So I went to the range today with a new set of development loads I was very hopeful for. I ended up getting to shoot ten of them, then driving home to the bullet puller. My rifle is self-built with a 20" 1:8" twist AR Stoner HBAR barrel with Wylde chamber and a syrac ordinance adj. gas block. The loads were brand new FL sized .223 Rem Winchester brass (that I heard good things about and then was disappointed when the standard deviation of case weight was about 3 grains.) with Win. small rifle primers and 77gr SMKs. Charges were 23.0, 23.4, 23.7 and so on up to 24.1 gr all Reloader 15. OAL were EXACTLY 2.260 on all of them. (24.1 was the max load listed by Sierra) so I shot the 23's, no problem. Nice group at 150 yds. I had my gas block closed as not to loose brass in the cornfield. No pressure signs at all, so I move to the 23.4's. First shot upon inspection has a mildly flattened primer. Hmm. Second shot sounds fine, but on the case I find a .75" crack right down the side and flattened primer. (***?) 0.7 grains under max and I have a case failure. The other three also showed flattened primers. No extractor marks. No cracks. I didn't dare move up. Maybe some brittle cases? I'm so dismayed. Any advice? (other than keep all loads at 23.0 gr now?)