Re: OK So the .260 Rem teach me
My rifle now employs a single feed follower, so mag loading is not an option for me.
That said, I'm pretty sure Black Hills, etc., produce their 139gr Scenar loads at magazine length, and many reports say they work well.
For mag length rounds, I believe an HPBT bullet profile probably allows less seating depth than a bullet with a ballistic tip, and I can say with confidence that the 142SMK works very well in this chambering.
I have never seen any evidence of a donut or a problem that could be attributed to a donut. Part of this may be a consequence of my personal technique of only resizing the very end portion of the case neck. The load 43.8gr H-4350, 140A-Max/142SMK, does not appear to require shoulder bumps, which would be my guess regarding where donuts originate.
These days the Dancer is doing a time-out. When Bodines was withdrawn from HP/F-Class comp, I lost my LR site, and shooting the .260 at distances I now have available (250yd max) seems somewhat of a waste. Much of that shooting is being done with .222 and .223, and I'm looking into a shorter barreled .30BR.
Greg