Troubleshoot Tuesday!

[1911Tuner]

Troubleshoot Tuesday!

Here are the issues.

Norinco with freshly refitted slide/frame. Occassional failure to lock slide on several good, 7-round magazines that have proved dead reliable in other Norincos and Colts. Intermittent problem that could occur with any one of 36 magazines...or not. Followup check didn't reproduce the malfunction. (No...This isn't kartracer's Nork. It belongs to Kelie's ex.)

The problem:

The follower shelf climbs on top of the slidestop lug, failing to lock the slide on empty and sticking the magazine in the well until we'd pop the stop to free up the shelf.

The problem doesn't recur when hand-cycled. The problem doesn't recur
on the same magazine when retested three times.

Installing the slidestop into the frame and inserting a magazine revealed the problem, which was partly due to the slidestop pinhole being a little past at the high end of spec on the rearward location
when compared to several Colts and other Norincos...and partly due to the magazine follower shelf geometry...which causes a problem only in this pistol. In other words...a tolerance stack issue.

The magazines are Metalform. The slidestop is a USGI takeoff...likely Ithaca.

Identifying the problem took 15 minutes. The cure took less than two.

Tic-tock...

 

[Knucklehead2]

Maybe, not sure

but filing a wee bit of stock off the protruding into mag space of the slidestop? Toward the rear, maybe a slight bevel also on the groove to help the mag follower enter the slot? I am guessing that may solve the out of spec problem of the pin hole.

 

[Knucklehead2]

Second part of description

downright incorrect. I just looked inside, forget the slot. its just a shelf on the slidestop and gets pushed straight up. I have a lot to learn!

 

[1911Tuner]

re:

Very close, Knucklehead...

 

[Knucklehead2]

One question

I would ask, my assumption that the slidestop itself is in tolerance? Maybe the farthest (backside) from the pin hole part of the slidestop is interfering with the step in the mag follower? I need a spell checker!

 

[1911Tuner]

re:

Wooohoooo! You is SMOKIN' hot, Knucklehead. You seem to know your way around a 1911 pretty good. The stop is in-spec. There are three issues at work. Two are primary causes...the third is secondary, but part of the whole.

 

[ribbonstone]

Have had one that would move a bit out as well as up....was an issue with the little slot the detent was supose to ride in. Slot wide...detent's point narrow.

 

[1911Tuner]

re:

Ribbonstone...Nope. The slidestop itself is fine. Detent is doin' its job.
The location of the slidestop pin and the follower shelf geometry(<---CLEW!)
was the main cause of the problem.

I'll go ahead and describe the third one, just to be fair. Note that the problem would likely have occurred even without this one...but it was a contributor.

The bridge across the slidestop cut was a trifle small in the radius. The slidestop lug was being pressed tightly against it whenever it was pushed up by the follower shelf. This aggravated the problem, and probably caused it to occur more frequently...but it wasn't the main cause. The clue on that one was the stop falling just a little short of full engagement. When I opened it up a bit..maybe .010 inch, it was removed from the picture...but the other problem was still there.

Knucklehead's all over this one. Wouldn't surprise me if he busts it.

 

[Knucklehead2]

While I was gone

I was looking at some prints and Tuners last reply just shot my theory down.
I'll say what I was thinking, the location of the pinhole can be out .008 so maybe it is hitting where it goes through the frame. But if the arch was already filed that can not be it. Soooo I will have to say that the geometry of the slide stop is not hitting the follower correctly. I can not see how it would hop over the follower but I will have to think about that some more.

 

[1911Tuner]

Theory

Knucklehaed...Don't give up now! You're so close you could almost hear John Moses sayin' "Yeah!"

The way that the slidestop lug is contacting the shelf is the problem...and not the lifting part of the shelf.

Clew:

The underside geometry of the lug...the part that the shelf contacts to lift it into engagement...is correctly angled. Think...Think...You're so hot, if you'd fall into a barrel of kasenit, you'd come out case-hardened.

 

[Knucklehead2]

I was thinking

more of the other geometry. As you know the slidestop has angles, and radii all over it. Including the two angles on the bottom. But if the holes were located to far back that would put the 25 degree angle up against the leg in the follower.
I am rusting my firearm breathing on it so close! No loupe, so I am holding a magnifying glass in one hand and a mag light in the other, but I can not see how the follower would jump. I can see how it could interfere, and the shelf (follower) would not touch because the bend would hit the 25 degree angle on the slidestop first.

