204Ruger

I am working up loads for a Cooper Model 21 and have been seating bullets .020 off of lands. What have
shooters found that works best for them. Thanks in advance.

With which bullet? I use the 26 grain Barnes Varmint Grenade in a 1:12" twist and Nosler's 32 grain BT lead Free in a 1:8.5" twist, also the 50 grain Berger HPBT. The 26 grain Barnes and 32 grain Nosler both seated to 2.260" or the Berger seated to 2.300" shoot .250" - .300" groups (10 shots). Seating close to the lands is nearly impossible in some chambers, and my experience is that the lead free bullets like a bit of clearance. Although my barrels are customs made by Shilen or Pac-Nor, so may not be chambered similar to Cooper.

Shooting 32 grain BK seated to oal of 2.341 getting .375 groups. Lands measure 2.394 and figured moving bullet closer to lands should tighten group but did opposite which surprised me. I developed this load for my CZ and figured I could tweek seating depth of bullet to get even tighter groups out of Cooper. I will leave owl length static and start playing with powder charge.

vanhammer: As you most likely know, each rifle is a rule unto itself, especially in regard to load and seating depth. That said, out of five .20 caliber rifles I own, one likes bullets seated .002" - .010" off, or at the lands, depending on the bullet, one likes .040", one .080" and the other two (204's) both run tight groups at .090" off the lands, typical for a 204.

Here's a group shot with my 11 twist 204 and 40gr V-Max. If I back off the seating depth to "factory" spec's, the 'group' looks more like a shotgun pattern than a rifle-shot group:



There's just no set rule to this, you just have to experiment with both seating depth and powder charge to arrive at the best your rifle will do. Good luck with the quest.