22" mate, but I think I have a fast barrel as Charlts on here couldn't crack 4000 fps with accuracy from his 243.
I don't think the powder needs to be H4895 specifically, just look for a powder that gives maximum velocity with around 40-45 grains of powder. I noticed this issue when developing a load with 55 grain ballistic tips for a friend of Adamant's with RL 17, another slow powder for this use, and using 49 grains of powder for around 3800fps. Hell of a muzzle flash but that may have been just due to the design of the Hardy moderator he used, by all means try your load under NV before changing.
I plan on using N140 after my stock of 4895 runs out but from my experiments will lose around 150-200 fps velocity, not that this makes much difference in this case as we are talking about around 5%.
Load data for your bullet here:
http://www.hodgdonreloading.com/data/rifle
Max load is 43, bear in mind I am one grain over max in my rifle with 45.5 using a slightly lighter bullet, keeping a close eye on the chronograph and with what I call my "pressure shakedown test" which is loading a single case with the same load over and over again on the firing line until I see loose primer pockets. With Geco brass I tested this load ten times with a minimum batch capacity case and found no evidence of primer pocket loosening over that ten and so I think it's safe in my rifle, it may not be in yours.
What other powders do you have?