I've never had a problem with cast bullets in 30-30, 35 Remington, and 45-70 Marlins, all with microgroove barrels. I've been casting for these rifles since long before I started reading gun magazines and websites saying there was supposed to be a problem using cast bullets in such rifles. If your bullet fits the bore properly, and you are using a load that's correct for the rifle you're loading for, you should have no problem. I don't know if I'd call these rifles "not very cast-friendly" like Mikey does, but he's right in saying that it may require a bit of work--actually that's true for ballard-type barrels and cast bullets also. I've never firelapped a bore yet, but I have done some experimentation with bullet diameters, loads, and powders. Sometimes a good load in one rifle won't group quite so well in another. Unlike Clodbuster waiting for rhinos to shoot with his 275 grainers, I'm waiting for a Tyrannosaur to come out of the bushes to try my 420 grain RCBS flatnoses on when I'm carrying around my Marlin 45-70. Of course I may have to shoot twice since my boolits only chrony out at about 1875, not 2000. And that's with my gunshop owner's chrony because I don't have one myself. I just load for accuracy. Mikey thinks you can get there, and I do too. First thing though--slug your bore or have a gunsmith do it, so you'll know what the right size bullet matches up with your gun. Then experiment with powders and loads, shooting off a bench at your range. You'll get there. Keep good notes about the loads you try though. You'll want to keep the best one, and that one may not be best in another gun.