Have any of you ever bought reloading dies that sized the case improperly? I have a set of old Pacific dies that were given to me by a good friend of my dad's for a 257 Weatherby Mag. I reloaded some shells and was getting very serious blowback along the whole length of the case. I suspected the dies were sizing the case too small, so I purchased some factory ammo (I forgot how expensive Weatherby ammo was). No more blowback with the factory loads. Do you guys agree that this is the problem before I go out and buy new RCBS dies? The loads I used ranged from light to hot using RL-22, all resulting in blowback. No primer damage. No sticky bolt.

Jethro if you're getting it below the neck area, then I'd definitely say you're on the right track. It could be the chamber is just a hair oversized and the dies are a hair under, but who knows. Regardless, the solution for me would be the same. I'd go get another set of dies.

I would phone or e-mail Hornady.
If you talk to them "just right" they might just replace their old Pacific dies with then current NEW DOMENTION DIES.
www.Hornady
1-800-338-3220

By "blowback", I assume you mean that the necks and bodies of your cases come out sooty after firing. This is NOT a result of the case being sized too small. After all, you can fireform something as undersized in the body as a .300 H & H in a .300 Weatherby chamber with no such "blow back".

Look somewhere for fault besides your dies. Try a different powder, for example. Sooty cases are usually the result of low pressures or a powder that is too slow for a given chambering. That wouldn't appear to be the case here, since RL 22 certainly is not too slow for the .257 WBY, but do try another powder (say IMR 7828 or AA 8700) before getting rid of what are likely perfectly good dies.

By the way, what weight of powder and bullet have you been using when you experienced the "blowback"?

I used numerous loads of RL-22 up to 71gr with a 100gr bullet. The 117s did the same. It's hard to believe that going to the other powders you mention would possibly fix it. There are many guys using RL-22 that don't experience this. What the heck though, I've got some 4350 I can throw in them to check it. It's a little fast for this cartridge, but should test the point you are making. Won't be able to do it for a while though. Weatherby has my rifle to figure out why it shoots 2"+ groups with factory ammo. They garauntee less than 1.5".