Do I need new dies for 10mm?

Don't know about RCBS dies, but my Hornady set shows as being for 10mm/.40S&W, so I'd assume you could load both with those too.

What I'm saying is that if one companies marks them that way you can likely use another companies even if they aren't marked as such .

They're both the same caliber and both straight wall. The FL-size die will size both properly. The flare die when adjusted correctly will flare both as needed. Same with the seater die.

All you'll need is plenty of extra powder.

You can use 40 to do 10mm, but not necessarily the reverse. My Lee 10mm dies are too long for a 40 case to fully enter the expander. 40 dies can simply be adjusted upward to accommodate the longer case.

The .40 RCBS dies are for both 10mm and .40 S&W. I use mine for both all the time.

It's the same as with .38/.357 dies. You can buy a spacer of the proper thickness and you won't have to change your die settings at all. You just unscrew the die that's set up for .40 S&W, place the spacer under the lock ring, and screw it back in and start reloading.

I bought a bunch of spacers of different thicknesses at an industrial fastener store, and I use them all the time. They were cheap, too.

You'll need a spacer .142" thick.

Hope this helps.

Fred

They should work same bullet dia.

...but you will need large pistol primers.

Why wouldn't you just shoot off a quick email to RCBS? I think they would know.

In case there are any questions.

I was reloading 10mm before there was a .40 Short & Wimpy... I had to buy a seating/crimp die for the forty, but the other dies are usable for the forty. The .40 dies are fully usable for the 10.