Hi, Paul,if you click on "Full bbs collectors listing" and scroll down the posts, you will find scores (possibly hundreds)of posts re your rifle,one post(I think, by Troubleshooter) is a short history of the Service. Chris Thrale,s book"WEBLEY AIR RIFLES 1925-2005" has all the info about the service .Your rifle will have a single piston ring,not a washer.ATB Ray.