Borden rifles offers this caliber in their custom rifle.I call to inquire about it and they explained that it was a .300 Weatherby with the radius shoulder blown out to a 35 degree shoulder and that it increases powder capacity about 4%.Could anyone elaborate on this round?What kind of velocity could be expected from a 25"-26" barrel.They said that they are shooting 180's around 3170 fps.This would seem like a very mild load.Do you think it would be worth the trouble of fireforming?
Thanks,
Jim

The idea of changing the shape of the Weatherby shoulder isn't really to gain velocity, rather it's used to insure proper and consistent headspace on a chambered round --- promotes accuracy while maintaining the velocity.

The famous Weatherby velocity claims were mostly shot with longer barrels but in the real world very few realized the published velocity and there isn't anything really to be gained by trying to squeeze an extra 100-150fps with the 180gr 30-cal. bullet.

Jim, years ago I chronographed some factory
Wby 180gr ammo and my velocity was 3055fps in a factory rifle (1/12 twist). Last year I chronographed factory 180gr ammo for the 30-378Wby 3481fps and for the 300RUM 3279fps.

Wby claim to fame was the freebore if with todays powders/barrels you elimate that decrease powder by 5% appr you can get the same velocity maybe alittle more. If you blow the shoulders out increase case capacity by 4/5% you get what the 300Wby was really suppose to do or close to it.

I don't think close to 3200fps is slow for the 300 Borden Caribou. With Nosler,Hornady etc making 300Wby brass alot of things going on with the 300Wby case.

I just had a 300Wby build used a Lilja 1/11 twist barrel set the headspace on the shoulders it was throated for the 180/200gr A-frames and I'm hoping for over 3100fps with 180gr bullets. I got that rifle last Fri so haven't done much as to chronographing loads yet just got the barrel broke in.

Only reason I didn't do the Borden case just didn't feel like blowning cases out kind of getting lazy in my old age and since I also like the 300RUM case. Well good luck.