Hey all. I acquired a Sig P320 in a tade. It came with two, what I assume to be, original magazines. 17rd, grey follower, round peg in the bottom. I also bought one new production magazine locally, black follower w/ square peg in the baseplate. First day at the range, several failures to hold open after last shot out of one of the original magazines. All rounds fed flawlessly, however. Never tested the second original mag as it was loaded with defense ammunition. The new locally purchased magazine had no problem. So, must be a spring issue. I ordered two new springs from Ebay. I compared the two new Ebay springs to the original springs in the two older magazines that came with the gun, and to the spring in the new production magazines I bought locally.
New Ebay spring next to old spring and follower:


New Ebay spring next to both old magazine springs:


New production locally purchased magazine spring/follower next to old production:


Obviously quite a difference. Do you think the springs took that much of a set if kept loaded? Guy I acquired it from said he had 50rds through it, and the condition of the gun suggests he didn't WAY underestimate it. Or, did Sig make a change in magazine spring length to combat an issue similar to what I experienced in later production models? Maybe my mags found there way into having lower capacity springs in them?

Hard to tell, but I was shocked at the difference in length.

Are those brand new springs that have never been cycled before? They will shorten up some after they have been used a few times. Simply keeping compression, even a great deal over a long period of time, on a spring isn't what fatigues them.

I know it is cycles that are supposed to fatigue them, not a constant compression, but the previous owner said 50rds through the gun. And it was in good shape so I dont think there is any way there was enough through it to fatigue the springs this much. That's why I'm confused.

I think the EBay springs may be incorrect. Possibly for a 21 round magazine.

I wouldn’t ever buy something off eBay that my life could depend on. No way. Of course I don’t think I’ll ever buy anything off eBay.

I don’t know anything about metallurgy or springs. But it seems to me that factory springs are kinda designed to be two springs in one. Looks like the section close to the follower is spaced more closely that the section by the base pad. And the gauge seems to thinner at the top too. By appearance of the two springs, I’d say that was intentional.

That all aside, you’re doing all this because you think it’s a problem with a mag spring not pushing up enough for slide lock. Does it lock consistently when you hand cycle? If so, try shooting left handed and see if it starts failing to lock. There’s a very good chance you’re riding the lever and don’t realize it. It’s not impossible that it’s the gun/magazine, but the most likely cause is shooter error (as it usually is with most things).

The ebay springs are the same length as the brand new, new generation spring from the sig mag I purchased locally. They are not plus power. All springs, short ones included, appear to have 12 coils. And my problem with the gun not locking back was isolated to the one old mag, the new mag did not give me any trouble. I'm well aware of the slide stops, I used to have a hard time with g19 slide stops not locking open, which I knew was my fault. Again, the p320 only struggled with the one mag.

My personal, limited experience with the P320 is that failures to hold open or unplanned lock backs are usually thumb interference during recoil or resting atop the slide release.

Some additional info on springs (Wolff). See Items 6 and 8:

https://www.gunsprings.com/ind...p?page=FAQ#question6

Welcome to the forum.