Sure, a shim would be worth trying. Or a little peg as you suggested - maybe it could engage a notch or groove in the metal ramrod tip. ML shotguns have little retaining lips that catch the tip - you pull the rod away from the barrels slightly to release the rod. Incidentally, it isn't a bad idea to use a separate loading rod for range use - a longer, unbreakable one is handy - and reserve the other rod for field use. And, if the load is going down tight, from fouling, etc. be really careful with a wooden rod. I've put splinters into my hand from a broken wooden rod. And that was a proper hickory one, not a hardware store dowel.