I truly hate to hear of this KB. :( I'm glad the OP is OK.
I have a G20 and have never fired a round down the worthless stock tube. Glocks would be much better pistols if you could option out of having to buy there worthless barrels with the pistols. I've seen enough Glocked brass to last me a friggin life time. With most of that being retail ammo. The thought of reloading much less pushing max reloads in a Glock tube is the sort of thing Hollywood could make horror flicks out of.
My G20 has a 5.15" LW barrel in it. Feeds and chambers fantastic! Don't need any of Glock's sloppy chamber characteristics to ensure the pistol is reliable. Much less there awful support.
I shoot max loads and above with my G20 and LW barrel. Brass always looks great! I don't get concerned over flatten primers. I do get concerned... Very concerned over primers with no dent in them or flowing back into the striker slot in a Glock. Your then running up against a very big problem. And if you have a Glock pistol or load in said pistols that swipes the primer you got a big problem.
I do all my initial work ups with Fed primers. There soft and easy to read. Once I get in the neighborhood I then switch to Rem, CCI or Win primers for the fine tune. And stock up on those rounds.
And for goodness sake's folks. Get a set of check weights. This is so important. I don't care what style or price range your scale or scales are using. You have to have check weights and use them. They will save your bacon when you start pushing and going nuclear! They help to keep your scales and your self honest.
As for the load and powder? I've seen AA7 do some strange things when you push it hard. Some strain gauge testing many years ago showed me some ugly 2nd and 3rd wave pressure spikes. It tended to go whacko when pushed. And i think the OP just experienced some of those whacko psi spikes in a useless OEM Glock Barrel.