105mm M14?

This is way out of my area!! I recently picked up a 105mm M-14. It’s old and dirty! What I can make of the headstamp is:

                                    105 MM. M 14
                                         TYPE 1

                                         LOT NO.
                            138-23139-1 M.M.C. 1942

There is also a mark at 9:00 I can’t make out and marking on the prime I can’t read because of the dirt and corrosion.

Who made it and whats the best way to clean it up (or should
it leave it as is)?


It is a very common (at least here in Europe) US made 105 mm Howitzer shell case from WW2.