Author Topic: 257 STW and 257x300 WINNY (Read 764 times)

Forest Walker · « **on:** January 03, 2006, 01:39:42 AM »

Can anyone give me max chamber pressuers on these two rounds and any other info you may have. I am considering one of the 2 for an upcoming project

Lone Star · « **Reply #1 on:** January 03, 2006, 09:00:45 AM »

There is no SAAMI maximum chamber pressure for the wildcat .257/300 WM. The max pressures for the Weatherby are between 54,000 cup and 63,000 psi. The max pressures for the parent .300 WM case are 64,000 psi / 54,000 cup. It's a wash. Build the Weatherby. One of mine does not have the Weatherby freebore and it shoots very tight groups; you have to cut the listed maximum loads by 4 to 6 grains though.

Yukon Jack · « **Reply #2 on:** January 03, 2006, 05:24:32 PM »

There's quite a bit of info on the STW version at 24 Hour Campfire site. It is a real smoker, but needs a very long barrel (28-30") to take advantage of all that powder coming from a 25 bore.

The 25/300 Winny is practically the same as the 257 Wby Mag and there is plenty of data out there for it. You can push a 100 grain X from the Wby around 3700 fps with a 26" barrel, and 3650 for so from a 24" barrel.

nomosendero · « **Reply #3 on:** January 14, 2006, 03:42:08 PM »

Actually the 300WM case is quite a bit longer (2.620 vs 2.549) plus the
Winnie is alot longer up to the shoulder because of a shorter neck, therefore it will hold a good bit more powder than the 257 Weatherby. The
.257/300WM will run very close to the STW in 27-28" barrels while using
less powder. Check it out on www.reloadersnest.com