Greenmonsters
Wannabe Duck Boat Owner
In my experience , the condition of the composite bats makes a huge difference. When new, they barely hit at first before broken in, then they get good, then eventually they get really bad, probably when develop fine cracks. The sound is not a crack anymore but a dull thunk. DD knows the difference for sure, by feel and sound. She normally puts around 4 out of every 5 balls over fence in bat practice. When it barely gets halfway to fence on most, on well hit balls, theres something wrong. Change bats, problem solved.
IIRC, you mentioned machine BP w/ the poly balls. Varies by brand, but some are very dense (for durability purposes) and prone to shorten bat life such that most makers claim that it will void their warranty. IMO, best bet is to save the gamer, and just hit a dead one of the same wt/length in BP realizing that performance will improve w/ the gamer. Actually, you may want to try a slow pitch bat as they tend to be more durable.