Gunner, look at the thread...
... on the second page of the thread list in this forum:
"To carry on where we left off...Smokeless in a Mauser M1871 or 71/84
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... produces poor accuracy.
Reason: the fast pressure onset with smokeless bends the action body to one side like a banana, because of the single locking lug, and the "whip" is transferred up the barrel in addition to the longitudinal shock wave that is always generated in every system. When this whip reaches the muzzle, the resulting deviation produces lousy grouping.
Best performance in that long barrel with the single locking lug will be obtained with the slowest rifle black powder you can get - I use Swiss No. 4 i.e 1 1/2 Fg.
This opinion is not just my own experience, but the common conclusion of the BDMP competition shooters who use these rifles. As this is the 3rd time this year that the question came up on the old Jouster boards, I humbly submit it could be included as an FAQ.
Patrick"
That's enough quoting from myself. read the entire thread, get cases direct from Horneber or via Johannsen. Load with Swiss No. 4. Plenty of lube. Bullets you will have to cast (about 3 to5% tin-lead) and size to 0.446".
Patrick