I reload 4 cartridges: .22-250 Rem, .257 Wby Mag, .270 Win, & .308 Win. For the .22-250 and .308, most any load I try from the manuals shoots well. Granted, some shoot better than others, but they've all been reasonably accurate off the bench at 100 yards. The .257 and .270 seem more finicky about what they're fed, with some loads yielding 3" groups and larger.
Is it the cartridge, or the rifle? Are some cartridges inherently accurate and easy to load for? Are shorter cartridges more accurate than long ones? I've noticed target rounds, such as the PPC and BR cartridges are short, fat cases. Are Winchester and Remington on to something with the the short and super short magnums? Or is it just the gun? (or for that matter, the scope).
All guns are modern, sporting rifles with just one owner.