HI new to 10 mm just bought some RMR hardcore match RNFP .401 dia having hard time trying to reload any suggestion the cases go over size and will not chamber do the .401 need to be resized to.400.
Tnredneck ???
tnredneck, welcome to the forum! You shouldn't be having any issues but lets look at the things that might happen...
What firearm/chamber are you loading for? Is the chamber super tight?
Do you have a cartridge case gauge!
Where is it hanging up near the bullet? or near the extraction ring? Pass through Sizing if near the base or extraction ring.
Are you seating to depth without any crimp being applied? Some dies start to squeeze the case walls inward and that can snag the bullet.
Are you over crimping to cause a bulge? You need a light crimp to squeeze the casing walls straight with maybe the very slightest taper on the very edge. 0.4215" - 0.4220" is plenty.
What are you trying to chamber them in, and what is the actual measured bullet diameter? What is your finished crimp diameter? What is the COL? If they are in fact .401, maybe look at another suspect. I have no problem chambering .401-.402 in the tightest chambers. .403 are tight, but still chamber well. Perhaps you aren't seating them deep enough to clear the driving band (cylindrical bearing surface) - throat clearance. Resizing them won't likely cure it, if it's throat interference, as resizing them also lengthens the driving band. Also, most plated bullets don't take well to resizing, and I haven't tried it with RMR bullets. X-treme resize very reliably. Berry's regular pistol bullets do not, but their "magnum" rated bullets do (I routinely resize their .41M bullets to .401 for .38-40 Magnum use).
Try this:
Gently drop a bullet into the chamber and measure the bullet base to barrel hood. Measure the depth of a seated bullet, and subtract that from case length. If the numbers cross over, the issue is throat interference with a long driving band. If it is, seat them to proper depth, or choose another bullet design. Just resizing the bullet will result in unpredictable pressure peaks and reliability issues.
Another common problem is trying seat and crimp in one step. This can result in lead shaving up and causing issues. Pictures of loaded rounds and caliper measurements will help a great deal.
First I would like to thank the members who responded to my inquire about reloading RMR hardcore match RNFP.While I was looking going thru some of the threads on this web sight brass was in one of them so I changed to Starlight I was no longer getting spring back. What was happing the only way to get them to fit gage was over crimp that of course deformed the bullet. I would like to say a little about my self I turned 73 on the 12 of Sept. this year. I have been retired for 15 years from GM as a tool & die maker thank you all again.