Took the Marlin 1895 GBL out today to get ready for deer season. I've been trying to get a load worked up for the accurate 460-405V bullets Waco was nice enough to send me.
Think I've finally settled on 44gr of IMR 3031 lit off by a federal primer.
One of Mikes lubes I picked up on the other forum. Think he called it Satans lube cause the formula is 6 parts Vaseline, 6 parts paraffin wax, 6 parts beeswax, and 1 part ivory soap.
Honestly is pushes you some but is not brutal. I tried shooting some 350gr ranch dogs about 1600-1700fps and the recoil was much sharper.
These slow 405gr bullets just shove you around. I also added a limb saver recoil pad which helped a lot.
3031 is my usual go-to powder for 45-70. If you start getting close to 50 grains with a 405 grn. bullet, you better have the butt plate pulled up real tight to your shoulder or your going to grimace after the hammer falls.
Easy shooting load for me is 22-24 gr of 2400 with a 405-420 gr cast bullet. 24 gr gives me 1400 with a 420gr plain base and it shoots awesome in my Marlin. Easy to shoot 50 in a day with no pain.
I tried your recommendation of 42 gr. My rifle strung it vertically about 5". Couple more grains calmed it down. I probably need to go up a couple more but I don't want recoil to get brutal.
I am currently shooting Lee 405 HB in front of 38.5 grns of IMR 3031 in my 1895. It likes it and so does my rebuilt shoulder! Chrono's at 1325 fps. Flips a small Southern whitetail end over end at 85 yds and no meat damage. Looking to go up to 40 grns, and might work up a grain or two more based on your load. But it is a very easy forgiving load on the shooter and very terminal on the receiving end!