The term usually refers to GENTLY changing the curve of the lips of the magazine to improve feeding. Usually by bending.
Contact High Standard with the Serial Number and they will tell you when it was manufactured.
BLue Book of Gun values
I own a .22 High Standard Victor and owned it for over 30 years. I have put over 30,000 rounds through it. I have the 4.5 and 5.5 inch barrels. This is the most accurate pistol I have ever owned. It is easy to clean and shoot. J.C. Beaver, OH
The Supermatic Trophy used the ML prefix from 1951-1953.
The only way to know is to try with you specific weapon. Some will, some won't.
High Standard.
No way to know without trying.
Good 22.
100-1000 USD
1,000,000,000
1970
1974