I had a .358STA as soon as the reamer dimensions were known as well and later built a .375-358STA. I've killed a lot of elk with both. The shoulder is 35 degrees and .502". It is almost identical to the .308 Baer which was around even longer and I've had one for longer (still do). It's the same 35 degree shoulder but .497". The powder capacity difference in basically nil. There is 2-2.5 grains difference between a .30-8mm and either of the other 2. Not enough to justify dealing with fireforming. Anyway right after I had the .358STA built we ordered the reamer for the .30-358STA and we built several rifles. If Kenny was working on it back then you never heard about it. He made a big deal about it probably 2-3 years later after we were already tired of fireforming brass for both the .30-358STA and .308 Baer. He use to actually say it was a .30-358STA back then too. We killed a lot of rockchucks with all 3 versions. That's back when NBT's came in 100 packs, powder ran about 10-11 bucks a pound, and primers were 1.00/100. You could buy the NBT's at SPS for about 10.00/100. We could shoot the big calibers for what it cost to shoot a .22CF today and we shot them a lot. Got a lot of weird looks from people with a 16-17lb rifle across the hood of the truck shooting such a big case for rockchucks. Once they saw on hit they knew why we used them though.
We have wildcated the 8mm Rem. Mag case from 7mm to .458 in every caliber except .404 so I have a pretty good knowledge of it. I still have a .308 Baer, 2 .338 Baer's, .358STA, .375-.358STA in addition to the more standard 7STW, .30-8mm, .416 Rem., and .458 Lott. I can honestly say I've spent more money on reamers based on that one case then any other by far and we have close to 100 reamers between us.
We have wildcated the 8mm Rem. Mag case from 7mm to .458 in every caliber except .404 so I have a pretty good knowledge of it. I still have a .308 Baer, 2 .338 Baer's, .358STA, .375-.358STA in addition to the more standard 7STW, .30-8mm, .416 Rem., and .458 Lott. I can honestly say I've spent more money on reamers based on that one case then any other by far and we have close to 100 reamers between us.