Sig P220 Slide Locking Open Prematurely

L

LIProgun

New member
I had a student at the range shooting an older Sig P220 in .45 ACP. On his fifth shot from a fully-loaded 7-round mag the slide would lock back almost every time.

Inspection revealed the top cartridge was not hung up or depressed in any way. It appeared that the slide lock was simply engaging each time, and either depressing the slide lock or retracting the slide chambered the top round each time. The last two rounds fed fine.

At first I thought the student may have been hitting the slide lock with his thumbs, but I ruled this out by observing him. It also happened only on the fifth round, which I found pretty odd. The phenomenon happened with two different mags, both of which were in fine condition.

I field stripped the gun and saw absolutely nothing wrong. The gun was relatively clean, and properly lubed.

Ammo was a handload using 230 grain cast RNL at about 800 fps that has a flawless track record.

Any insight into potential causes of the malfunction would be greatly appreciated.
 
A friend had the same kind of problem. Turned out that the slide lock tab was just a touch long. Recoil would slightly walk a round in the mag and the nose of the round would engage the slidelock. The problem went away with a different bullet profile. Next time this happens take the mag out and inspect the top round. If it shows contact,lightly file or stone the slide lock tab area that makes early contact. Work slowly and carefully. Hope this helps.

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Be careful what you ask for..You may get it.
An unloaded pistol is a paperweight.
 
This may be more of a magazine related problem than a slide lock tab problem. I would try a couple different mags using the same bullet profile and see if this helps before stoning things. I hate to stone or file anything until I rule out all other posible causes.

If the problem is rounds moving forward under recoil, you may want to install a new stiffer spring in the magazine. If it's an aftermarket knock off, you may want to trash that puppy.

Regards! DaMan
 
Dug out my SIG armorer's manual, circa 1990. Under 'Slide is arrested before last round' it says the cause may be a weak or broken slide catch spring. Remedy is to replace spring and/or slide catch. In checking my fairly new 220 I find that approx 8# of pressure is needed to raise the slide stop 1/4" up, and it should snap back down smartly. It is just possible that if someone unfamiliar with the detail stripping had the gun apart, they might have broken, bent, or misaligned that spring (which installs next to the locking block and can be difficult).

In addition I would also be suspicious of any non-SIG magazine and vary the ammo just to eliminate that source as well.

Only time I ever had this problem was on a LW Colt Commander, and it was a bullet-slide stop interference problem. In this case, I would check the slide stop spring action. Good luck.

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