No, there really isn't a specific regimen, based on the number of rounds. It SHOULD be based on the amount of fouling. Some barrels are just slicker than others, and foul less. Most slick up some with use.
If you want to think barrel break-in, the more cleaning, in the beginning, the better - up to a point. You will probably find that, as the bore slicks up from being fired and cleaned regularly, the needed cleaning interval will get longer. Just be sure you're really cleaning it - copper and powder fouling.
Just clean as is convenient, and don't worry about it. What else ya' gonna do? BTW, be sure & use a guide/muzzle guard, so ya don't get any crown wear, when cleaning from the muzzle. JMHO.

The 45/70 I've wrestled with to get back on track with accuracy is doing OK,exept I notice minor copper streaking at the bore in about 12 rounds.This doesnt effect accuracy,and I think it foolish to have to clean so often.Is it a matter of going to the range and blasting until it doesnt hold accuracy anymore,or do you guys have any ideas as to how many rounds.I know every guns different,but perhaps somebody has been through this with a modern marlin.Thanks

I clean every firearm I take to the range, even if it doesn't get fired. Firearms that haven't been fired in over 3 months get pulled out of the vault and cleaned.

Thanks Puncher,but if I clean this thing every time I see streaking at the muzzle(12 rounds)that makes a hunting trip away almost impossible.So apart from a time line,there must be a # of rounds line.

Thanks Bug!!!!!.I think I sweat this stuff a tad to much

Charger--my marlin does the same as yours but accuracy doesn't fall off for me either so I don't worry about it. If you really want an eye opener try the barnes x-bullets for the 45-70.
They shoot really fantastic but about 2 shots down the barrel and it looks like a pumpkin. AND...man oh man with that big bore you really do notice it. Not just small streaks either. Those bullets shoot really good and I can't imagine a tougher bullet. Takes a couple of applications of "wipeout" but can get it clean ez. I'm a big believer of taking a "fouled" gun hunting--not a clean one. I don't have a boresnake for the big 45-70 but do have a 30 cal boresnake and have found it to be wonderfull for getting lot's of shots out of any of my 30 cal guns when developing loads. (Pass it through about every 10-15 shots or when changing recipies) Maybe one of these would work for you. 2 passes of a boresnake before using "wipeout" seems to also speed up cleaning.