The one gun may have been stored in a way where the lubes in the gun made their way into the compression chamber. And yes with this situation it would be nearly impossible to group. Obviously this would explain the penetration which is far more than the 1000 series guns can do.
I guess if one of the seals was in real bad shape there could be a louder than usual noise b/c the air is escaping rapidly. The solution to this is a chronograph. Then you know if you are getting average velocities or not. With deiseling the velocity numbers will be high and very inconsistent. Usually they will be a bit cyclic. For example 910, 920, 925, 900, 915,915, 925, 900. It from the lubes burning partially, building up and then burning off more completely.
Good luck, hope you sort out the problems.