Nosler list H335 as the most accurate powder in the handgun section og RG #6. This would be a good starting point for you.
IMR 4198, TAC and Benchmark would also be good choices for the 223 Rem in a handgun.
Ya just gotta love those T/C Contenders. :wink:
A 10" Barreled .223 is a whole nuther breed of cat so to speak.
I have had a couple over the years, tried several bullets and several powders. I was finally able to obtain acceptable results with IMR-4198 pushing 40gr. Nosler Ballistic Tips. If I remember correctly I was getting like 2850 FPS from the 10" Barrel. I'd have to look up the exact powder charge but if I had to guess it would be 22.5 or 23.0grs.This load was surpisingly pleasant to shoot also.
Other powders and bullets produced good accuracy but velocity was sub par and muzzle blast and flash was horrendous.
I have worked with a lot of 14" .223's over the years and none of them gave me fits like the 10" did. Several powders work quite well in the 14" but not so for the 10".