Hey there Navygunner. I have a Mustang and have maybe 2000 shots out of it with a wide variety of bullets/sabots/powders.
My best shooting load is a 300 grain bullet (Speer Gold Dot or Hornady XTP) in a Harvester sabot (H5045SB or H5045LB) over 105 grains of Triple 7 FFFG. This load gives me 100 yard groups in the 2" range and has a muzzle velocity right at 1800 fps with the chronograph 15 feet from the muzzle.
I have a Leupold 3x9 scope on my gun and do a lot of shooting from a solid bench with Caldwell front and real rifle rests. I've never been able to find those "one ragged hole" groups with this gun. It's no target rifle but gives me decent hunting accuracy. Overall, I like the gun.
I've never tried TC conicals out of mine, but did try the Hornady Great Plains and was able to get those to group into 2" at 100 yards also. But I had to keep the velocity way down to around 1100 fps with a light charge. If I boosted the charge the groups would open up to four or five inches.