Here is some data I have on my 22-6.5x55AI....
28" 12 twist barrel with 69 grain Sierras.
No problem stabilizing the bullet in the 12 twist (1000' elevation, 45 degrees and high pressure weather) since the bullet was cruising along at 3965 fps!
Used a load of 51.7 grains Alliant 4000mr to get this fps, made for a nice small group of about .4" at 100 yrds, I was just getting settled in as the last two shots went threw the same hole, only had 10 rounds of these 69 grain pills loaded up.
I like the 4000mr powder in this cartridge so far, it has a burn rate close to RL-19 from what I can tell, yet smaller kernels.
With lighter 52 grain and 60 grain bullets I tried RL-22 but felt the larger kernels created high pressure problems. Also tried H-414 but it seemed a bit fast with a pretty sharp kick. I did get impressive FPS but when things got really fast accuracy seemed to suffer.
Here are some impressive FPS I have gotten so far, keep in mind usual precautions and that I got this 28" 12 twist barrel Nitride processed which might account for a couple extra 100 fps. These are still probably over pressured a bit and for utmost accuracy with these 52-60 grain bullets they seemed to shoot better at 100-200fps slower then top speeds I have listed here. I'm not going for all out speed here, much more interested in accuracy but with a case like this....... You don't buy a Ferrari do drive slow
52 grain SMK @ 4300fps with H414
60 grain Nosler BT @ 4175 with 4000mr
60 grain Nosler BT @4130 with RL-22
69 grain SMK @ 3965 with 4000mr
I know I smoked a couple of the 60 grain Noslers with the RL-22 and didn't go any further. I think there might be some more potential with the 69 grain pills and 4000mr powder as I have only tried two loads and 10 rounds so far but was very impressed with accuracy, best so far!
Next I have some Nosler custom comp 80 grain bullets to try. I want to try some Ramshot Magnum powder with these or possibly even a heavier bullet. Do have a 9 twist to try these in as well if the 12 can't handle it.
Also reinforced the data that pressure is increased by quite a bit in a clean barrel with bit of gun oil in the barrel and chamber as my first couple rounds showed a good bit of pressure (ejector mark) but the last four rounds (even at 1.7 additional grains of powder) didn't show as much pressure (no ejector marks).
Think I'm only at about 100 rounds down the tube and certainly like the look of the 69 grain SMK load with 4000mr powder @ 3965fps!