Hmmm I have a 9.5x57 (.375) also which I didn't mention before as I am still fire forming cases for it. But the shoulders really sharpen up and the taper in the case gets blown out so I guess you could say it almost ends up with an Ackley shape to it. I wouldn't think I could shove the shoulder back "slam feeding" it but I haven't tried yet so don't want to comment. But I will be sending it off to get the extractor polished in the hope it will close over a round dropped in as I also get the bolt hold open ground off the magazine follower for this reason. Mainly shoot multiple pigs in mobs so quite often looking for a quick "parting shot" haha
Please let us know how you go, I love to learn more and I do love my 338.06 and don't think it would disappoint you although not many Bears "Down Under"