I want to point out that more than a handful of states do their own background checks and act as the link between the NICS system and the gun shop.
My state doesn't charge to do background checks and has its own check system.
"States may implement their own NICS programs. Such states become the point of contact (POC) between their FFL dealers and the NICS. A few partial-POC states run FFL handgun checks, while the FBI runs long gun checks. FFLs in other, non-POC states access the NICS directly through the FBI.
Authorized local, state, tribal, and federal agencies can update NICS Index data via the NCIC front end, or by electronic batch files" --->>>
https://en.wikipedia.org/wiki/National_Instant_Criminal_Background_Check_System#Functionality
Another issue that I'll mention is that some gun shops may be concerned about liability or their insurance carrier policy regarding any crime or violation committed by anyone who they may sell a black powder or any other gun to, whether antique or not.
If a shop is sued, then they or their insurance carrier may still need to defend the suit, no matter how frivolous.
There may be other liability reasons why they want a record of who they did and didn't sell any type of gun to.
If the guns get stolen from the buyer or there's a false claim of true ownership than that also provides a record that a sale transaction occurred.
Why do they put serial numbers on black powder guns at all?
Doesn't it involve liability?
I've cooperated by filling out a Federal form for a couple of shops whether they are actually doing a background check or not.
I haven't bought one in a while, but I don't mind the paperwork as long as they're not charging for it.
I don't know what the local Cabela's is doing in that regard now days but I try not to let their red tape interfere with my freedom to decide what I want or don't want to purchase.
To me it's a business deal rather than a political football.
One local gun shop here has a sign that states that they can refuse a sale to anyone that they choose to which is hard to argue with if they do have that right.
If a shop doesn't charge for the check and still goes out of business then they've got more problems than how they manage their black powder and antique gun sales.
I've tried to be an equal opportunity buyer.