IMR-4064 Old vs New ?

[Pathfinder]

I read that the old H-4831 surplus does not have the same burn rate as the new powder which not surplus. Is it the same case for IMR-4064....often just refered to as 4064 in the old books .

The old Tried and true 130 grain .270 winchester load was 49.5 of 4064 before 4831 was available.

I now see that the max load of the same powder and bullet weight published by hodgdon is 47.5......Just modern lawyer proof load data or is the new 4064 faster burning ?

 

[bearhunter]

burn rates of powder, will change from lot to lot. Even though the container states it is a certain powder, which it most probably is, the burn rates can and usually will be slightly different from lot to lot and especially if its been jobbed out to a different manufacturer. The difference won't be enough to cause any safety issues, usually, unless you're at the extreme high end of the table.
It's the coating on the kernels of powder that govern the burning rates of powders. This is extremely difficult to regulate to exact thicknesses every time. They are very good at keeping the burn rates in spec though so nothing to worry about.

I like to buy powder in 8lb kegs for this reason. I know that once I've developed a load with this lot, that I won't be in for any surprises until it's gone.