Need to find serial # the gun is in great shape and the last patent date is Aug 19,1913

I am sorry, you need to find the serial number? I am not sure I understand what you mean. Isn't it on the gun??

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John Caradimas SV1CEC
The M1911 Pistols Organization
http://www.m1911.org

Right side of frame.

The patent date on the slide is meaningless to you being that serial numbers are on the frames. All 1911's in this era will have that same patent.

If there is no numbers on the frame, you're at a dead end. It's not impossible that a G.I. brought it back from war and scrubbed off the serial number so no one could track it.

Depending on when it was made it might have a serial number stamped under the firing pin stop. Since slides are often exchanged that serial, if there is one, might not be the actual serial number of the frame.

Thank you and i think your right about the GI thing