From my notes on different primers.

[Catfish]

I have desided on H-870 as my powder of choice for now in my .22-6mm. So today I started checking different primers. Since thr case is full of powder and no presure signs I loaded everything with the same powder charge. I tried 5 different primers, CCI BR-2. Win. LR, Win LR mag, Rem. 9 1/2, and Fed. LR Mag. Match. The biggest suprise of the day came when the WLR primers were 9 fps faster than the Win. mag primers. Actually there was only 9 fps difference in vel. and standard devation was the same, 27. The Rem. 9 1/2`s had a SD of 15 and grouped very good. The Federals came out on top with a SD of 10 and was the fastest loads, by 1 fps over the WLR primers. To tell the truth there was only 55 fps between the fastest and the slowest, and all groups were so close to 1/2 moa that you would be splitting hairs to say one was better, but I did and went with it.
So far I`ve put abt. 500 rounds down range working on the best load from the .22-6mm. I do know that mine doesn`t like any load much over 3,200 fps, and I can push them up to 3,600 fps safely. I may try shimming the barrel next to see if I can change the harmonics and get it to shoot better with faster loads.
I`ve been shooting 80 gn. Serria MK`s. The only other bullet I tried so far was the Hornady 70 HP`s but I`m pushing them way over their max, velosity and blowing them appart in mid air. May also try the Hornady A-Max. bullets, or the 80 Bergers.
I fired 1 group at 500 yrds. with this gun and put 3 shot into a 3 1/2 in. group. That was with some of the first loads and they were only moveing at 2,800 fps and I`m wanting to get back to the 500 yrd. range and ive the 3,200 fps. loads a try.