300 BLK Crushing Brass on a New Build

[Badfinger]

Try to cycle some factory rounds first, your case neck looks a little large and may need some more crimp. Check it against a known good factory round. Good luck.

[WalterGA]

What brand barrel is it?

My question, also. The feed ramps don't look too bad. Maybe a little honing and taking the corners off of the extension @ the mating of the receiver would help, but I'm betting it's the reloading methodology.

FWIW, nobody @ SOTA barrels has a clue what M4 feedramps are. I bought two 5.56 barrels from them that came with rifle, not M4 extensions. The second barrel was to replace the first, as the first clearly didn't have M4 ramps. I sent pics similar to the OPs, showing a pronounced ledge where the extension meets the receiver cuts. SOTA said they couldn't tell from my picture if theirs was an M4 ramp or not, that they needed a "side view." I knew right then that they didn't have a clue! Fortunately, a friend who'd recommended SOTA bought the second barrel from me @ a slight discount.

[Trinimon]

Are you crimping those reloads? You're not adding flare are you?