quite some time ago I posted some results using a variety of bullets from 210 to 250 jacketed in the 41 - both revolver and FG. I wish I could have more time to follow up on the loads but haven't managed it. You might try a search for my post. I had pictures of some of my targets. I'm guessing your 210 sierras might have been loaded a little light. I would expect you to get good accuracy from them - try a hotter load with 4227, 2400 or H110. Oh and the guy who makes jacketed 250 gr bullets, sells them on Ebay these days. Or find his post in the GB New Products forum. I think they worked pretty well for me. I want to experiment more. I'm hoping soon to put a Leupold 3x on my Marlin and get to workiing. My gun feeds 265 and 250 gr Corbons fine, also Federal 250 cast core fine and 265 Buffalo bore fine too. I think my gun really liked the Speer 210 gold dots. But try to find my post - my memory is poor.
Good luck. I really like my Marlin.