I have been burning up the search button, but have come up empty. I have a malfunction/FTFeed with a home built DMPS LR-308 frankengun. The upper, lower, and mags are DPMS, the barrel and bolt are Fultan Armory (20" Titan barrel). Total rounds through the gun so far are about 300+. All parts were ordered brand new by me and assembled lovingly in my basement.
The malf has two parts. First is that the rounds sometimes (about 1 in 20) hit the front of the magazine which sets the bullet back into the case and makes my velocities go all over the place. I'm worried about pressure problems. I use my own handloads, but they're pretty mild (43.4 grains of Reloader 15 in once fired Winchester cases pushing 165gr SGKs, or 155gr Nosler CC; velocities at 2,585 fps for the 165 grainers). I have tried crimping the cartridges but it does not matter at all. The bullet is jamming in there way far. I have had this happen with the 4 round DPMS mags, as well as the 19 rounders.
The other problem is that the bolt sometimes (hard to tell the quantity as I often load one round at a time into the mag. Load development and all) fails to pick up the next cartridge at the case head, and instead catches it about two thirds of the way to the shoulder. This drives the round up towards the chamber at an angle, not all the way in, and the bottom two lugs of the bolt press down into the case, ruining it. I'll post pics tonight if I get the chance.
My initial guess is that the bolt is cycling faster than the magazine can present the next round. The mags are brand spanking new, but I loaded one of the 19 rounders up full and left it for a week to break it in and it still does it. The buffer and spring were for an "AR-10", which, correct me if I'm wrong, the LR-308 doesn't need the extra length required for the Armalite? Am I using the wrong buffer and spring? The buttstock is the standard fixed buttstock, not a collapsable. I am considering ordering a new buffer and spring from Fultan Armory; maybe it will work with their own bolt? Am I in the right ballpark, or is there something I'm missing?
Can any AR jedi out there set me straight? I would greatly appreciate it.