577/450 Maxim

This 1897 Maxim had “EXP” written on it when I found it. Any opinions?
How rare are the “MAXIM” headstamps?

I suppose the writer of the “EXP” assumed to to be experimental, but it was not as it was a production item.
The headstamps are not rare but a long way from common.
Here’s a headstamp variation.

Thank you Pete!