Rg1 has made the important point. H335 is a canister grade powder whose burn rate is kept within 3% of average by blending fast or slow held back lots into a new bulk lot as needed. That's how they keep load manual data valid for the powder. WC844, though. is the raw bulk lot. It's not at all unusual to see 10% or up to 20% difference in burn rate from bulk powders like that. If you tear down much military ammunition you see quite a variety of charge weights in different lots because of this, but they have pressure guns to test with and don't rely on recipes as handloaders do. So unless the vendor has done testing to show the H335 data really applies to this lot, you need to start with about 70% case fill under the bullet and work up while watching for pressure signs. Keep in mind that in the worst case the WC844 was surplused out because the military couldn't meet desired velocities and pressure profiles with it simultaneously.
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