[gunsrfun1]

This may not make any difference, but since I have the gun apart for cleaning, I may as well ask. This is a National Postal Meter M1 carbine that I have not fired yet. It came with a 10 1/8” recoil spring, but I have a 10 1/4" spring that I bought from a gun show. Both are in the same good condition, although the original spring is silver-colored and the gun show spring looks blued or something. Does it matter which spring I use, since I am leaning toward leaving the original one in. Is there a "factory spec" size? thanks

[loadedround]

I've done a lot of work on carbines and don't think it will make any difference on which spring you use. I measured 6 surplus springs I have and they all fall into the same parameters of yours.

[AZ Jeff]

The difference in spring lengths you cite is 1/8 of an inch in a spring of overall length of 10 inches plus. That's less than 1.5% difference. I would guess that a 1.5% variation is within manufacturing tolerance when the spring was new. It's CERTAINLY within tolerance on a used spring.