Hi, a keen owner and shooter of a Win 1885 (Miroku) .405 Win traditional hunter as well as a Ruger 1-H tropical in same.
So far done a lot of shooting with the Winchester and a tackdriver...even with Marbles tang sight. It normally takes about 3 shots to get some lube into barrel and then then settles down in that can call the shot as it goes off!
Have a custom Mountain Mould 330gr nominal GC bore rider (sized 0.413"), and average velocity at about 1910 fps.
The chamber is tight (minimum SAAMI spec) in that need the case mouth to be not more than 0.436 to chamber with a cast bullet. With FL RCBS dies, the case is hugely expanded by the length of the bullet into the case...
Have now spent some time with my Ruger, and find shoot's high until the barrel warms up, with side spread of about 1" and vertical 2" (at 100m) from cold to warm barrel.
What is very interesting is that the fired cases in the Ruger drop back in without any resistance and the case mouth is sitting at 0.438. This would suggest that the Ruger chamber is cut to max SAAMI spec of 0.4368 plus 0.002. The fired cases from the Ruger will not go fully into the 1885, in that the case are out of battery by about 0.160" when pushed in tight!
The sized 0.413" cast bullet will go into the Ruger fired case with a tight friction fit.
Going to do some tests with part sizing the cases (for Ruger) with a RCBS trim die and size to 0.437 OD at case mouth to engage with about 0.001 case tension to see if improves accuracy.
Going to do the same with partial trim die sizing on 1885 to see if can get to size by minimum amount to get a more even case "shape"
Brass is factory new Hornardy, once fired.