I've noticed a much heavier spring weight in one of my M18/P320 pistols. No differences in shooting but one is heavy enough to make it more difficult to lock the slide back that I've ordered an extended slide stop for this pistol.

Any ideas regarding the differences? Any replacement spring recommendations should I eventually do that?

(I'd post a photo of the springs but can't figure how do do it.)

-- Chuck

Check with Wolff or ISMI for spring technical assistance.

You can convert M18 (and Full size) to take 1911 recoil springs.
"Convert" is a big word for this. You simply change from a captured RSA to an un-captured RSA.
It makes recoil tuning possible and it's more economical to replace a $7.00 spring as opposed to a $39.00 OEM captured RSA.
All the P320 Shooters in my orbit have switched to 1911 springs.

https://www.armorycraft.com/pr...xg-recoil-tuning-kit

How to tune :
https://youtu.be/xUecHstU4QQ?feature=shared

This message has been edited. Last edited by: DirectDrive,

SIG commonly marks their pistol recoil springs with different colored paint for the different cartridge chamberings. The usual color for a 9mm P320 is orange, and green for 357 SIG/40 S&W. Do your springs have colored paint on them?

As for posting photos, a discussion here:
https://sigforum.com/eve/forum...935/m/6470098434/p/1

Thanks, guys.

(I'd have thought we were well beyond having to link to a "photo site" but... )

No paint on any of the 3 recoil springs. None were loose and came in complete pistols or slides.

The two "lighter" (feeling) spring sets look identical, have flat wire outer springs and braided wire inner. One of these springs is from my 2017 (since been to Sig and back) P320 Compact. The other is in a (claimed) complete USGI M18 slide with both the Mfg and Part No. on the slide and barrel.

The heavier spring (the one that prompted me to get an extended slide stop) has a brass colored cup (?) where it enters the front of the slide followed by round wire outer and inner springs. This came with a complete 2025 dated commercial M18 (slide only marked M18 (no P320 marking) and the Mfg, but not the Part No. FCU M18A prefix serial number (I know this isn't a USGI serial).

Matter of curiosity really, the pistols function perfectly regardless of the recoil spring.

-- Chuck