All store-bought lead .41 mag bullets that I've ever seen were sized .410 and Lyman (for example) doesn't show a .411 sizing (H&I) die, so the simple recourse to a larger size would be to use them as cast. I've always sized mine to .410 and they worked fine.
You bring up an interesting question. How come lead .41 mag bullets are true to size, whereas other lead revolver bullets are typically a thou. over, like .357/.358 and .429/.430? I don't know the answer.
You didn't say what weapon these were to be fired in. I don't know specifically for .41 mag caliber, but Marlin barrels often run a thou or two oversized. If you are fortunate enough to own a Marlin lever action in .41 mag, and need a slightly larger bullet, you could use your bullets unsized, as cast and maybe gain a thou or two. It's untrue that Micro-groove barrels are no good for shooting lead bullets through; the trick is to get the correct size bullets to shoot in them.
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