Catfish, You are correct that WC872 (by itself) is not suitable for 308, because it burns too
slowly. I don't know if you noticed in the previous posts, but this thread is about using Duplex loads: more than one powder in the same load. Hence the obligatory warning in bold.
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The theory and proven practice involves, for example, two powders, one main charge and a smaller igniter charge (at the primer). Then full case capacity is used to minimize mixing. This has made these very slow powders useful for cast bullet shooters http://www.castpics.net/default.html
who have published certain data there.
I am performing some experiments based on published practice to try to identify other useful uses for this very slow, very cool burning, and very inexpensive powder. Specifically, I have tested duplex loads in 308 and 223. I have not found a perfect load yet for either, so far a heavy igniter of WC844 under WC872 in 223 with 75 grn bullets has worked best by far.