Pre Series 70 Colt odd problem

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John Travis

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The year was 1983...I think...and a guy walked in with a Colt Government Model, circa 1970. Fairly high mileage gun with a lot of vertical slop frame to slide. Lifting the front of the slide made a good bit of the recoil spring visible. Sloppy.

Owner wanted a little tuneup and a new barrel. The rails would require a beatdown to get rid of the vertical slack and I ordered a new factory Colt barrel for it. He didn't want to drop a lot of cash on it.

So, I beat on the frame rails with a hammer and swaging punches until I got it where I wanted it. Oddly, the side-to-side play was minimal, but I lowered the slide on the frame a good bit.

Okay. Got it all refitted and smoothed up...barrel fit was good...put it together, and...

When I pulled the trigger, the hammer wouldn't fall. Because I hadn't replaced any of the fire control group, I was a little mystified. Took it apart and had a look. Nada. Zip. Put it back together, and the hammer wouldn't fall. The trigger met with a little resistance from the sear, but the sear wouldn't trip. Just slipped on past it.

I disassembled and reassembled it without the grip safety so I could get an eyeball on everything...and I saw it.

Aha. That makes sense.

The fix took about five minutes.

Owner was happy. He said the gun wasn't that tight when it was new.

Clue: It's the little things.

Noodles in gear...

Go!
 
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John Travis said:
Clue: It's the little things.
Click to expand...
Disconnector and sear, that be them little thangs...

But, how come it worked before, when the slide was higher?

John Travis said:
The trigger met with a little resistance from the sear, but the sear wouldn't trip. Just slipped on past it.
Click to expand...
Sear spring middle leaf too long?
 
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Me. said:
My first thought was disconnector not moving smoothly up and down through the frame.
Click to expand...

Smoothly enough.

Me. said:
Then I looked for a picture and thought.... is the hammer hanging up on the newly-beat-down frame?
Click to expand...

Nah.

MacEntyre said:
But, how come it worked before, when the slide was higher?
Click to expand...

Indeed. And why does it NOT work with the slide lower?

MacEntyre said:
Disconnector and sear, that be them little thangs...
Click to expand...

This was littler than them thangs.
 
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littler, eh... ?

I wonder if it was the disconnector hole?
Might have been worn itself, as the slide fit got looser.
Lowered slide, moved the hole down, but not along it's axis, disconnector stuck.
Could that be it?
 
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Disconnector not moving up because the divot in the slide is not deep enough?
That divot, or hole, moved down but not centered on the disconnector?
 
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John Travis said:
Yes!

But...why?
Click to expand...


Three little bitty things combined in a classic tolerance stacking to create this glitch. A condition where three related pieces of the puzzle were within spec...barely...but together threw the assembly out of spec.


First, I'd noticed that before the work, the slide sat just a few thousandths forward on the frame so that the rear of the slide and frame weren't aligned. It was just enough to be noticeable without being a problem. This is present fairly often. The cause was that the barrel lower lug feet were a little thin. Within spec, but just.

Second, the disconnect slot in the slide was just a few thousandths short in the front. Again, within spec, but just.

Third, the disconnect spade was a few thousandths short top to bottom.

Originally...according to the owner...the slide had a little vertical play when the gun was new. Nothing unusual there. Most Colts of that era had a little vertical and sideplay on the order of about .005 inch. Barely discernable. When I brought the frame rails down, I removed all vertical play, and in so doing probably lowered the slide an additional .003 inch It makes the gun smoother and maximizes vertical barrel lug engagement.

The combination of the three tolerance stacks and bringing the slide lower on the frame resulted in the disconnect being unable to fully reset and provide enough overlap with the sear feet to stay engaged...and when I pulled the trigger, the pressure forced the disconnect back into the disconnected position.

I could feel the resistance from the sear, and then I could feel the disconnect lose contact the same way it does when a weak or overtweaked sear spring can't keep the disconnect in position. If the disconnect spade had been mid-spec or so, the hammer probably would have fallen to half cock.

The fix was a simple matter of replacing the disconnect and using a correctly sized keyway cutter in a universal vertical mill to lengthen the slot.

Okay. 10 minute fix counting setup time and not counting detective work.

.003 inch here and .oo5 inch there and .010 inch in another place. Little bitty, teeny tiny thangs can mean the difference between a functional machine and a paperweight.
 
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