We have a primitive weapon season in Mississippi which used to be muzzleloader only but something like 15 years ago this handi rifle became legal to use. Everyone and their moma rushed out and bought these handi rifles in 45/70 and 444. I actually have 2 45/70 and one in 444 marlin and sometime in near future I want to start loading for them but loading straight wall will be new to me. Last time I looked into it i do remember something about the length of brass in these handi rifles something like brass has be trimmed shorter than spec? I’m not sure but an internet search I’m sure will tell you something about that. Everyone I know and myself shoot Hornady lever revolution ammo. It’s definitely good ammo for the handi rifles with great performance on deer. It’s been hard to find plus it’s expensive. In 444 marlin the 265 grain has worked very well for us. No complaints on deer. Hornady sells these for reloading and I’m pretty sure that’s the bullet I would start with but I hadn’t looked around to hard yet to see what’s available in 444.