300 Blackout AR Pistol Cycling issue

[LuckySG]

The spring seems to be a relatively standard carbine spring with about 37 coils (+/- 1 or 2, depending on how count them) and the buffer weighs in as a standard carbine buffer at 3 Oz. I thought about maybe trying a lighter buffer or spring, but not sure which would be the better to swap. I'd lean toward a lighter buffer before spring, but not 100% sure which would be better or if both would be needed.

Approaching this from the perspective that more buffer mass will slow the bolt and a tighter spring is a brick wall (my opinion) which supports the buffer. (Monkey with the buffer first!).

 

[ELRShooter]

Your BCG could be going back too fast to pick up the next round. Watching the ejection angle will help you figure that out. Essentially the gas hole in my barrel is larger so the gun is over gassed. The heavier buffer and spring slowed down the BGC so it could pick up the next round.

I got the adjustable gas block on and had to get a straight gas tube since it sits a touch higher.now all is fine. I can adjust the gas flow for the round. Just need to get a longer Allen wrench now.

 

[LuckySG]

You're thinking that maybe the gas block is offset from the gas port a bit, thus making the port effectively smaller? I guess that could make sense, but the same problem appeared across all four AR-pistols (which I guess is possible if the manufacturer is off in their process... at least they'd be consistent. hehe).

Bingo!

 

[Skier]

Your BCG could be going back too fast to pick up the next round. Watching the ejection angle will help you figure that out. Essentially the gas hole in my barrel is larger so the gun is over gassed. The heavier buffer and spring slowed down the BGC so it could pick up the next round.

I got the adjustable gas block on and had to get a straight gas tube since it sits a touch higher.now all is fine. I can adjust the gas flow for the round. Just need to get a longer Allen wrench now.

I don't think mine is going back too fast. I took some high speed video, slowed it down, and watched the BCG, and it doesn't come back far enough to get behind the next round... I probably stops moving reward about 5-7mm too soon, so the next round never gets a chance to pop up in front of it and get stripped.

 

[matts]

Before one spends more money on parts....
don't want to beat this one up.....
Try some oil.....
Dry BCG bad.

 

[Skier]

Before one spends more money on parts....
don't want to beat this one up.....
Maybe try lube on the BCG and Bolt lugs. Wherever you want. Worst thing that can happen is a little extra cleaning after trying it.

Agreed. Makes sense. (Although I'm not trying to spend money on parts yet... Working with the company that I bought it from to get it to work.) I'll definitely try some lube, if for no other reason that I'm an extremely curious person.

 

[saxon]

So you're proposing that a heavier buffer might help in a 7.5" 300 BLK barrel? That seems counter-intuitive. Other than the obvious experience that it seems to work you, any idea how that makes sense or works?

Maybe your gas port is larger, so your was more gassed than mine, I guess, but if I'm not getting enough reward motion to get the BCG behind the next round on the mag, it sure seems like a heavier buffer would make it even worse. Do you have a link to this recommendation, so I could read it and understand the setup they're using?

if you have a 3oz buffer and you have cycling issue measure the gas port and or light buffer and hard spring meaning ftf

 

[Skier]

if you have a 3oz buffer and you have cycling issue measure the gas port and or light buffer and hard spring meaning ftf

FTF?

 

[Twodogs]

That's not too bad. What make/model are you running? Link?

it an SLR gas block.

 

[saxon]

faile

FTF?

failure to feed, sorry

.099 pistol gas it should cycle on an 8.5

 

[v0lcom13sn0w]

i have had to enlarge a couple 300blk gas ports even with pistol length systems. figure out what the biggest size drill bit fits and go 1 size bigger. no big deal.

 

[v0lcom13sn0w]

i wanna say i used a 7/64ths bit which is .1094"

 

[v0lcom13sn0w]

i started a thread on something similar a few years back about a 5.56 build i did for a friend with parts he provided me. anyway post 14 was the solution and ive done the exact same thing for 300blk with a pistol length system.

AR15 Build issue. gas?

Hey guys, First and foremost, i have built many AR15 type rifles and am no stranger to them at all. i have never had any problem with any rifle i have ever built. i have mainly built rifles with 16" barrels with carbine or midlength gas systems and a couple short barrel pistol builds with pistol...

www.northwestfirearms.com

 

[BPOR11]

i have had to enlarge a couple 300blk gas ports even with pistol length systems. figure out what the biggest size drill bit fits and go 1 size bigger. no big deal.

What increments in your index for one size bigger?

 

[v0lcom13sn0w]

What increments in your index for one size bigger?

i went 1/64" bigger

 

[v0lcom13sn0w]

from about 3/32" to 7/64" i dont have the sizes inbetween which are #41-36

 

[ilikegunspdx]

No buffer tube on a piston gun? Where does the BCG go? I've never worked with a piston gas system, so I might just be ignorant, but I'd think the BCG would still need to cycle and go back somewhere... No?

I haven't been browsing the 300BLK options. I know there are lots of 556 options though. Just ordered the 10.5" BRN-180 (aka stoner's AR-18) for 223/556. Here's a pic of a brn-180 pistol w folding brace fyi (from internet, not my gun):

One example of a bufferless 300BLK fyi:

 

[Skier]

I haven't been browsing the 300BLK options. I know there are lots of 556 options though. Just ordered the 10.5" BRN-180 (aka stoner's AR-18) for 223/556. Here's a pic of a brn-180 pistol w folding brace fyi (from internet, not my gun):

One example of a bufferless 300BLK fyi:

Interesting... It must have a really short BCG and use gas to push it back AND gas to push it forward again?

 

[v0lcom13sn0w]

Interesting... It must have a really short BCG and use gas to push it back AND gas to push it forward again?

probably a really short bolt riding on two rails with springs in front and back likely similar to a sig mcx

 

[Skier]

As I'm thinking about how to respond to Mfg for next steps (and they still have 2 of the 4 uppers we bought, awaiting my feedback, which will be "still doesn't cycle"). Here's my thoughts on options:

(I'll still try with some lube, just to see, but I don't want to close the door on Mfg changes just yet.)

Lighter Buffer: The quick/easy/reversible one would be to suggest they try a lighter buffer, but given that they're already using a standard carbine buffer (3 Oz), I'm not sure if I should go much lighter or if I did, would it be some custom fancy thing that might be a cost-prohibitive upgrade that they couldn't just swap out for "free."

Softer/Shorter Spring: I didn't think that would have much bearing on the issue I'm having and could affect consistent "going into battery and bolt locking."

Gas Port Enlarged: They could do this, but if they do, there's no going back, and although I've never purchased a gas block separate from a gun, I suspect that just about any adjustable gas block is going to be notably more expensive than a non-adjustable gas block, so I doubt they'd throw that in with no additional cost either. If I could talk them into enlarging the port AND installing an adjustable gas block, what would people expect as a fair upgrade cost?