?'s on proper slug size?

[Gun Nut]

I want to make sure i am doing this right. When i slugged my .40 s&w it measured .396 on the lands and .400 in groves of barrel. Wich measurement do I use? And then add .001 for final boolit size ..right? If i am thinking right i need .401

[fryboy]

barrels will vary with what they like best and often that depends with alloy and load , usually .001-.002 over is correct ( .402 dies seem to be rare in this caliber tho ) sometimes a barrel will actually shoot best with a groove sized boolit but from my personal experience ( and alot of reading here ) that's not the norm , often one will see in the lyman book where they did size to the small size , so yes .401

[mooman76]

Like fryboy said. .001-.002 over. Use groove size(the biggest).