Congrats on a very fine rifle. Possibly Mic can also address the feeding and full cycling of the standard length .45-90 cartridge so that you will not have to trim cases to make them cycle for you..
Please let us know.
BTW, couple weekends ago, Ricky, 86er, and I ran some of my initial mid speed reloads (good plinking loads) through my Japchester .45-90, shooting offhand at 50 yards. These were 325 gr cast Beartooth bullets over nearly 40 grains of 5744 and they shot well with no discernable recoil. Ricky put all his into the black in a nice small group, despite a gusty breeze.

That 9.5 pound rifle damps out a lot of side wind movement as well as recoil.
I also shot up some of 86er's extra 430 grain factory .45-70 loads

(they were either BB or Garrett, do not remember) and put my first two within one inch of each other before I got sloppy and had a flyer. These had a firm kick, but no problem for the hunter trying to put down something big and nasty. THey were similar to the 500 gr .45-90 sharps loads we had begun the day shooting. These are too long to cycle through, but can be loaded singly into an open action. Gotta shoot them though, as the tip will bind if you try to work the lever to eject them; awful problem, eh?
This kind of shooting is really fun and now that my 1892 .357 is working again, I plan to do more of it.