Just depends on the throat and the ogive of the bullet, load up a dummy round and see how far out you can seat it and still close the action without marking the bullet, or just make a COL gauge as shown in the FAQs. H&R 45-70s are notoriously short throated, but not all of them are, I have 5, 3 of them wouldn't load 350gr-405gr jacketed bullets to recommended 2.55", one will, the other one got ultra throated to 45-120 before I ever shot it, so I dunno how deep it was!!
Tim