i would make sure its legal to own first. its what the atf calls a SBS (short barreled shotgun).
Short barreled shotguns (SBSs)—this category is defined similarly to SBRs, but the barrel must be at least 18" instead of 16", and the barrel must be a smoothbore. The minimum overall length limit remains 26".
my understanding with the contenders is that if you put a rifle buttstock on it, it becomes a rifle. in other words if you have a contender with a 14" 30/30 barrel and put a rifle buttstock on it, you're breaking the law.
i would consult with the PSP to be sure. your timing may be bad though.
My diploma is a DD Form 214