AR Pistol issues

[rumlover]

ISSUE RESOLVED with a heavier spring and buffer.

Gents,

Need some advise. I picked up a 300W upper and I can't get the damn thing quiet. With the can it cycles, is very accurate for it's size, and is getting the right velocity...BUT, it's very loud and is putting a lot of gas and crap back in my face. The sound is definitely coming from the ejection port or chamber area and not the muzzle.

Is it possible that the standard H buffer is not heavy enough to keep the bolt locked, allowing it to open before the bullet and burning powder have exited the barrel (thereby allowing that crap into the upper reciever)? What else could cause these issues?

Specs: 8.5" barrel, pistol length port of unknown size, standard BCG, H buffer and factory rock river buffer spring for their pistol lowers.

Thanks,
Rum

[fasttwist]

Adjustable gas block?

[rumlover]

No, it isn't an adjustable block.

[fasttwist]

A bolt carrier weight may be in order also.

[Titleiiredneck]

Pri gas buster, or silicone around the charging handle,you can also mill the forward assist to blow gas out. The shorter the barrel the louder it will be due to unburnt powder, especially when suppressed. Sounds like you need a weight added to your bolt and a adjustible block also.

[rumlover]

I'm using a pri handle. Compared to the 9" sussressed I heard last weekend, its not an issue of expectation management, but one of mechanical consequence. I just need to figure out whats going on.

[rumlover]

How do you add mass to the bolt?

[TCCrewchief76]

Are you using a high gas volume powder? Wondering about that in a short-barrelled AR...

[rumlover]

10.6g of 1680 with a 225 BTHP = 1080 at 60 deg/29.9 mmg/450'/67% humidity. Same load in a 9" AAC upper was drastically different. Also tried some other powders, but same results.

I've got a H3 buffer inbound now. Hopefully that fixes the issue. When I chrony the rounds, I'm not getting a drastic spread of velocities and accuracy is holding between 1-2 MOA depending on the load. That tells me the bullet is leaving the bore before the bolt unlocks, but not before the gas pressure completely drops.

[Alleycat]

http://www.midwayusa.com/Product/598476/tubb-ar-15-cws-bolt-carrier-weight-system

[rumlover]

Thanks, I'd never heard of that product

[rumlover]

Update...

I changed the spring with a stiffer, RRA carbine spring (stronger spring than DPMS/Colt). With the H buffer, I got a little blow back, but no where near as much as with the lighter carbine spring. When I added a 9mm, 6.5oz, buffer, it completely stopped the issue.

HOWEVER...now it's too heavy to cycle the loads I had out for testing today. I didn't bring any of the AA1680 with 10.6gr and Hornady 225's that I had been shooting because they have been exiting the bore in transonic speeds in both the 8" and 16" barrels I've got on the AR's.