Sven - would you be so kind as to measure the rifling twist?

Would this rifle be capable of handing any Lever Action-Marlin-type load?

That would be in the relm of 43,000psi.

Depending on the twist, I might have some loads with heavier than normal bullet weights, ie: 340gr. to 400gr. from an article many years ago in Gun Digest - might have been by Frank De Has. I'm quite certain I still have that publication if you are interested. Much depends on the actual rate of twist - and what it is regulated for.