Here's a group I shot this morning using the same bullet for 43 Dutch Beaumont you have - the 345 grain Lee sized .457. I used 27.0 grains of Accurate Arms 5744 and standard large rifle primers.
I shot this at 50 meters only using my shooting bag for a rest. I forgot the chronograph, but I estimate velocity in the 1300 feet per second range.
I fired two other groups which were very much like this one so I believe I will try for 100 meter groups next time.
The two shots in one hole do not show up as well on the target as they did on the meat-wrapping paper I use to record groups that are off the target. they are there, though!
Other than that, I tried for groups from my new Swiss Vetterli but have nothing worth reporting that way. About all I did was burn up my 777 loads.
SW
Very tight!!!