I like to have a cast bullet plinking load for every rifle I have, and the Handi Maxi is the latest. Most of the data out there is "maximum"; full of loads for H110, W296, 1680, and IMR 4227 .
I finally got a load range of 14 gr starting to 16 gr maximum of 2400 from the Sierra hot line, out of a Lyman manual. I'm using Lee's TL-358-158-2R, cast from RotoMetals Hardball casting alloy. It has a longer round nose and a higher BC than most 158gr cast 357 bullets, usually SWCs, which seemed appropriate for a rifle.
I worked up to a powder charge in the middle of the range, and seated my bullets unsized and lubed with Lee Liquid Alox, all per mfgr's suggestions...a new thing for me !
The first three shots at 50 yds were in 5/16th", the other two made a 2" group out of it, and the average velocity was 1666 fps.
I am a happy camper :-)
Although...seems that with both my 223 Ultralight barrel and the 357 Maxi barrel, most of my 5 shot groups have 3 or 4 shots very close, but alway there's a shot or two that opens the group up to 2 -3 inches. I'm starting to call it "The Handi Syndrome" ! Maybe should try one of those Limbsaver barrel de-resonators....