Shoulder Angles .......What's good. What doesn't matter?

[Brinky72]

Another thing to add to the confusion. I recall when I was younger my dad owning and having issues with his Winchester M100 308. Due to it being a semi automatic 308 and the time frame when he owned it, I believe the powder he used was a faster ball powder that burned dirty. He couldn’t find a way to thoroughly clean it and the carbon built up in the chamber and the spent case would hang up. Almost like a self locking taper in the chamber. He couldn’t find a bore brush that he could get in the chamber and scrub the carbon out without tearing the entire action down. I think he resorted to brake parts cleaner and WD-40. A can each per cleaning and,eventually selling it for a 280 Rem 700 Mountain Rifle. He wasn’t the only one with that problem as the local gunsmith kept busy cleaning M100’s. When the 308 came about in the fifties it had a sharper shoulder and less body taper for the time and showed feeding problems in semi automatic rifles when using some common powders even in the late 70’s and 80’s.
My point: I think we have a lot to thank to powder development for the reasons we can get away with sharp shoulders and little body taper in our cartridge design. Add to that modern processes in gun building and we can get away with murder. Take the 6.5 Creedmoor back to 1950 and chamber it in an era semiautomatic burning the powder of the day and it would quickly be a single shot and the most hated cartridge ever made.

 

[Dwh7271]

I have found that accurate rifles can be built in virtually any action, cartridge or barrel length as long as the barrel is properly cut, throated and mounted, the bullets are concentric and the assembly of the cartridges is consistent.

I have to think that’s a very good answer.
To the OP’s question.
Scotty gave the answer on the 40 degree shoulder. Supposedly less burn in the throat although plenty of us have seen fire come out of barrels in the dusk. :grin: So who knows? Less stretch for sure. You sure don’t trim 40 degree cases much if at all.
It seems some pretty good cartridges have gone the 30 degree route.
If it were me, I’d check out some of the cartridges that seem to be used for accuracy uses or have been historically accurate. The PPC’s, 6 BR, 6.5x47, Creedmoor, 250 Savage, 222 Remington, 308.