H 4350 and 3300'/sec. But that is in a 6 Long Dasher. Slightly smaller case, but seems more efficient. 41 grns powder, bullet jammed .020, cci small rifle magnum primer............1 grn under maximum
in my gun. 26" barrel.
I have only tested for max charge/velocity, I don't know anything about accuracy in this gun yet.
Currently fireforming brass with 39 grns of said powder and same bullet/primer.
, you should be ok starting with 39 grns of this powder in the .243 because of the larger capacity. But do so at own risk. On the powder can it shows 40 grns of 4350 with a 100 grn bullet to be max in the 243.