Forget the marlin rifles there a crap shoot if you buy one. Bad quality all the way around. Buy the browning BLR in 450marlin. I'm shooting 7/8" groups at 100yrds using reloader 7 and the hornady 300grn HP bullet. Its just a better gun. If you reload you will have all kinds of options from pointed bullets to round noses.
IMHO
Been shooting Marlin 45-70's for 25 odd years and never seen a problem with any of them. Mind you I'm shooting older rifles and not the new ones. I would buy another Marlin today if priced right. In my book it's one of the best rifles ever built.
No disrespect to you in my thoughts but there are good and bad rifles built and anyone can get a lemon. But I've never seen one.
In regards to the 450 Marlin round it's a great round. But if you don't reload it's tough to find ammo.