Smith and Wesson Top Break!

So my Curmudgeon at large whips this out last weekend. Says he has had it for over 30 years. Wants to know if I can find anything out about it. I'm in over my head here. All I can find is serial numbers on the cylinder, top of the back strap, and butt. They all match. 

There are patents stamped on the top of the barrel. First patent seems to be Jan. 24 '65 and reissued with the last date Jan 03 '82 (I think). Hell even the big honking magnifying glass is letting me down! 

Big pictures! Click to enlarge! 

 

It will not go in to battery. It has a small bulge slightly over half way in the barrel. I don't even know what caliber it is. 

So what to do? You know I want to fire it! Clean it? Leave it alone? I know I can zip some money to the S&W Historian to find out more but I thought I would ask for some help here first (*cough, cough, Tam*)! Any would be appreciated! 

Oh the Curmudgeon has a lap top and stalks constantly! Typing is not his thing! 

Thanks again for any help you can offer!

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