I bought a large quantity of Sierra 225 grain Pro Hunter bullets (non catologed Sierra item made for Federal) because this rifle likes the 225 grain Federal Classic factory load. My intent was to duplicate and possibly better the factory load with my loads. I ran into an interesting anomoly though finding that 70.5 grains of IMR-4350 produced higher velocities than 71 grains? Although this was only a 5 shot average I thought this was interesting for sure.
Rifle is a Win M70 Classic Supergrade .338 Win Mag with a Leupold 3-9x50 Vari-X II.
Best load was 70.5 grains of IMR-4350, WW cases new and un-fired, CCI mag primers, Sierra 225 grain Pro Hunter bullets, average velocity for 5 shot string was 2815 fps. Windy day, 75 degrees, 6,800 ft. elevation. Distance 100 yards.
The taped over shots were shot on a previous day with a 9.3 and not part of this group.
Best group was .49" center to center, next group was 1.03"

quote:

Originally posted by Snellstrom:
I ran into an interesting anomoly though finding that 70.5 grains of IMR-4350 produced higher velocities than 71 grains? Although this was only a 5 shot average I thought this was interesting for sure.

Most single base powders demonstrate this phenomena. When incremental loads are chronographed, it is common to see gains of around 100f/s per grain of powder. At some point (nearing maximum pressures) the increases in velocity become less linear -and you've just witnessed it. This is exactly why one shouldn't start with book maximums. I look for this on the chronograph and often push loads a grain or so more just to verify that maximum pressures have in fact been reached. More often than not, the best performing loads come in 2 to 3 grains below the true maximum pressure. IMR 4350 really is a miracle powder, isn't it?

Yes I think you are right on the money Buckshot.
I find that if I am using IMR-4350 and find an accurate load low in that cartridges velocity potential that I can push ahead a couple grains and find that accurate "spot" again. The accuracy seems to be a rollercoaster as you move up in velocity.

That looks VERY familiar!

The load for my 338WM for many years was 70.5gr of IMR4350 with either a 225gr Hornady SP or Nosler Partion. Same MV(2820fps), same POI with either bullet.

I've since tried RL19 and get a bit more MV but the same accuracy. I use RL19 in my sons 243 and 6mm. With the cost of components going up, I wanted to combine components then buy in bulk.

RH

This has been my favorite load since 1983.