has anyone seen a P like this on a carbine stock before?

[Tuna]

It's RA-P for Raritan Arsenal which is the RA and then the P for the proof.

[Johnny P]

I had always heard that the P stood for the person in charge of rebuild/inspection. This month's American Rifle identifies who it was, Harry Petersen.

[Tuna]

It could be Johnny. It's what is listed in my reference material as being P for the proof and it's been wrong before.

[Johnny P]

Several of the arsenals used this with a slight variation. San Antonio Arsenal used C-SAA, and Benecia Arsenal had several variations such as BA-WK, BA-JL, BA-WL, and BA-JS. Springfield used a boxed version with the inspector initial under SA.