I know H4350 is the go to powder for the .260 Remington. I have been playing around all summer and early fall with RL-17 and though it took some work, I love it.
I am not seeing a problem with speed variations during temperature changes and am getting as good of accuracy as with the H4350 with much more speed.
I have found the KEY to RL-17 is seating depth. This has proven true on two different rifles. Once I started thinking outside the box and trying some extreme seating depths the RL-17 came to life.
Like many others, I was getting frustrated with speed variations and average accuracy. Then I started seating the bullets deeper and deeper. This morning I bug holded 5 shots at 100 yards with two different guns. One had a .120" jump, the other a .150" jump.
RL-17 likes a hot load in my experience as well. Be careful working loads because it will get you excessive pressure before you come close to 100% case fill (seating anywhere near the lands).
The .120" jump was a Berger VLD 130gr hunting bullet, believe it or not. The .150" was with the new Accubond Long Range 129gr. Both loads give me about 3060 fps and incredible accuracy with no pressure signs.
The load:
Remington 700 CDL SF LTD Edition
1:9 Twist
24" factory barrel
45.4gr RL-17 (This is beyond max load, do not start here and work up carefully. My barrel is treated with hBN as are the bullets and the barrel fire-lapped.)
CCI BR2 Primers
.260 Lapua Brass
I full length size each case with minimal bump of .001". I don't ream primer pockets or flash holes. I also don't turn necks, I just sort for neck uniformity and thickness. I use a Forster die custom honed to a .293 neck which has worked fine. It won't work with any other brass, though. Won't even hold the bullet with Remington brass. I have several bushings and a Redding Type S die for odd ball cases I use for plinking etc.
This is a factory rifle shooting well below sub MOA at 100 Yards with both loads and they both fit in the Remington standard magazine! Just barely, though. OAL is just under 2.90", so I have to be very careful to not damage tips if I load the rifle magazine.
So if RL-17 is driving you crazy in your .260, try seating the bullets much deeper into the case. I couldn't get RL-17 to shoot anywhere near the lands either. Even with Berger bullets, jam them babies into the case a ways and I think you'll be surprised. I have my Bergers almost to where the front of the bearing surface is at the top of the neck and they drive nails.
By the way, I've also shot these guns from 90° down to 35° and have seen little if any difference in speed, ED or SD, which all fall close to as good as I get with the Hodgdon Extreme Powders.
