Well, here's the thing to consider (place on tinfoil hat if so desired....).
BP revolvers of the Ruger Old Army and M1858 Remington repros have never had 'paperwork' associated with them, i.e., no Form 4473. They're BP firearms, sold like vacuum cleaners.

You can obtain an aftermarket conversion cylinder for them, allowing you to shoot CAS - level .45 Colt rounds. I have two friends that have done that on a few, and they shoot great.
Just a consideration. Good luck!

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Ret'd LEO
SWCA #2275