[Timothy]

I’m about to load for a 10mm Witness. I will be using 155 gr. LSWC, 16 Brinell and will load on the light side for awhile till I get comfortable and things get broken-in a little. Would you recommend .400 or .401? Since I buy in 500 count I want to go with the best case scenario first.

Thanks in advance

[Quantrill]

The "Rule of Thumb" is .001 over groove dia. for lead. Quantrill

[Jeeper]

I seriously doubt that the mesurements are within .001 anyway but i agree to go with th 401

[braindead0]

The only way to be sure is to slug your particular barrel. You can get slugging kits from a variety of sources, or simply use a soft lead fishing weight or something close to size, perhaps some .44 caliber blackpowder balls.