At the 21gr. load, it sounds as if the pressure TBoss is generating, exceeds the strength of the bullet by too much and may be bending them before they are entirely inside the bore. You could try seating them out as far as possible, or merely trying a different, slower burning powder.(so the bullet is totally within the bore before the powder peaks pressure).

Although it developes low velocities, it is a common mistake to think TBoss is also a low pressure powder. The full case you are using is probably in the 30,000 to 35,000 psi range. In this case, it might be peaking too early.

Dropping to an H4895 load, what is it? AR2206H?, might give what you desire. Varget will also work, but I prefer H4895(made in Australia by ADI). I also loaded 45 to 50gr. in mine and got very good accuracy with 500gr. in my rifle - in the 1,500fps range- similar ot a .45 2 7/8" Sharps loaded with 120gr. of black powder & 500gr. bullet. Regular primers can be used, but with reduced rifle powders, I used WW, RP or CCI magnum primers. It didn't seem to matter which. With less than full capcity loads, I used KAPOK between the powder and bullet -(you can use a card wad under the bullet if no gas check, will about give gas check results). You can even use a gas check upside-down on a full case of powder if you want. The whole reason of the gas check is to seal and prevent gas cutting.

The KAPOK and card wad do that as well in less than full case loads. If using a filler - any filler, it should/must fill the empty space.