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