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Old January 20, 2019, 01:58 PM   #1
Steve in Allentown,
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1911 slide failure to lock open on an empty magazine - new cause

This subject has been addressed many times and solutions include such things as replacing the magazine spring, bending the engagement tab on the follower outward, replacing the slide stop, using hotter ammo, replacing the recoil spring with a lighter one, and others.

Today I discovered a new-to-me reason for this kind of malfunction.

I had multiple failures-to-lock-open with three specific magazines. I chalked it up to cold weather and/or a weak powder charge. But this just didn't make sense to me since this pistol has had thousands of rounds through it with many magazine brands and has always run 100%.

When I got home I disassembled the three problem mags and remembered this was their first trip to the range. I put the followers back in and did my usual teeter totter test which they all passed. Then I put the mag springs back in with just enough tension to provide some resistance to the follower. I pushed each follower down and slowly let the springs push them back up and each follower got stuck just before coming all the way up into contact with the feedlips.

After a few more diagnosics I determined there was a burr left over from the manufacturing process on the inside surface of each mag tube in just the right place to prevent the follower from coming into contact with the slide stop lobe. This did not affect the feeding of the last round in the mags.

The fix was removing the burrs. Another trip to the range and the mags ran faultlessly.

The arrows in the pictures below point to the spot where the burrs occurred (inside the mag body).






Here's some more detail to show where the burr occurred and how it interacted with the follower.

"A" and "B" in the picture below are pointing at different areas of the tab on the mag follower that makes contact with the slide stop lobe to push it up after the last round in the magazine is sent down range.

"A" indicates the very top surface of that tab. This is what actually contacts the underside of the slide stop lobe. If you look very carefully, you can see this surface looks a little different than the rest of the follower. That's because the follower wasn't cleaned after shooting and the powder residue has been worn away in that spot because of repeated contact with the slide stop lobe. This picture was taken after I'd gotten rid of the burr and the follower was now doing its job of holding the slide open.

"B" indicates the very edge of the tab where it had been running into the burr. Once again, a close examination will reveal a very small area where the bluing had been worn away by the burr.




"C" in the picture below shows the exact spot where the burr and the follower met. When this happened the follower would stick which meant the follower tab couldn't push the slide stop up to engage the slide. Note how the follower is not fully up against the feedlips.

The follower had not been stopped by the burr until after the last round had been chambered. At that time the follower rose up in the tube but was still being slightly depressed by the disconnector rail. When the slide moved rearward and the disconnector rail was no longer depressing the follower, the follower moved up enough to hit the burr which stopped it in the position shown in the picture.

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Old January 20, 2019, 02:18 PM   #2
CedarGrove357
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Very nice!! Thank you for the detailed diagnosis and repair. +1 subby!

Sent from my SM-G955U using Tapatalk
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Old January 20, 2019, 06:30 PM   #3
mete
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Yup a small burr , sticking out no more than 0.001" can really raise hell !
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Old January 20, 2019, 11:36 PM   #4
RickB
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I just checked seven mags sharing the same follower design, presumably from the same manufacturer, and none has a burr there.

I had a couple of instances of the slide running home without having activated the slide release, thinking maybe "the burr" was preventing complete slide stop/release engagement in the slide, but it must be something else.
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Old January 21, 2019, 01:38 PM   #5
4V50 Gary
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Good post.
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Old January 21, 2019, 04:41 PM   #6
Steve in Allentown,
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Quote:
Originally Posted by RickB View Post
I just checked seven mags sharing the same follower design, presumably from the same manufacturer, and none has a burr there.
Over the course of the past year or so I've purchased somewhere around two dozen of these magazines mostly from Top Gun Supply and some from Ed Brown. Of these, six had the burr and these all came from EB. However, not all the EB mags had the burr. I suspect I was the lucky guy who managed to get all the ones that QC didn't catch at the manufacturer. No big deal.

These mags are my absolute go-to mags as a result of an exhaustive feeding test I ran a while ago during which I tested every combination of every size and model of 1911 I had on hand, every factory loaded ammo both HP and FMJ from every manufacturer I had on hand, my own handloads, and every magazine from every manufacturer I had on hand. This resulted in literally thousands of rounds being cycled through these mags and pistols over a three day period and a very sore thumb.

These mags proved to be the smoothest feeding of all magazines across every pistol and ammunition combination. Other very well known and highly rated magazines from Tripp, Wilson, CMC, and MecGar did not feed nearly as smoothly. In many instances the feeding cycle with these other mags was quite clunky and hesitant. I'm not saying they didn't feed (in some cases they didn't) just that they were not as smooth.

Quote:
I had a couple of instances of the slide running home without having activated the slide release, thinking maybe "the burr" was preventing complete slide stop/release engagement in the slide, but it must be something else.
A topic covering all the possible causes of a failure-to-lock-open deserves a thread of its own.
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Old January 25, 2019, 02:44 PM   #7
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Quote:
I had a couple of instances of the slide running home without having activated the slide release, thinking maybe "the burr" was preventing complete slide stop/release engagement in the slide, but it must be something else.
I had that problem. It went back to Colt a couple of times, each time returned to me with the assurance "problem resolved." It wasn't resolved.

Finally, I took the slide stop and used a dremel tool to increase the depth of the little indentation in order to provide a more secure stop for the plunger. It's been ok since then.

(I just knocked on wood.)
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