Have a 7.62 x 40 WT barrel installed now on an AR flat top. 16" stainless, carbine gas, from X-caliber barrels.
The barrel wont pick-up and feed with H110 or IMR 4227 powder, behind a Nosler 110 gr Varmigeddon bullet or Sierra 125 gr Pro hunter. (Using Wislon load data)
It will cycle, feed and lock bolt back with IMR 4198 and the Nosler 110 and the Sierra 125gr bullets, with charges from 20 to 24 gr.
24 gr/ Imr4198 is the absolute max I can get into the case, using a drop tube and jiggling the case to settle the powder.
Haven't had a chance to chronograph the loads yet.
It is pretty obvious that I need to get some AA 1680 powder, as this seems to be the "perfect" powder as to burn rate for this cartridge. AA1680 is "unattainium" every place I have checked. So for know I will use the 4198.
Also, this carbine barrel/upper is being used on a lower with a rifle length buffer/tube stock set up, could this be the fault with under gassed cycling with the faster powders? Is this a mismatch?
I see you can get a lighter buffer for the rifle length stock set up, and was just wandering if this would help with the "under gassed" problem and let the bolt move faster and pick up cartridges from the mag.
Enlarging the gas port hole might be a fix, but I don't want to attempt that operation myself.