I have been through this before with a custom rifle maker........had my gun, along with thousands of dollars worth of others, and he flipped a screw, went bankrupt and shut his doors. There could be any number of explanations; I'd send a registered letter, return receipt requested and ask what the deal is. If he's reputable he'll get with you and make it right.
If no answer, or if he signs for it and doesn't acknowledge it, or refuses to sign, then you ( or someone else) need to show up on his doorstep and get your cylinder back. If still no luck, go through the State bar, find an attorney, and get the attorney to send him a nasty letter; most attys will charge a nominal fee (my state its $35) for a consultation and letter. If he is bankrupt, and shut his doors, moved, etc., you are out of luck. You can sue him, but if he's bankrupt, your finished.....and suing is way more than the cost of the cylinder.
Don't know the guy, but best of luck to you.
RR