Model 121 - Identification of extra markings on barrel?

[CaptLouie]

I have my fathers old Field Master Model 121 pump (with a redfield peep sight mounted).
Great for flipping squirels off limbs on lazy summer afternoons.
Serial number is 1694nn
Manufacturing info indicates October, 1951 (EXX).

There are additional stampins following the manufacturing information...
Total stampings appear to be (EXX 5P)?
These don't seem to match up with the ID info I've found on this site...
... unless the (5P) are ?assembly? identification...

I've had several people check the stampings, they all agree they appear to be (5P)...
...I thought they might have been a badly impressed (SB)?

Any thoughts or assistance.... GREATLY appreciated.

Thanks...

[John Gyde]

Those are just proof/testing stamps.

[CaptLouie]

Thought the Proof Stamps were on the other side of the barrel...
I'm just going by the info under "manufacture date" >> "barrel code identification markings" diagramy on the main web site...
Their diagram only shows "assembly" following the manufacturing code...?

[John Gyde]

You might find stamps on either or both sides of the barrel. There is a number (maybe 5) that denotes an employee sale. I don't have my records available while I'm in AZ so I can't be sure. If so, the P would be a mystery. My bet is that they are just more proof/testing stamps. There should be a symbol; probably on the other side of the barrel.