"Simply because a rifle is a hammer gun, does not mean it was not a nitro rifle!"

And also vice versa,

Simply because a rifle is a hammerLESS gun,
does not mean it is a nitro rifle !

English guns need to be checked.

I agree, it is almost certainly a nitro proofed gun.

You did the right thing coming on a forum and asking.

Sounds like you have a winner.