44 if you think a flat profile Winchester soft core jacketed 357 mag pistol bullet driven close to 2000 fps can hold up to the friction from the air as loads approach 2000fps, try some for yourself.
I guess I'll have to. The bullets I used were Remingtons and they held up fine to 100yds launched from a Marlin carbine at 2200fps.
Until they hit something. (anything) THEN, they blew up
Simple point of fact, not every bullet is ok at every speed.
The problem is that 125gr JHPs are optimized for self defense at the speeds found in most defensive handgun barrel lengths, and the carbine adds some 500fps give or take and that goes well past the upper limit of the bullet's controlled expansion velocity range.
JSP 125s might do better, I don't know. I do know that 158s, driven into the 1800fps range do much better penetrating and holding together.
Apples and oranges. The .300 Blackout is a rimless bottle necked .30 caliber 55,000 psi cartridge. The .357 is a rimmed strait wall .35 caliber 35,000 psi cartridge.
ONE load with a 125gr bullet from a carbine length barrel happens to have the same approximate velocity. Other than that, they have little in common