59 slide locking open

[That One Guy]

New guy here. Been reading the forums for a few months and finally decided to join up.

So I recently got my hands on a 59 in excellent condition. Also managed to grab a few original factory mags for it. I field stripped the gun and cleaned/lubed it as soon as I got it. I disassembled all 3 mags and thoroughly cleaned them as well. Took it out for some range time last weekend and had a blast shooting it. The gun is very accurate, much more so than my 639.

The only problem is that the slide locks open before the magazine is empty. It happened exactly one time with every single magazine I ran thru it (about 150-175 rounds total). There was no rhyme or reason to it that I could tell. Sometimes it would occur in the first 2-3 shots, sometimes in the middle of the mag and sometimes the last 2-3.

Fwiw, I was using the same ammo the whole time and it worked just fine thru my 639. I also made sure it wasn't my grip on the gun causing it. Not sure where to start looking. Thanks in advance for your help.

And since someone's probably gonna ask...

 

[Dandecoteau]

Welcome to the place you will spend most of your time.

I would say your limp wristing from what it sounds like.

It may sound like an insult, but how much firearm experience do you have? Improper grip can make an autos slide lock open prematurely.

 

[RaylanGivens]

Limp wrist

Welcome to the place you will spend most of your time.

I would say your limp wristing from what it sounds like.

It may sound like an insult, but how much firearm experience do you have? Improper grip can make an autos slide lock open prematurely.

I have to go with this theory. I've read this issue on this forum several times, most usually about the first generation semi automatics.

 

[That One Guy]

I definitely don't take that as an insult. I've seen plenty of other people do it, so it would have been my first guess as well. I hope this doesn't come across cocky, but I'm very confident that I'm not limp wristing it. I've been shooting handguns for 30+ years, autos for 20 and I've never had this issue before.

I played around with my grip to make sure that wasn't the issue and also to check that I wasn't inadvertently hitting the slide lock. Nothing I did made a difference. It did it to my dad as well when he shot it.

 

[FPrice]

I wonder if the recoil spring may be weak. Could a weak spring allow the slide lock to catch prematurely.

 

[jimbo728]

Check the tension in the slide stop pin spring. Compare it to the 639.
it could be weak or broken which could cause a bit of movement up in recoil.
jim

 

[HCH]

Could you be gripping the gun so you thumb up the slide stop while shooting?

 

[That One Guy]

Could you be gripping the gun so you thumb up the slide stop while shooting?

No. Even shot it left handed just to be sure.

Check the tension in the slide stop pin spring. Compare it to the 639.
it could be weak or broken which could cause a bit of movement up in recoil.
jim

A completely unscientific mashing of the pins with my fingernail indicates that there is no discernible difference between the two.

 

[That One Guy]

Ok. So After after a bit of poking, prodding and cursing, I feel pretty comfortable calling this an ammo issue. The one on the right is what I was using. They are "factory" reloads I picked up at a gun show. For comparison, that's a Federal something or other standard FMJ on the left.

Here's what I think is happening...
Take note of the short, round shape the of the red bullet vs the taper of a regular FMJ. The shorter OAL is allowing the rounds to ride forward in the magazine which puts the fatter bullet right against the slide stop. I eyeballed the clearance with a couple rounds in each mag and there was zero discernible clearance between the red bullet and the slide stop when the rounds were moved to the front of the magazine. I should mention that I never had any issues with the first 2 shots fired. Also, whenever the slide locked open I did notice that the rounds had moved to the front of the mag.

IMO, All these things seem to point to it being an ammo issue. All that said, I can't get to the range for another week or 2 to confirm this theory. As soon as I do, I'll update here.


BTW, sorry so wordy.

EDIT: Sorry the pic is gone. I accidentally deleted when I was cleaning up my photobucket the other day.

 

[paulj84003]

There is another reason the slide stop will pop up and lock the slide back. A slide stop Button that is loose, front face straightup or leaning slightly to the rear. The button is staked in at the factory and is supposed to tilt foward at the top a couple of degrees.

 

[jimbo728]

Your ammo theory is sound. Some bullets can push on the slide stop lug as they are pushed up the mag. I hope you find a bullet that clears the slide stop and will still work in your 59.
Good Luck
Jim

 

[That One Guy]

I checked it with the Federal FMJ's and there was plenty of clearance. These reloads were only $10/box at the gunshow from a local guy. Next weekend when I see him again I'll splurge that extra dollar a box and get the standard profile FMJ's that he has.

 

[That One Guy]

Wanted to update this thread, as promised. Finally made it to the range last weekend and put another hundred rounds thru the 59. This time I was using run of the mill Federal 115gr FMJ's.

I had zero issues with the traditional shaped ammo. I also ran one mag of the original ammo that I had trouble with, and the slide locked open before the mag was empty.

I guess it's safe to say that it was indeed an ammo issue. The real bummer is that the ammo that gave me trouble was very accurate in the 59, and it shot to POA. The Federal stuff, well... it was a lot like patterning my 870.

 

[JudgeColt]

paulj84003 has hit upon the cause of the problem. On any 39/59 pistols I personally have or have heard about with this problem (some law enforcement friends back in the day), the solution has ALWAYS been to slightly turn the "slide stop button" (as paulj84003 calls it) so that the slope is such that the slide stop tends to be pushed DOWN by the slope as the spring-loaded stud rides on the slope.

The reason the problem occurs with some ammunition types and not other types is because of the shape of the bullet. The more-pointed 115-grain FMJ bullet does not come into as solid of contact with the slide stop protrusion inside the magazine well as other bullet shapes, so the slide stop is not so likely to be "pushed up" as with other bullet shapes. This can be seen by removing the slide, reinstalling the slide stop and inserting a loaded magazine into the magazine well. The potential contact (or lack thereof) by the bullet with the slide stop can be seen. Adding resistance to the slide stop from being "pushed up" by turning the "slide stop button" to slope more will allow the slight contact with the bullet as it goes by during feeding to not engage the slide stop.

Obviously, if the "slide stop button" is loose, it will have to be re-staked to tighten it so that it will not turn on its own. Then adjust the "slide stop button" slope until the problem is gone for good. (Use a small adjustable wrench tightened against the flat side of the "slide stop button" to turn the "slide stop button" as necessary.)