Lyman and RCBS sizer interchangeability

For many years, I had only one boolit sizer, RCBS. My assortment of H&I dies is a mix of Lyman and RCBS. Either brand of die fits into my RCBS sizer, completely interchangeable, or so it seemed.

Recently, I bought two Lyman 450 sizer machines, one from a local estate sale and another from eBay. Both were fixed up with some fresh parts and put into service with White Label lubes. I now have the RCBS and one of the Lymans set up with BAC lube for rifles and the other Lyman with 50/50 for pistols.

Only to find out that while Lyman dies will fit nicely into the RCBS sizer, the reverse is not true. Lyman dies and the hole they fit into inside the sizer are about .004" smaller than RCBS dies and sizers. Reminds of the Russians and their 82mm mortars, they can use our 81mm rounds but we can't use theirs.

All of this is probably well known to the old hands here, but I'm now learning it the hard way. Just wanted to commiserate. - CW

Wow! Chas;
That's a new one on me.
I've had both machines and a mix of dies for decades and NEVER found incompatability. Guess I;m just a lucky duck EH?
I'll have to be more cautious on further purchases.
Thanks.
Pepe Ray

Strange, I got a RCBS 0.452 die in my Lyman 450 right now, both mid 1980s vintage.

Same thing happened to me. I purchased a Lyman 4500 lube-sizer and a RCBS .356" die. The die would not fit in the sizer. I called Lyman for technical assistance...They said that RCBS and Lyman USED to be interchangable. Some time ago (not sure exactly when), RCBS changed the OD diameter of thier dies, and now can only be used in LAM's.

That sounds like something RCBS would do. It's a wonder that they didn't do it sooner.
Pepe Ray

I read this today, just has I was having problems sizing in an RCBS LAMII with shorter 45 boolits. Not the same issue, but the difference in holes in the dies. I forgot I had both dies, and had put in the Lyman. Lube ears flowing on every boolit. Thanks to reading this, I realized my error. Switched dies, and problem solved.

Doug

This situation may be just an instance of being off a couple of sigmas too far on the bell curve of tolerances, I've generally been able to interchange RCBS and Lyman/Ideal dies in all the machines, However, I have one Lyman die that is a tiny bit too long for the #45 machines; it now permanently resides in my Lachmiller lubrisizer, where it fits just fine.

I called RCBS about this some time ago, so it's not like they don't know. I had to chuck them up in the lathe and turn about .004 off of them.