I have a CZ527 in 6.5 Grendel and a 18" Satern barrel on an AR platform.
Frankly the AR is more accurate than the bolt gun.
What the planned use will determine the choice.
Based on my experience with the 375 Bee, you should get higher velocities with RL-17, but H4350 is a solid performer too. With a 300 AB I can get almost 2700 fps in my rifle with H4350 and another 80 fps or so with RL-17.
46.0 gr. of Lever got the 250 NPAR slightly above 2300 fps at 15' from the muzzle and there might be another 50 fps available.
According to the ballistic tables the velocity of the 338 Federal with 250s differs from the 338 WM by ~ 200 yards. A 338 WM at 400 yards is about the same as a 338...
Mine wears a 24" barrel. With the high expansion ratio of the cartridge to bore volume, I don't that you will see a significant impact going from a 24" to a 22" barrel.
I totally understand your powder situation, but in some ways it's worse to be short projectiles.
In my rifles I have found that IMR 4451, RL-23, and IMR 7828 all perform well from both the accuracy and velocity perspective with 90-100 grain bullets. 7828 really surprised me with 100 grain...
I have a collection of M88s myself, and had one of the 308 rifles picked out to have JES rebore it to 358. Then magic happened as I was able to purchase a nice pre-64 358 at well below market price. The 308 rifle went into storage and I didn't think much of it until the 338 Federal was announced...
One has recently come into my possession and has made a couple range trips. No earth shattering results as yet, but the 210 NPAR is looking promising. It looks like Leverevolution is going to generate the highest velocities and Varget is in the lead for accuracy.
In the old days a big bore...
If you are truly looking for a long range rifle, visit a benchrest match and see who is building the winning rifles. That's what I did and the outcome was well worth the effort.
http://castboolits.gunloads.com/showthr ... ase-powder
7383 "triple base" story origin
I'll tell you exactly how the "triple base" story got started. Back in the late 1990s-early 2000s my friend Linstrum told me in private E-mails of the great results he was getting with basically full case...
I have a stash of these bullets and would like to try them in my 45/70 double rifle that has a MAP of 32k psi. The barrel length is 24", the COL would be 2.800", and the max loading density would be 102%. Much appreciated.
Have an ARs in 223, 224 Valkyrie, 6mm AR, 6.5 Grendel, 6.8SPC, 30 RAR, 7.62x39, 350 Legend, & 458 SOCOM. My 6.5G AR delivers better accuracy than my factory CZ527 bolt gun and runs flawlessly. I really wanted my 6.8SPC to perform with the Barnes 95 gr. TTSX pushed by AA2200, functioning is...
I have a couple rifles in 6mmAR(aka 6mm Grendel) and find the tweaking of the case design to create a "new" cartridge amusing. I think they just wanted to claim something as their own, rather than offer a tangible improvement. That said, it's a much better choice than the 6.8SPC for the AR...