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Intermittent failure to lockup


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Recently had my top end rebuilt by a friend/part time gunsmith. 40 cal 2011.

I have about 1500 rounds through it and getting 1-2/100 rounds that it will not lock up on (not even able to force slide closed). We’ve been trying to figure out why but are both at a loss.

 

Problem has always been there but the first couple practices I chalked it up to “break in”

 

What I checked...

 

Cleaned and removed every bit of carbon.

 

Ammo that fails case gauges and even drops right into the barrel. Even tried dropping into the barrel then closing the slide on it. I even measured everything on the ammo that’s failing and everything is in spec (except for length but barrel is reamed to accept it. And it drops right in)

 

Recoil spring- had a 12. Tried a new 14#. No luck

 

Magazines- good and have new springs.

 

Extractor- tension was loose. Adjusted and problem persists. Put in an aftec from another gun. Still no luck.

 

Since the season is just starting here in PA, I’d really like to try to fix this myself instead of sending it back to him.

 

The only thing I can think of is that the dings (circled in pictures) have something to do with it. Can I knock these down? Other thoughts?948bef11e76bc11b7315756ca53208d6.jpg

 

 

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Your hood, red circled area is catching, the slide occasionally.

Based on the photos,  stone or very lightly file the bbl hood on the contact area you have circled

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16 minutes ago, jcc7x7 said:

Your hood, red circled area is catching, the slide occasionally.

Based on the photos,  stone or very lightly file the bbl hood on the contact area you have circled

Thanks! I'll touch up that area and report back. Do you think I should also touch up that part of the slide that it's hitting?

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Another thing, on a 1911 style pistol with a standard extractor you should never, never put a round in the chamber and close the slide on it. The gun is designed to feed the round up and under the extractor. That is at least part of the cause of your extractor being loose. 

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1 hour ago, Don_B said:

Another thing, on a 1911 style pistol with a standard extractor you should never, never put a round in the chamber and close the slide on it. The gun is designed to feed the round up and under the extractor. That is at least part of the cause of your extractor being loose. 

I'm aware. Only did this once as a test. The extractor was loose before doing this. I adjusted and it was still good after I dropped the slide on the round.

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No luck after knocking that down and cleaning up other rough edges.

I put my old barrel that was fit to my old slide in. It seems to fit fine and all the bad rounds feed without a problem.

If it checks all the boxes for barrel fit I might try it out at the range.


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Have you checked the lower lug dimensions vs slidestop& frame?

 

Without the recoil spring, do you feel any binding or friction of slide? I had this springfield 1911 with their awful coating on it.. 9mm gun. Just the slide and frame were so rough, it would drag and feel like worn out bearings when cycling by hand. Had a similar issue. 1000grit valve compound and some working of the action smoothed out whatever was rough.

 

Is that the proper fix? No. But.. the gun runs reliably now.

 

If lower lug is not properly dimensioned, would it not cause the barrel to randomly bind against the slide? Excess drag of upper lugs.

 

Guess the first thing to check is for additional signs of friction.

 

In so far the magazine itself is not creating a FTF stoppage.

 

 

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Have you checked the lower lug dimensions vs slidestop& frame?
 
Without the recoil spring, do you feel any binding or friction of slide? I had this springfield 1911 with their awful coating on it.. 9mm gun. Just the slide and frame were so rough, it would drag and feel like worn out bearings when cycling by hand. Had a similar issue. 1000grit valve compound and some working of the action smoothed out whatever was rough.
 
Is that the proper fix? No. But.. the gun runs reliably now.
 
If lower lug is not properly dimensioned, would it not cause the barrel to randomly bind against the slide? Excess drag of upper lugs.
 
Guess the first thing to check is for additional signs of friction.
 
In so far the magazine itself is not creating a FTF stoppage.
 
 

I have not. The issue has something to do with the ammo as it only happens 1-2/100 rounds with ammo that is in spec for a hundo case gauge and barrel plunk test. The barrel from my old slide fits the new slide and feeds all the problem ammo without issue.

The problem barrel is just failing to close the final 1/8” on these rounds and it’s a hard stop.


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I have not. The issue has something to do with the ammo as it only happens 1-2/100 rounds with ammo that is in spec for a hundo case gauge and barrel plunk test. The barrel from my old slide fits the new slide and feeds all the problem ammo without issue.