 

[1911Tuner]

re:

Knucklehead...The only thing that's kept you from nailin' this one is not havin' the gun in your hand to see exactly what it does. I'm gonna go ahead and declare your victory and give the explanation.

The pistol belongs to my Signifigant Other's ex-husband. (Long, interesting story.)

The shelf is bent into an "L" shape, with the vertical piece at nearly 90 degrees from the top, and the horizontal part at 90 degrees to the vertical.
This follower's vertical "leg" was formed at a little shallower angle...which puts it a bit out of spec, but doesn't cause as problem as long as the slidestop pin location is mid-spec. (The problem doesn't occur on any other pistol here...just the one.) The two issues stacked up to create a badly out-of spec condition that doesn't cause the malfunction every time on any given magazine...and not even very often. Maybe one time in 50. Since Tim goes to the range with me almost every week, I started marking the magazines whenever it would happen...and trying to correct the problem on each. I started noticing that the ones that were marked would do fine for several cycles, and then WHAM...it would happen. It prompted me to really go over it with a fine-toothed comb. When I used a strong light, I finally saw the glitch.

The bend formed a larger radius in the bend than should be there. As the shelf lifted the stop, the radius contacted the bottom rear corner of the lug
and actually pushed it to the right a short distance, so that just a small part of the edge of the shelf was in contact with the lug. Not often...but once in a while...the conditions were just right (or just wrong) and the shelf would climb the lug.

The cure? I cut a small bevel on the offending corner. The clearance gained
kept the radiused corner in the shelf off the lug. The follower doesn't do a sidestep..and everything was hunky-dory.

Yes. I tried other magazines to see if the ones with followers bent closer to 90 degrees would correct the problem. A few did...but most would nudge the lug just enough to move the follower over. Less than the ones involved in the malfunction...but a few still moved it. So...The cure was to modify the lug.

Outstanding diagnosis, lad! Carry on...

 

[1911Tuner]

More

Adding to the problem was the contact causing the slidestop to shift left to the limit of its clearance. Not enough to cause a problem every time...but enough for me to deem it as unreliable and get my thinkin' cap on.

The total movement in follower and stop was...MAYBE..a 64th inch. (.015)
Slide to frame impact was probably the factor that brought it all together,
and provided my final "clew." When the gun was gripped super-tight...the shelf would climb the follower more often. So, we have an instance where "Limp-Wristing" actually made the gun more reliable

 

[Knucklehead2]

I have a cheap mag

I bought for $5.00, and was looking at how much the follower shelf contacts the slidestop, not much probably about .012. I was able to push it over enough to have it jump over but could not see exactly where I would have to relieve.
So I was should I say, guessing? I have some really good prints in pdf. Amazing how much geometry is on the lug of the slidestop. Without the lesson I would have never given it a second thought. Your posts here and elsewhere have really helped myself and others understand how this system works, and for that I thank you.

 

[1911Tuner]

Guess?

Well, you may call it a guess...but the way you homed in on it, I'd have to say it was damn good troubleshootin'.

Just goes to show...It's the little things that getcha.

 

[1911Tuner]

Followup

Ran down to the range early today...around 0700...to see if the mod bore fruit. Happy to report that all 72 of my range mags were tested in the Norinco for last-round slidelock..twice each. Not a single failure.

I call this bug squashed.

 

[Knucklehead2]

Another

happy 1911!

 

[1911Tuner]

Happy

Yep. I'm thinkin' about makin' that little mod a standard part of a reliability tweak. It'll create a little clearance and knock a sharp corner off.

 

[Knucklehead2]

Well I probably

did just that by accident. When I had finished reading one of your posts about the rounds hitting the slidestop, I carefully checked and filed until both hollow points and FMJ's would just clear when I inserted the mag. This area on the slidestop, from what I can see has no function other then clearance. On the drawing I have of the slidestop it is a 25 degree angle. Now, I guess if to much were to be removed even at the correct angle the shelf would get very small.
Like I said, it was by accident removing material to allow the round to clear I eliminated this potential hangup. Better to be lucky then good, sometimes!