GCs don't fit RCBS Pistol Mould

[Irascible]

I have an RCBS 250K and another RCBS for a 38-55 GC bullet, both are great. I was looking for a 357 mould, so I bought another RCBS. I read, where they are sized to work with a 1/20 tin lead alloy and thought nothing of it, other than "that's OK as I will have a bullet big enough when using WW/tin (Lyman #2)". I spent hours casting and eyeballing the results for the best ones. Then I went to size them, the gas check were no where near fitting! Not even close!
Is this a common thing with RCBS pistol moulds? I have another pot with 1/24 BPCRS alloy, and I'll try that later today. It just seems to me that with a caliber that likes to lead as much as the 357 magnum, they would consider sizing for a harder alloy!

[Calamity Jake]

RCBS molds are designed and cut for 100% Lino, or at least the older molds are. That's why they always cast small with other alloys.

If your GC's are to big, try annealing them so they will not spring back. If still to big, superglue works

It's not the caliber that makes boolits lead, it's fit, alloy hardness and excessive speed that can cause leading among other things.

[Irascible]

According to their literature, their rifle moulds are sized for Lino. The pistol moulds are sized for 1/20 - tin/lead. Casting 357 pistol bullets of my Lyman #2 aproximation, The heel of the bullet is way TOO LARGE for the gas checks.

[GabbyM]

Make sure the mold is closing tight. Hold it up to the light and look for a crack.

If it is indeed the cavities being cut to large. RCBS needs to have that mold back.

I think it's only the cowboy CM molds that are registerd to 1-20 alloy.

[Pat I.]

What size are the bullets dropping out of the mould? The shank size should be .341 max. I've never had a problem with a RCBS and if you find the shank diameter is too large I'm sure they'll make it right by you.

I can't see them cutting a .357 mould to use 20 to 1 except for the CM moulds like was said

[Irascible]

Just reading the alloy literature which came with the mould. The shanks of the Lyman #2 cast bullets are .351". The driving bands are .360" I think I'll email their customer service. Even if the alloy is not what is spec'd it would not be that much oversize.