The problem barrel is just failing to close the final 1/8” on these rounds and it’s a hard stop.


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Has the barrel been reamed for longer OAL?

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Has the barrel been reamed for longer OAL?

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Yes. Reamed to accept up to 1.20. Ammo is 1.181-1.188


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It’s fixed! Thanks all for your help. Powder Finger helped me walk through to narrow it down. Had a slightly short chamber that only showed up with a few rounds that had longer brass. Just got back from my buddy’s house and after 6 turns from reamer all the “bad” rounds feed fine.


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Interesting. Any idea how much more deep the chamber is now?
 
Or, any idea how long those problem cases were?
 
Never had this issue before.. however, I must be spending too much time trimming. =/
 
Glad you have it resolved.

I’m not sure. Never pulled the bullets to get an accurate measurement.


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Did you actually measure the chamber before or after to determine if it was/is in spec?

No. Went over to my buddy’s house that fit my top end. Confirmed the problem. Reamed it and is now good to go.


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  • 6 months later...

Have exactly the same set up and problem in my open gun in .38 super/comp. New uppers on old frame. All  Ammo would chamber in my old uppers. But 2/100 will not in new uppers about 3/16”. I removed the extractor and still wont chamber same ammo. Removed slide and barrel and held the ammo by the extractor and it will chamber. Will send it back to my gs. Like the op Id rather fix it myself instead of sending it back. 

If it was chambered short why would the problem ammo correctly gage in the chamber? Why would it chamber when out of the frame? Once, I forced it to chamber w/ a plastic mallet behind the slide. It chambered after a few not so light strikes. Forcibly ejected the round and found no binding marks on the ammo. You would think the chamber would form the brass, fed it again via the mag, again wont chamber completely. 

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Micced 3 chambers in my open guns and heres what i found. All are from barrel hoods. 


Schuemann hybrid: 0.910”

KKM: 0.910”

STI: 0.902”

 

KKM and STI were made by same gs. 

STI barrel is the one in the gun that fails to lock up about 2 in 100 rnds. Considering .38super is a straight walled cartridge, is .008” enough to cause OOB by 3/16-1/8”?

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6 hours ago, BoyGlock said:

Micced 3 chambers in my open guns and heres what i found. All are from barrel hoods. 


Schuemann hybrid: 0.910”

KKM: 0.910”

STI: 0.902”

 

KKM and STI were made by same gs. 

STI barrel is the one in the gun that fails to lock up about 2 in 100 rnds. Considering .38super is a straight walled cartridge, is .008” enough to cause OOB by 3/16-1/8”?

 

Absolutely. If you try to put a size 9 1/2 foot in a size 5 shoe, something has to give. But whatever the OAL of the round you choose, regardless of HP, FP, RN, it has to fit said barrel.

 

It has to fit into the chamber without the bullet being seated too long for your particular chamber and in some way hitting the lande. .008" oversized (in your case per trials) is just enough to keep the barrel from locking up into full battery, which means the end of the round is stuck up against the breach face, stopping full lock up. Shorten the OAL. Science by Thomas Dolby.

Edited by Lastcat
spelling...argh! F#ck me
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6 hours ago, BoyGlock said:

Micced 3 chambers in my open guns and heres what i found. All are from barrel hoods. 


Schuemann hybrid: 0.910”

KKM: 0.910”

STI: 0.902”

 

KKM and STI were made by same gs. 

STI barrel is the one in the gun that fails to lock up about 2 in 100 rnds. Considering .38super is a straight walled cartridge, is .008” enough to cause OOB by 3/16-1/8”?

Yes. But also no. There are two things at play here. The chamber and the throat. The chamber depth should be cut to SAAMI spec and no deeper. The chamber reamer has a throat cutting section on it but will only cut the throat to normal spec for commerical ammo. Think winchester white box, blazer, ect.  Depending on how long you load your ammo the bullet itself is probably hitting the rifling of the barrel and not allowing the case to go fully in the chamber. To fix thing you need a thoating reamer. It will cut the throat and not the chamber. 

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When i chamber gage my reloads that wont feed, the rims were a bit pronounced over the barrel hood. This could really prevent lock up in the lugs. I understand now the geometry of the round feeding at an angle and w/c wont seat flush w/ the barrel hood. 
Thanks guys

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