Zermatt7,
The Magbolt/Hunterbolt line of rifles suffer from the same finikyness that most guns suffer from, i.e. they require you to taylor the load to the gun. My brother has one with a 24" barrel that seems to like lower weight bullets (around 250+/-). I have the 26" version and it likes heavier bullets(over 250 for sabots, over350 for conicals). Also I have found with mine, the more I shoot it the better it shoots. I now (after maybe 300+ rounds) find that it likes quite a few different bullets in the 250 to 460 range. The most accurate is the 348HP powerbelt which routinely groups under 1" for 5 shots at 100 yards using 100gr of 777 2F. The 300SST's also group around 1" using 130gr of Pyro pellets. The 250 Shockwaves also do well with several powder charges between 80 and 130 grains. I even get good groups shooting patched round ball if the patch is tight up to 80 grains of 777.
The best thing to do is first verify the stock, barrel and scope (if you have one) are tight and not causing problems. Next, get several different bullets of different sizes and, using a good rest to minimize the you factor, go do some shooting. Most guns will shoot well in the 80 to 100 grains of powder range with pyrodex so start with that and shoot groups with 80, 90 and 100 grains of powder to see what your gun likes with each bullet. Swab between shots with a slightly damp spit patch or with alcohol/windex then a dry patch, clean between bullet types for consistent comparisons. Somewhere in there you will find something that works, then you can start fine tuning if needed.
Don't rush the process and let the barrel cool between shots (this is a great time to get some practice with a 22 or whatever between shots). You may want to limit the testing to 1 to 3 bullets per outing. You can shoot at 50 yards to save on the walking and will still be able to recognize the differences in the loads.
Good luck and above all, have fun.
