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Discussion Starter #1
Here's one for Sherlock Holmes.

During a session yesterday, the portion of the slide stop that engages the mag follower broke off. As a result the slide wouldn't lock back on the last round.

However, it showed up before the last round. When it happened, there were two rounds still in the mag. What happened was that the round in the chamber didn't fire. I pulled the trigger, the hammer dropped normally, but nothing happened.

I ejected the mag, then opened the slide. What came out was the unfired round. The interesting thing about it was that the primer surface was unmarked. No dimple, no breechface marks, nothing unusual. IOW, no indication that the firing pin struck the primer. There were no other distinguishing marks or blemishes on the cartridge.

As I puzzled over this, I decided to lock the slide back manually. As I did so, something "felt funny." I know this doesn't help much, but I can't describe it in any other way. On a hunch, I emptied the mag, closed the slide, inserted the empty mag, and pulled the slide back to see if it would lock in place. It didn't. A quick inspection of the slide stop showed the breakage.

The gun is a Colt M70 MK IV bought new. It is unmodified except for a set of Bo-Mar sights and rubber Pachmeyer grips. The mags are GI issue and the one that came with the gun. There were no problems leading up to the failure, and the gun has not been worked on in any way between this session and the last one, about a month ago. I had already fired 126 rounds before the failure occurred. The only difference between the ammo I used this time and last time is a greater charge: 6.5 g of Unique versus 6.0 g last time. A look at the table in the Lyman reloading manual shows max safe charge for this bullet (SWC 200g hard cast) is 6.8 g. All charges are weighed before they are poured into the case. Yes, I know this is time consuming, but I prefer to do it that way. All rounds are drop tested before they are put in the ammo box.

When I got home, I disassembled the gun for cleaning. I found nothing unusual, and nothing else broken. No unusual marks or scars anywhere.

After cleaning and reassembly, I loaded my dummy squib round (Traditions, 45 ACP) with a piece of masking tape over the primer area, closed the slide and pulled the trigger. The tape was pierced where the firing pin struck it.

Nothing else seems to be wrong with the gun, and I have a new stop in place. What I don't understand is how a broken slide stop could cause the firing failure.

Any ideas?
 

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Interesting...

My only guess would be that the stop (or piece of tip) kept it just far enough out of battery for the FP to not strike?

In theory it shouldn't be possible for the hammer to fall out of battery - but maybe with tolerance stacking - long disconnector slot, slightly short firing pin, etc. it may have happened?

You might try dry firing with the slide slightly out of battery and see if the hammer will fall. Getting the slide to move back a few thousandths at a time might be tricky - maybe use paper shims or a feeler gauge behind the barrel hood.

I dunno...
 

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Howdy Feedramp,

I think JSP is exactly right. As to why the slide stop broke in the first place - it's anybody's guess. Do you have a rough estimate of how many total rounds have been fired through your Series 70 Colt? If it has seen a lot of use, it could be plain old metal fatigue.-TR
 

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Discussion Starter #4
JSP,

"My only guess would be that the stop (or piece of tip) kept it just far enough out of battery for the FP to not strike?"

I agree. Right now, it's all I can think of that makes any sense.

"In theory it shouldn't be possible for the hammer to fall out of battery - but maybe with tolerance stacking - long disconnector slot, slightly short firing pin, etc. it may have happened?"

Agree again. What I can't figure out is why the hammer dropped on a live round without leaving any evidence that the firing pin ever contacted the primer. Maybe your idea about the piece that broke off is what really happened.

So far I haven't been able to get the hammer to fall with the slide out of battery far enough to depress the disconnector. I'll keep trying until I get a chance to take the gun back out, and live fire test it.

TangoRomeo, I think you're right. If you look at the part of the stop where the piece broke off, it looks almost glazed, for want of a more correct term (I'm not a metals expert, so I'm winging it). I've seen metal look like that where metal fatigue was the dominant factor in a breakage.

I stopped counting after 10 K rounds. Admittedly, there have been some gaps in my shooting schedule, but that's what it works out to in round numbers. It's probably more.

What surprised me is that it would happen at all with a Colt factory part. My first 1911 was an old WWII veteran that saw service in the Pacific. I couldn't trace it's complete history, but the owner at the time told me it was issued to him new in 1943. He said it was all original, and that he had never had to replace any of the parts. The barrel was almost shot out, and almmost all of the finish was worn off. The wooden grip panels were almost worn smooth, too.

