Trapdoor Rifles

At a gun show yesterday, I saw what appeared to be an 1868 Springfield but it had no serial number, the rear sight was a musket sight or 1866 rear sight and it was placed way further forward on the barrel. There were no signs of modification or holes where the sight was moved and it was definitely an 1868 receiver with an 1870 block barreled in 50-70. The front sight was a standard musket, cleaning rod was standard 1868. Is this a banner man made gun? I almost bought it since it was pretty cheap and a decent bore but I’m typically more into correct military configuration guns and ended up buying a mint Remington rolling block military rifle, in .43 Spanish (unfortunately).

Yeah, it sounds like a Bannerman.
I’ve seen another just like that for sale on Gunbroker.

I’m glad I knew enough not to buy it, even though it was a good price even for a parts gun. Thanks for the reply!