Check the bore!!!!!!!
This is my first post and I joined to pass this information. Where I don't have the Handi itself, I do have the H&R (NEF) 45/70 Buffalo Classic. Even though I would imagine my rifle is a bit heavier than yours, it was a brute for kick with some factory ammo. I added the lace on "Kick Killer" butpad and filled a 3/4" copper pipe with lead to install in the stock bolt access hole. That sent the kick off to a new home. lol The pull is now a tad long ,but still a joy to shoot. I do reload and am having problems with leading in the bore with 300 gr. hard cast lead. It shoots jacketd bullets like a dream. I should have known enough to check the rifling closer but just didn't just cleaned it and started playing. I have tried IMR 3031 amd AA 5744 in low vel. loads but is still leading from the Suters Choice 300 gr. bullets. I'm not giving up by any means, and will send in for re-barrel if need be. Other than these cautions, I think you will really enjoy that rifle. There is a video on You Tube of a fella loading 45/70 sitting on a tree stump with the cheap Lee Classic Loader. The full set of powder dippers is something on the order of $10-$12. I have a fairly new Hornady single station but am still going to order the portable little kit. I am quite intregued with the Handi rifle platform and plan to get some, as I enjoy single shooting. Sure hope this rambling info helps some . ole shooter.