[stagpanther]

Welcome to the Grendel! A great AR hybrid--but a "finicky" one--don't worry as teething issues are fairly common. I've built 4 of them--I've found that a 16" barrel handicaps the ballistics somewhat--I would go with at least an 18" barrel--but if you're not using it for anything beyond short range hunting it should still be plenty accurate. It was developed around the 129 sst--not surprisingly those bullets tend to excel in a Grendel

The Grendel case typically stretches a bit in use--expect some head bulging and flow when running warm loads. For this reason a full length small base AR die is essential (unless you want to run a high-end adjustable comp die, this is one instance where I could see springing the extra bucks for one) Get a case gauge so you know if you need to knock the shoulder back--I find that you almost always have to with spent Grendel cases from warm loads.

ASC and PRI mags have worked well for me. Cavity back and Alexander Arms produce "Cadillac" magazines for the Grendel. Because the Grendel has a relatively long-seated bullet--sometimes the bullet won't get the necessary lift from the feed ramps before the bullet actually clears the chamber face--so that sometimes--actually pretty often--can cause friction damage and even jams upon feeding. Do a slow-feed of a cartridge from the mag to see if that might be happening. You might also need to adjust the feed lips on the magazine in order to get the necessary "pitch angle."