I heard and have not tired yet, that you can make 257 weatherby brass by full length sizing 7 mag brass and fire forming. has anyone tried this how did it work? Thanks.

Let me clairfy a bit you run a fresh 7mm mag brass through a full length 257 wthby die and fire form. The source told me he has been doing this for years. And had no problems loading hot loads.

According to "The Handloaders Manual Of Cartridge Conversions" one can use a .300 H&H or .300 Wby. Mag. case, but itdoes not mention the use of the 7mm Rem. Mag. case. Give RCBS (1-800-533-5000), or Sierra (1-800-223-8799) a call and let us know. Good luck.

Guys the Weatherby's are based on the 300 H&H. Why would you use a 7 MM REM MAG?????? Tom.

Although I haven't tried this, it looks like it would work fine. I might use .264 Win Mag brass instead of 7 Rem Mag, though. Less working of the neck. The .264, 7 Rem Mag, and .338 Win Mag all share the same case dimensions - with the exception of the the necks.

Only area of bad news is that the overall length of the case is going to come up a little short - not a real big deal, since the .257 has plenty of neck length for bullet diameter anyway. And, over time, you are going to get some erosion in theneck areaof the chamber that is exposed to the hot gasses. This could cause a .257 Wby case to extract a little sticky if you had shot large quantities of fireformed .264 Win Mag brass in it previously.

Thanks for the respnonses. And the reason I would use the 7 mag brass over the 300 h&h or 300 wtby is to save money otherwise I would just buy 257 brass.

Roskoe-ya learn something new every day. I did not know the 7 mm Remmy was based on the 300 H&H. Or that the 264 Win Mag could be formed into the 7. I thought the 7 was a proprietary cartridge, and newly developed. Thanks, Tom.

7mm Remington Magnum Brass to .257 Weatherby...

Easy Japanezy. I do it all of the time. One quick pass through the .257 sizing die and you are ready to go. As mentioned before the neck is slightly short, but you get variances in neck lengths all the time anyway...shoot a batch that is at max case length, then trim them back .020" and shoot them again until they grow to max case length again. Case length is never a constant unless you trim them to the same length every time...even then there will be variance.

One thing you do need to consider however is case capacity. In my experience I have to back down about a grain of powder from the loads I had previously worked in Weatherby/Norma brass.

Now lets see...7mm brass 35 cents a case vs. .257 Roy brass at a $1 a pop. I'll take my chances on short necks.

i've done it for my brothers gun.he shot one ragged hole with the loads

ziggy222 what powder/bullet are you using? an