Can someone help me how accurate is the DPMS Panther Bull Twenty-Four Semi-Auto Tactical Rifle
And are they a good PD gun out to 400-500y and how are they in 204 or stay with the 223.

I had one that was very accurate out to 300 yds.

I never shot at anything past that. I went to a 10 round magazine and Harris bi-pod. Best accuracy in my rifle was with 62gr bullets.

223 is pretty well out of steam for 400 yds shooting, 204 isn't but it depends on what you're shooting at.

My .223 DPMS 20" Bull is an honest 1/2 moa rifle. 1" groups at 200 yards. YMMV.

The 223 w/8 twist barrel, 75gr MK's is routinely shot at 600 yards and often as not wins the match over other 30 calibers. Extremely accurate, economical to shoot, easy on barrels, little recoil, user friendly so to speak. Rapid prone shot in 70 seconds at 300yds. and concists of 10 shots w/ required magazine change. Not too shabby when some of the ten rounds are in an area well within the 10 and X ring and about the size of your hand. Good shooter can keep them in the 10 ring and several X's at 600yds slow fire, 20 rounds, 20 minutes. Oh, forgot to say that is not with scope, but issue sights/irons, prone/sling postion, no bags or rests allowed.