Powders for .308?

[Unclenick]

Originally Posted by jmr40

… I … preferred Varget or RL-15. Here is why. Those 2 are the least sensitive to extreme temperature swings.

My understanding is the reason Federal dropped RL-15 (current 168 grain SMK powder in GMM .308 and M118 LR powder) for the Mk.316 m.0 sniper load they worked up is there were pressure spike problems observed with it in desert temperatures in the M118 LR. Their solution was to go IMR 4064 for Mk. 316.

IMR 4064 seems fairly remarkable for its age. John Feamster did a test that's in the 1995 Precision Shooting Reloading Guide in which he loaded IMR 4895 and IMR 4064 to the same mean velocities under 180 grain bullets. At 2200 fps it took less 4064 than 4895, by weight. At 2400 fps the charge weights were about the same (within 0.1 grain, IIRC). But at 2500 fps it took more 4064 than 4895. The two powders have pretty similar chemistry. The difference is in the grain shape. The 4064 just did not increase burn rate with temperature and pressure as much as the 4895 did. This means it is less sensitive to pressure changing influences in general.

Varget is intended to compete with 4064 on the burn rate charts and be even less temperature sensitive. It works well, but I've never been able to get quite as much out of it in terms of velocity for long range, which likely explains why Federal didn't go with Varget for Mk. 316.

In the meanwhile, the Valleyfield plant in Canada that make the IMR powders has changed their process, declaring the original to be too expensive. I don't know how the newer process 4064 compares with the other. If they got it right, they'll behave the same. If not, everything I just said about 4064 may go out the window. I'm still on an old supply of 4064, so I just don't know.

[TMD]

Varget has always gotten me the best groups in both my .308s with 165gn noslers

[TheNatureBoy]

4064
RL-15
3031
Varget
4895