I inherited a Parker Brothers side by side.

[Dean Romig]

Some of the stamps on the barrel flats are as follows:

D = Damascus Barrels
4 (with superscript)1 = 4 lbs., 1 oz.
3 = Grade 3 or D Grade
1 on the bottom of the rear barrel lug = 1 frame or a light 12 gauge.

As for the 'checkering within the skeleton steel buttplate... someone with a knife decided to "enhance" the original checkering. It is not at all how that checkering would have originally been done.

That rust at the muzzles may clean up but first that rust must be neutralized ASAP.

[kaneporter]

That rust at the muzzles may clean up but first that rust must be neutralized ASAP.[/QUOTE]

Is there anything u recommend to treat the rust?

[edgarspencer]

That rust doesn't look all that bad. Rust is between 3 and 6 times thicker than the metal sacrificed in generating it. That, and that it's at the lowest pressure point on the barrels means with a small amount of striking, it probably won't even show up when the barrels are refinished. Rather than straight motor oil, I'd soak it in a dilute mix of motor oil or ATF with kerosene and a dash of acetone. In it's quest to consume the oxygen in the rust, the acetone will pull the oil/ATF in and lift the rust up, making it very easy to scrub away.
That's some pretty neat butt checkering. I'd guess you would measure it in lines per foot rather than lines per inch. It does seem to be done pretty parallel so it might not be that difficult for a guy like Brian to straighten out.