6.5 Grendel Pistol Issue

[wideglidejoe]

I've recently put together a 6.5 Grendel pistol upper, using a 12.5" Ballistic Advantage barrel that I purchased from Granite Ridge, along with a 6.5 Grendel bolt & carrier. I already have a 10.5" 5.56 pistol, I'm swapping the two uppers between the same pistol lower. The 5.56 runs perfectly, in all ways. I wanted the 6.5 Grendel pistol to go with my Alexander Arms 6.5 Grendel rifle upper, which I love. I've put maybe 30 rounds thru the 6.5 Grendel pistol upper, with some issues. It fires OK, it ejects the empty brass to 3-4 o'clock, resets the trigger (Geissele S3G) for the next shot, but "short cycles" or whatever you want to call it, without loading a new round. I've tried three different mags, two different 10 rd AA mags, plus a 30 rd E-lander, all three of which work fine in my 6.5 Grendel rifle, so I don't think its the mags. One friend tells me I've got gas issues, either the gas port isn't lined up correctly or gas port isn't big enough, others tell me its a buffer/spring issue. I'm using the standard carbine buffer & 10.5" spring, which works great with the 5.56 upper, even when running very fast with the S3G trigger.

Any suggestions which end to start on? Gas port size, gas block alignment, or buffer &/or spring?

Thanks in advance!
Joe