clearly there is technology form much after 1800 going into many of the PA legal flinters
An interesting statement, please give examples.
https://www.traditionsfirearms.com/category/PA-Pellet-Ultralightwell specifically I meant the PA pellet rifle a Gun made by traditions to be PA legal but fire pyrodex and 777 pellets it uses a kicker charge but with plastic stocks , the locks look 1800s but the internals of the breach plug are supposedly a newer tech to light off the pellets.
the other clear change was that music wire springs were not common pre 1800 but they would be quite common in modern locks they are hidden behind the plate from plain view.
also cerocoate and stainless , plastic sights , fiber optic sights
rubber but pads
so it is in the Spirit of 1800 but not really the strict detail
most triggers pre 1800 would also have been single set meaning you had to push the trigger forward to engage the sear most triggers put on muzzle loaders in the last 50 years have a trigger return spring gain music spring technology not flat springs common pre 1800
I don't see anything wrong with these things the spirit of the law is one barrel slow to reload but when you say nothing past 1800 and then guns have "modern" features and technologies that didn't exist in common practice before 1800 it is n't really the letter of the law is it.
the percussion cap being patented in 1807 does set the use of caps out of bounds and I think that was the real intent , force a pre 1800 based ignition system.