4.25 Inches makes it a commander size if I'm not mistaken. According to the Wilson recoil spring selection chart the spring spectrum should be between 12# for light loads to 20# for major loads. Check it out just to be sure: http://www.m1911.org/technic1.htm
Edited to fix URL.
[This message has been edited by malmon (edited 10-31-2001).]