to running out of things to try.

If you can try "hotter" ammo that could be diagnostic, if it then starts locking back, either stick with that ammo or open up the port a bit. Its not that hard -- I've done it several times using "number" drills, one size larger (lower number) that the largest that fits into the port, I use a pin vice (or a spare drill chuck) and do it by hand as if the drill was a reamer. Only once did I need more than two steps to get it right. No real need to try a new barrel at this point unless its not grouping well.

 

[RecoilRob]

Are you sure the gas tube is unobstructed internally and flowing as it should? A bit of swarf stuck up inside could block enough gas flow to make the problem you're seeing.

 

[HankC]

reloading the empty brass with 180 grain projectiles

180 gr will take less powder and likely worse If your rifle does not lock back on Rem factory 110 gr supersonic ammo.
you said you have adjustable gas block,16" Carbine Gas does not need one, it just add another factor. You can always use a weaker buffer spring. My Classic 16" carbine gas 300 BLK runs well on standard buffer and spring. May wish to check gas leaks. When my rifle was new, I saw trace of gas leak at gas tube to the block. How far it kicks the spent brass? It may give some indication if enough gas.

 

[RussellC]

Adjustable gas block is for later suppressor use. I am pretty sure its a gas block problem. Checking fit into key, and replacing tube and block anyway, always good to have ectra parts if not needed.

Again, from all my reading the existing gas port is oversize, slightly anyway for this type of build. (.125") I have enough spares to try different things, except barrel. If nothing else and it proves necessary, I will replace that. I am constantly building so nothing goes to waste. I suspect the gas block/tube replacement is going to fix it.

Going to use non adjustable for now to get this thing running as it should. Was too busy loading .45 ACP ammo tonight to mess with it. As previously stated, as soon as Brownell's get that Nemo spring back in stock I will also try it, unless it gets fixed with block and tube replacement. I also want to try it on one of my other carbine's lowers, just to eliminate that unlikely cause.

Russellc

 

[RussellC]

Oh, the brass does not eject that bad, but not as strong as my .223/5.56 ARs. They also tend to throw brass slightly forward, this 300 BO throws them at an angle to the rear. Will report back after next range session, looks like rain for a few days.

I really dont think the different lower will help, but I think the gas block and tube replacement will. If not, will replace barrel.

Accuracy is quite good, this is with an inexpensive red dot.

Russellc

 

[RussellC]

Problem solved. It was indeed the gas block. Installed a non adjustable and now it cycles fine, always locks back. It is over gassed now! Will find a high quality adjustable.

Russellc

 

[HankC]

It is over gassed now!

Load too hot or you have weight removed from buffer? 300 BLK 16" Carbine system is not likely over gassed unless you shoot hot load or suppressed. Personally, I'm not a fan of adjustable gas block, I would rather switch to a different weight buffer or spring if I ever want to shoot subsonic or even suppressed. >90%, if not all, of my shootings are supersonic, unsuppressed, no reason to mess with gas adjustment.

 

[RussellC]

Yes, it is still missing one buffer weight, which is going right back in. I was already going to get some heavier buffer weights for other guns and sure will try them in this gun as well. There is a silencer in my future, so a new adjustable may be coming home anyway.
My barrel does have the larger size port, .125"

Good news is, it works like it should have!

Russellc