I have used my GSP .32 for several matches and shot it well.

My problem has been erratic grouping off sandbags - for some reason I
cannot seem to predictably hold a good group. I will be all over the
paper and then get a good cloverleaf. Is there an issue with
hold/follow through that the GSP may be subject to? Is it the way
recoil is changed with the gun on sandbags? My .22s and .45s I can
shoot dead center from the bags. FYI I do not have anything under the
butt of the grip - perhaps the magazine catches on the bags and shifts
the gun under recoil?

I have some factory Magtech ammo to use as a reference but am
confident that my handloads are quality.

Next thing I will try is resting my arm on the bags and not the gun.