What would be considered a good grouping on a 50 yrd mansize target.

I never got to shoot the m9 in the marine corp.

I tried it out at 50 yrd for the first and got all of my rounds accounted for. I say I had about a 10" group for fifteen rounds.

I believe that I can do better with a little more practice but I curious to know what to strive for.

Any PMI's I welcome Advice,

Semper Fi

Your 10" group isn't bad at all, but you could probably expect to shrink it to 4-6" with a load the pistol was fond of providing you where a very good shot. You're fighting a handgun that doesn't fit many hands well and a trigger that is decent but not match grade by anybodies standard. If you can shoot 5" groups offhand at 50 yards with any handgun you're a pretty darn good shot, let alone with the pistol you mention.