DCMatt, I also think that's a crown with a number or letter below it. And the P bothers me, but I can't find another on the internet either. I'm certainly not an expert on proof marks, and have never thought the US on guns to be a proof mark, but rather to show ownership, like for instance, the US on the military model 1911. I have a Bridesburg contract Springfield rifled musket up stairs, and I'm going to have to get off me dead butt and go look at it. I know there is a P proof mark on the barrel of my 73 Springfield carbine. A Harpers Ferry butt plate has a notch for the patch box. My swag right now is it's off a Lorenz imported from Austria. The crown and the writing on the butt plate just doesn't look Springfield to me, but I've certainly been known to be wrong more'n once. I'm saying Lorenz and I don't even know if for sure that gun has an iron or brass butt plate. When Tejaas gets his records he might be able to shed more light.
As i stated above, i believe the "P" to be an assembly mark... My generic use of the term "proofmark" to also include arsenal/assembly/inspector/property marks didn't allow me to accurately convey my point, and I apologize!
"US" is indeed a mark indicating Federal Service conscription.
Firearms purchased FOR the confederacy BY the confederacy would lack the "US" identifier.
Firearms UTILIZED by the confederacy would display markings that endlessly varied... we all know that a confederate wouldn't pass on a Springfield M1861 laying on the field of battle!
Pennsylvania had a lot of confederate troop movement. We all know that!
Confederates for the majority supplied their own weaponry and "traded up" through various means at the first available chance. That is also well documented...
So if this is in fact a buttplate off a Springfield M1842, who's to say it wasn't a privately owned piece brought along from home when the owner went off to fight for the cause? That could explain the lack of a "US" marking, it never was federal property to begin with!
It could also be a Union army piece! Again, if it is a buttplate from a M1842 it's obviously pre-war... A whole lot of firearms were donated or leased to the federal army via military academies, home guards, and state militias. This could also explain the lack of a "US" mark... And quite frankly the slew of letter and number stamps on the plate would be consistent with company/rack/weapon numbers of these institutions.
Lastly, the possibility of this being from an Austrian Lorenz.
I mentioned this much earlier in this thread... GREAT suggestion!!!
I was quick to discount this however, as although the buttplates of a Lorenz and M1842 are near identical... This buttplate lacks the Kaiser Double Headed Eagle stamp that Vienna stamped in. And as I compared earlier to the Swedish M96, Vienna was notorious for stamping EVERY COMPONENT!
You may say "well, everyone knows that imported war contract purchased arms are known to be lacking a lot of the usual foreign-applied markings!"
The Lorenz was "scrubbed" before export from Austria... Namely most if the Lockplate stamps. But the Kaiser Eagle remained. Believe me or not, I quadruple checked my references.