I may have found out why my .260 isn't shooting tight groups. I measured the concentricity of the necks once fired and then after laoding I measured the bullet run-out. What I am getting is the necks are out by .0025 and the bullet run-out is .005. I am using the RCBS Case
aster Gauging Tool. I am using the Redding Competetion Seating Die and a Redding Neck Sizing Die. The FL die is an RCBS. Is it the poor quality Remington Brass? How can I make the case and bullet more concentric? These are brand new dies. Should I return them? Will these variances make a big difference in accuracy? Could this be the result of poor groups? As stated before 1.25"@ 100 and 3.00" @ 200yds. Thanks for the help.

I'd be very happy with those groups if they came from an out-of-the-box factory sporter. On the other hand if it was a full blown benchrest gun then I'd be pissed. Are you saying factory loads yield smaller groups?

If you only see .0025 on your case necks you`re doing OK. There is most likely that much differance in neck wall thickness in your cases. I`d look elsewhere for your problem if you`re shooting a factory rifle. I don`t think you have excessive runout, more than you might like, but not excessive.

Onefunzr2:

I never tried factory loads in this gun.

Interesting comments on concentricity & sizing technique in thisBarsness article

I solved my runout problems with the Lee collet neck die. A great die and you don't even have to lube your cases.

It seems that your problem is not runout. I'd look at seating depth if your powder/bullet combo is relatively proven. Start with the cartridge OAL given in the Lyman book, or determine what seated in the rifling depth is and back off 5/1000. Ku-dude