In spite of all that, it still worked flawlessly every time I used it.
 

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The only other thought that comes to mind about the primer/FP issue is that maybe the slide short stroked when the stop broke and the hammer fell to half-cock ?...but you said you pulled the trigger and it dropped
?????

Had a Colt mag catch break almost immediately on a new Series 80 Commander (a cast part), but the Colt slide stops are known for being good parts. Must have just had a weak spot.
 

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Discussion Starter #6
Originally posted by JSP:
The only other thought that comes to mind about the primer/FP issue is that maybe the slide short stroked when the stop broke and the hammer fell to half-cock ?...but you said you pulled the trigger and it dropped
?????
Yep, and the hammer was at full cock. What tipped me off that there was something wrong was when the hammer dropped on a closed slide, and no bang. When I opened it (mag out first), the unfired round came out.

I've since tried JSP's advice, and the only way I can prevent the hammer from dropping with a trigger pull is to open the slide far enough to depress the disconnector. That measures out to be about 1/16 inch. Anything less than that allows the hammer to drop.

The slide could have been just enough out of battery to allow the hammer to drop, but not hit the FP squarely enough to drive it forward with enough force to cap off the round. Just guessing...I'm still stumped.
 

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Good point on the FP and square strike...some fp's barely extend past the stop plate as it is.

Maybe it was a planetary alignment of all those things - producing the "Murphy's Black Hole" of malfunctions...

Have you tried the dummy and tape with the 1/16" max to see if it's striking? You'd have to jam or hold the slide to keep it from moving forward on the test strike.
 

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Discussion Starter #8
Originally posted by JSP:
Good point on the FP and square strike...some fp's barely extend past the stop plate as it is.

Maybe it was a planetary alignment of all those things - producing the "Murphy's Black Hole" of malfunctions...

Have you tried the dummy and tape with the 1/16" max to see if it's striking? You'd have to jam or hold the slide to keep it from moving forward on the test strike.


Thanks JSP. I'm beginning to think I've got the Murphy's Big Bang of malfunctions, but I'll settle for a balck hole.

The results on the dummy/tape tests is mixed. KInd of like flipping a coin: do it enough, and you'll come up with as many heads as tails.

What happens is just about the same. I haven't come up with a reliable method of holding the slide open a certain amount of displacement and hold it there while I pull the trigger; a feeler gauge between the hood and the breechface is still giving inconsistent results.

The general result seems to be about even; I'm getting about as many pin strikes that break the tape as no strikes at all. There doesn't seem to be any middle ground: I either get a perforated piece of tape, or nothing at all...kind of like a hanging chad or nothing.

The most influence seems to come from the disconnector. I can feel when the slide pushes it down, but the sear spring is doing a good job of making it more of a "on - off" state than anything gradual.

The tentative conclusion at the moment is that, if the disconnector is depressed, the hammer won't normall fall, but if it does, the slide will be displaced enough from battery so that the hammer won't strike the FP hard enough, if at all, to fire the round.

If the slide is still displaced from battery, but the disconnector is fully elevated, the hammer will strike the FP hard enough to fire the round.

I came up with a few ideas on this last night during a slow period on the job. I'll be trying them in the next few days.

I sure won't be shooting for a while. There aren't any shooting ranges where I am, and the only places to shoot anything are out in the wide open spaces.

If you're following the weather, you'll know that it's still winter up here in South Dakota. Denver is supposed to be getting 4 to 8 inches today, and their "foothills" are supposed to be getting up to 18 inches.

Of snow, that is. The wet, heavy kind that turns roads into ice skating rinks.

Heck, I just saw a bull buffalo shopping for a winter coat in the local LL Bean store at the mall.

He found one, too.

NOBODY has taken the snow plow blades off their trucks, yet.

How's the weather where you are?
 

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Snow??

What in the heck is snow?


Weather down here is just perfect. Sunny and springlike.

But that's just to lull us into a false sense of security...at any moment, Hell will burst forth in fury and we'll all be sweatin' like pigs - or even worse, like Rosie O'Donnell trying to get into a pair of panty hose...shudder!

Hope you get it figured out - if I get time I'm gonna see if I can duplicate your problem/test.

JSP

[This message has been edited by JSP (edited 05-04-2001).]
 

