I have a .58 which will shoot RB's with acceptable accuracy, but it's no tack driver. And I NEVER use Pyrodex in anything I own since many far cleaner non-gunmetal destroying powders are available. I'm partial to the OLD Black Mag 3 from Arco Powder Co. Liked it enough to buy in sufficient bulk that I still have 2 1/2 lbs.
The new Magkor stuff I've not yet tried, but the maker tells me it's much the same, but a bit more energetic. The old one is cleaner than any smokeless I've used in my cartridge guns!
Range sessions with highly hygroscopic Pyro were really messy, liquid ooze running into the breech through the flash hole when swabbing the bore. Swore that poison off for life!
The .58's were twisted a little too fast for perfect ball shooting. I've seen twists for these stated variously from various writers all over the posts, but mine measures out at 1 in 66''. H&R may have tried different rates during the tenure of this model, so patch yours to find out what it is. If it's faster than 1 in 66'', don't expect much from round balls in terms of accuracy. A .58 roundballer is happiest somewhere around 1 in 80''.
I used a 100 gr. charge of propellent and ox-yoke wonderwad with mine.
For ignition I dumped the no. 11 nipple, replaced it with a 209 holder from
www.hubbardsoutdoorproducts.com which fits the push-in breechplug on mine and more than likely your screw-in one, if you feel so inclined.
