I agree, if you set the dies up to load factory spec. ammo, you won't have any problems firing them in his rifle, then, while he's there, you can back the die off until you're not over-resizing the once-fired brass and also set the bullet out a little to match his chamber, if necessary. New brass, you always want to full-length resize the first time because it exceeds maximum specs. You'll probably want to check the overall case length after you size them and trim them back so they're all equal. New brass will vary in length after the initial sizing, since that's where the excess brass is "squeezed" to. Check the primer pocets/flash hole for residue after trimming, sometimes you get chips in there when trimming. Hope this helps, it's how I always proceed.
