I've also been tinkering with an '06AI using Lapua brass and after 4-5 firings I'm not seeing any doughnut issues. That's using 215 hybrids with no more than 58.5 of H4831SC.Brass was a P.I.T.A$$ BIG TIME! It would develop doughnuts so quickly and so severely that they literally has to be cut out after EVERY firing!
I had a 30-06A.I. that I used for F-Open. Let me explain what I had and what I experienced. It was built around a B.A.T. Model M action with a Shehane Tracker stock. It sported a 30" 1-10 Krieger 4 groove with conventional rifling. I tried the 200gr Hybrid, the 200/20X, the 185 VLD's and the 185 Juggs. I tried H4350, H4831SC, IMR 7828, RL-16 and RL-23. They all shot good with one major caveat>>> they NEVER shot consistently. Brass was a P.I.T.A$$ BIG TIME! It would develop doughnuts so quickly and so severely that they literally has to be cut out after EVERY firing! The "ballistics" were great! I would have even put up with the doughnuts IF I could have got consistent accuracy out of it! However, that goal was as elusive as setting a national record in 15M.P.H. "switching" winds! So the conglomeration of PITA brass (I don't blame the brass itself>> I think the brass flowed easier from a long case body) and inconsistent accuracy brought my project to a sorry conclusion. You might say "Well you had a bad barrel" >>>>If I did, it was on two barrels! Both barrels acted exactly the same way! No more "long" cases for me!
I was using Lapua brass.. It MIGHT be from the 40degree shoulder? I am not sure..What brand of Brass were you using ?? - I've found the Lapua Brass quite good and not to have the problems that you mentioned.
I had it with 2 lots of brass. I was running moderate loads with all the powders I used..I've also been tinkering with an '06AI using Lapua brass and after 4-5 firings I'm not seeing any doughnut issues. That's using 215 hybrids with no more than 58.5 of H4831SC.