some of this wont apply and some will sound silly, but take what you can use.
a bud sent back 3 CM units for drift. we were loading out side at a match and he asked if i had a cord so he could use his truck battery. i hooked him up so he could get off of 110v power but he still could not...
i have personally bought 2 rifles that would not shoot. cheap.
a good cleaning turned them into great guns. one did require taking the trigger apart and soaking the pieces in solvent for a few days.
step son had problems with a custom barrel and took it to his smith. the smith took a look and put some scotch Brite on a short cleaning rod and chucked it in a drill. he almost panicked when the drill was inserted in the chamber but in a few seconds the ring was gone.
another experimenter...
you do need purpose --- more than the Indians wife, who was named three ponies, can give you.
" so why if she named three ponies??"
he replied "nag, nag, nag,"