I spent a few mornings with the GM barreled 25 cal and got pretty consistently 1.25", 8-shot groups. I re-barreled with a BSA barrel and with very limited time, and failing light I got just under an inch. I am confident this can be improved upon with better driving on my part. Another advantage to the aftermarket is ability to get them longer. For what ever you decide upon, get it as long as you can; efficiency goes up...