I think the problem is with the target....
Some of these targets have good eyesight and can tell if they are being shot at by a high quality gun or not. In the case of the Colt, the target was probably not concerned about it so sat still, giving the Colt a fair opportunity to tag it from time to time.
I'm absolutely sure that when it saw the Highway Patrolman come out of the bag, it started jumping side to side (can be very subtle to the shooter) just at the time the trigger was pulled.
These things can be very wiley about such things....

Or, maybe it's the difference in ammo as suggested above.
I'd tend to think it's my explanation that is correct, but then again I'm biased.

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.............SmithNut