Winchester to Lapua brass?

[guncrazy72]

Hey everyone, I know this question has been asked many times before but I can never seem to find really what I am looking for in those post. Ive duplicated the FGMM 175gr load using:

FGMM brass trimmed to 2.005
IMR 4064 at 42gr
Federal 210 primers
175 SMKs
OAL of 2.800

This works great out of my rifle but I do not have that much of the FGMM brass. I was able to buy some once fired Lapua 308 brass yesterday and need to know how much I should change the powder charge with the Lapua brass. From reading Dan Newberrys thread on FGMM it looks like they use 41.7gr of 4064 with a minimum charge of 41.5gr of 4064. Should I leave it at the 42gr or drop it down some and see? I am on the very low side of this powder charge since the max load is 45.6gr of 4064.

 

[CharlieNC]

Size the Lapua brass to fit your chamber, then check the water capacity for comparison. If the Lapua is lower then you may want to back off powder and re-do your load development, working up to a node.

 

[varmint slayer]

I'll bet money the Lapua cases will need less powder to get you the same speed.

 

[M40_A1]

From reading Dan Newberrys thread on FGMM it looks like they use 41.7gr of 4064 with a minimum charge of 41.5gr of 4064. Should I leave it at the 42gr or drop it down some and see?

Every lot of powder will need to be tested. When switching lots I always run a velocity comparison between factory FGMM and a few different loadings to find which one matches the factory velocity at that same range session. That is one reason why you will see different loadings from different people at diferent times. THERE IS NO ONE CHARGE WEIGHT FOR A DUPLICATE LOAD. Even charges from different lots of factory FGMM will vary for this same reason. One lot of 4064 needed 41.2 grains to match, and another lot needed 41.7 grains. You'll have to check for yourself with your lot of powder.

Now, when I switched from Federal brass to Lapua I got the same velocities with the same charge when using the same lot of powder.