I highly recommend measuring how far the bullet has to jump before it touches the lands in the throat. In my Marlin 336.
the bullet has to jump 0.2" before it touches the lands at cartridge maximum OAL. That is, if the cartridge length is a less than or equal to 2.550" I can eject a loaded round. If the the cartridge OAL is 2.60" or more, I have to remove the lever screw, remove the lever and bolt, and then with medical forceps, I can remove the round from the loading port. And for my bullets to be set out long enough to reach the throat, the cartridge OAL has to be 2.750" . So, just from measuring bullet jump, you can understand just what limitations you can expect in terms of accuracy. Generally, when a bullet jumps two tenths of an inch before it touches the rifling, you will never, ever, develop a load that shoots sub MOA, or even MOA. As you can see from my targets, my Marlin will with its best loads, shoot somewhere between 2 and 3 MOA out to 200 yards, with 3 MOA being pretty good for this rifle.
My rifle really liked N135. My loads are way above any manual maximum, but that is primarily due to the chamber being cut with something more resembling a Polish sausage than a reamer. My chamber is as huge as the throat is deep. I talked to Marlin just at the turn of the century, and Customer Service explicitly told me they built their rifles for the guys who shoot at most, 50 to 75 yards. That was their customer, and their customer was no marksman and their customer seldom, if ever cleaned their rifles. So understanding who their customer is, it made sense to ream huge chambers that rats could build nests inside of, the mechanism could be rusty, and yet the rifle could still eject a fired round.
I tried to develop loads that pushed a 170 grain bullet 2150 fps. This rifle is extremely sensitive to velocity extreme spreads. Powders, such as N135, which give tight velocity extreme spreads, gave the best accuracy. Also, in my Marlin, the rifle shot the best within a very limited velocity range. The closer I got to factory velocities, the rounder and smaller the groups. A 150 grain bullet is about a 2250 fps affair.
IMR 3031 was a good choice
I bumped the load up a half grain because I was still below my goal of 2150 fps, and took the rifle to CMP Talladega. I don't know what the exact velocity is, but it shot well enough to be a viable hunting load at 200 yards.
Accurate Arms 4064 shot surprisingly well. But notice the huge elevation changes a grain of powder makes in the point of impact. I am of the opinion that lever actions are about as rigid as a trampoline, and therefore the dynamics of the rifle are extremely sensitive to the energy input of the cartridge.
Kept on bumping up the charge, don't have the velocity for this either, but it shot well at 200 yards
I am going to recommend IMR 3031 for this cartridge. I used up all of my 1960's IMR 3031 and never wanted to buy any again for the stuff was long grained and threw poorly in my Dillion 550B. But, IMR has changed IMR 3031 and it is a short cut powder. IMR 3031 is a pre WW2 powder and shoots well in the 308 Win and is an accurate load in the 30-06 and the 223. It is not a velocity champ in the larger cases, but it shoots well. I have found references to IMR 3031 being a factory powder in the 30-30 prior to WW2, so it has a good track record.
I went with 170 grain bullets because this is such a short range weapon, that any added velocity you get with 150 grain bullets, barely affects the trajectory (within hunting distances) and I believe a 170 grain bullet will make a deeper wound channel, all things being equal.
Vihtavuori was my best performing powder, but the stuff is too expensive and the shelf life is only 20 years. There are lots of posts where 20 year old Vihtavuori powder went bad.
