I load a variety of loads for the Marlin Guide gun. Basically I have hunting loads and one plinking load. My plinking load is intended to mimic the trapdoor load and has no recoil and trajectory about like a 22 LR. I have a Lee mold that throws a 340 or so bullet. I then use Unique powder, 14.6 grains, you can find those loads listed in the cowboy
action section of reloading manuals. Mine averages 1,190 fps. It lets me practice without recoil, yet still is ample for any deer or hog out to 100 yards. I sight it for 75 yards, after that the trajectory is like a brick or foster type shotgun slug.
I do like the Hornady ammo and it gives the flattest trajectory you will find. They claim about 2,050 fps, in my shorter barrel it goes 1,809 fps which is pretty flat and a 325 grain bullet so plenty of thump.
I have loaded 300, 350 and 405 grain bullets and probably like the smaller ones better but no pet load. The books tell you to use 52-55 grains of most powders. I like to shoot and with components an issue these days, I like to use my cast play load. The cost of the bullet is just the cost of lead and electricity probably well under 10 cents, then a 4 center primer and that 14.6 grains of Unique costs only 7 cents, the cost being 20 cents or less per round, or $4 a box, vs $40 a box for any factory. I use Starline Brass and just for grins I suggest you at least try one bag of the nickel cases. They look awesome.
I have not yet hunted with it since I hunt the wide open spaces. But the 45-70 has lots of other uses. For example, if you have an unwanted tree or stump on your property, you can pretty well cut it off at the ground line with a box of ammo. Or if hunting hogs you can just line them up and take 2 with one shot, or so I have read.
Enjoy.
I have killed deer with my cast bullets at even less velocity out of 50 cal front loaders and look forward to it. You will enjoy the caliber and the Marlin. I collect levers so I am biased but with the big ammo, it is just special welcome to the club.