I tried out some 240 gr lswc loads I made up with Unique 10 gr. Thankfully they all cycled just fine, but the accuracy (at 50 yds, to sight in with the factory sights, for now) was awful. We're talking all over the target printed on a piece of standard copy paper.
I've read about slugging bores and sometimes the Marlin lever actions being a bit big. I usually order from Dardascast bullets. Would it be easier for me to order 100 rounds in each larger diameter size and just shoot them all to figure out what the gun likes?
Its funny, because I was shooting my 357 revolver the other day with some .357 sized (I ordered incorrectly) cast bullets, and they were shooting as well as the .358 I had.
Does my problem sound more gun related? This is a new "Remlin" Marlin made recently at the NY plant, so I've read all kinds of horror stories on the internet about the problems they have. Mine seemed like a good one, since the action is smoothing out and it fed the SWC shape no problem. Maybe just bad trigger and sights?
At least the load didn't lead the barrel. It's pretty funny looking into that giant bore and cleaning it out. No mysteries of what is in there, you can see all the way through! No borescope needed!