What is this marking? Brass end plate

Hi all, I have this laying around in the garage.
What's the marking and what is it likely to be off?

Thanks in advance.

Attachment 166437
Attachment 166438

303 butt plate

Quote:

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Originally Posted by Frogfeatures

303 butt plate

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Thank ye

SS stands for sold from service

It's from either a long lee enfield or lee metford.