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Have you checked to see if anything is interfering with the firing pin motion.

Over time the firing pin spring can have coils break off, so you may have a piece or two that sometimes interferes, and other times does not.

Also, if the firing pin head has mushroomed, it may be coming back far enough for the hammer to strike it sometimes and not coming through the firing pin stop completely other times.

Guy Neill
 

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The same thing happened to a slide stop on a Series 70 Colt Commander. I did not notice anything unusual other than the slide did not lock back on an empty magazine. I probably shot 1000 rounds through the pistol when it happened so I don't think it was due to wear. There are sharp cuts made in the end of the slide stop where it engates the magazine follower that may concentrate stresses there.
 

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Discussion Starter #12
Originally posted by Guy Neill:
Have you checked to see if anything is interfering with the firing pin motion.

Over time the firing pin spring can have coils break off, so you may have a piece or two that sometimes interferes, and other times does not.

Also, if the firing pin head has mushroomed, it may be coming back far enough for the hammer to strike it sometimes and not coming through the firing pin stop completely other times.

Guy Neill

Thanks for the suggestion. The first thing I took apart when I got home was the slide. Nothing unusual...no pieces of metal floating around in any of the cavities. FP spring okay, FP okay, travels freely.

I've repeated the test with the feeler gauge between the hood and the breechface with the same results as before. It comes out about even, and every hammer drop results in a FP strike hard enough to break the tape.

The last couple of days have actually been seasonal enough to allow that big, bright thing up in the sky to come out...scary. Most of the snow has melted, and a lot of the runoff has evaporated, and the ground is hardening, so I may be able to sneak out in the next day or so to live-fire-test the gun.

I'm not gonna go on record about the mud, yet, though. One of the drivers came in last night to start his run with enough dried mud on his pickup to effectively double its weight. If it didn't have a Cummins in it, he may not have made it in.

Still don't know what color it is. Was.

I did come up with an idea to make the distance-out-of-battery more predictable, but I don't have the gear to do it. It involves clamping the gun in a vice or clamp, mounting a depth gauge on the frame with the plunger on the end of the slide, and pushing the slide back with a turnbuckle mounted in another vice facing the first one. Replace one of the loop screws with a cap screw, run it out of the turnbuckle until the cap touches the front end of the slide, calibrate the dial gauge, then turn the screw a certain amount, try the trigger, take a reading, etc.

I don't have all that stuff, so I can't do it myself, but if anybody by chance does, it would be nice if you could try it out for academic curiosity, and let us know what you found.

Just a suggestion.
 

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If you are merely trying to determine the amount of out of battery allowance for the disconnector without firing any ammunition, how about removing the recoil spring? This would allow easier slide movement, so all that would need to be done is move it back a known distance and hold it there, instead of having to hold it against the recoil spring force.

Being a Series 70, there is no firing pin block to worry about, which suggests either the firing pin mechanism, which seems to be okay since you found no sping bits or such, or the hammer/sear. If you lower the hammer slowly, do you feel the half cock notch rub against the sear? If so, perhaps there is occasionally enough rub to rob the hammer of enough momentum to adequately strike the firing pin. This may be caused by a trigger stop adjusted to close to the sear release point.

The only other possibility that comes to mind at present is if the firing pin stop is falling down on one shot so that the firing pin does not come back through it, and then, when you hand cycle the slide, is being pushed back into place sliding across the hammer.

Guy
 

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Discussion Starter #14
Guy,

"...how about removing the recoil spring?"

The idea landed smack between my ear lobes almost at the second I read your post. Thanks Guy, I'll report on the results ASAP.

Meanwhile, I finally got a chance to get out to the firing area. I finished up the rest of the ammo I was working on when the problem came up...176 rounds, including the round that came out when the misfire occurred. No misfires, no jams, no stutters, no stammers, no problems. As far as I can determine, it looks like the gun is back on line. I'm back into reloading mode for the time being. When I get the next batch done, I'll go through it, and we'll see what happens.

The replacement slide stop performed as the original did until it broke: flawlessly. Now all I have to figure out is the misfire problem. Until that happens, or I relegate it to the back burner, any/all suggestions are still warmly welcomed.

Before I forget, thanks to all of you that have contributed thus far. You guys are the reason I decided to participate in this forum.

It's still the best I have found so far, and you are the reason.
 
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