When you go to the P38forum...check out the tech info section on the opening page.
Your gun was made by Spreewerk in March 1944. It is the most common of all P38's.
Is the '172' the number on the frame under the left grip?...
What is the letter/number on the right side of the barrel? [usually a B followed by a letter or number]
Orvel L. Reichert
P O Box 67
Vader WA 98593-0067
quote........ "Every gun that is made, every warship launched, every rocket fired, signifies in the final sense a theft from those who hunger and are not fed, those who are cold and are not clothed." --President Dwight D. Eisenhower