Colt MK IV Series 80 last shot hold-open

R

Roamin_Wade

Moderator
My Colt Combat Elite, bought in 1996 by me from the store that I now work at, does this little thing that I’d like to get some opinions and feedback about. It happens when it’s cold sometimes but happens regularly while it’s heated up. Prior to the description of the technical malfunction I’d like to say that I’m inclined to keep it this way as opposed to fixing it. What it’s doing is upon last round ejection and hold-open, when I bump the next magazine into the battery position, the bump upwards causes the slide to jump off the knife edge that is holding it open and loads the first round without ever having to apply pressure to the slide release. It’s almost like it is worn out perfectly, for lack of a better term. What I wonder about is what may happen if it wears further or maybe is there an aspect to this dynamic that I’m not realizing and that I need to have it corrected post-haste. Thoughts?
 
Roamin_Wade said:
What it’s doing is upon last round ejection and hold-open, when I bump the next magazine into the battery position, the bump upwards causes the slide to jump off the knife edge that is holding it open and loads the first round without ever having to apply pressure to the slide release.
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It will eventually get to the point where the slide won't lock open after the last round is fired. It could be a few things that are causing this to happen. Here are the more common ones:

  1. One is that the slide stop is not fully engaging the notch in the slide. A close up picture of the notch with the slide stop manually pushed as high as possible into it would be extremely useful.

    If the top of the slide stop tab doesn't contact the top of the slide notch, some metal will have to filed away in one or two places on the slide stop to allow full engagement.

    This is the very first thing to check. If it doesn't do as I described, this is where the problem is and there's no need to continue.


    Stuff like this is always clearer with pictures. The one below shows the area of the slide and slide stop that we're talking about.

    aakx7Sx.gif




    The next one shows the rear of the slide stop. The pink area is where the side of slide fits into when the slide stop is pushed up to engage the notch in the slide. Sometimes the bottom of this area needs to be deepened to allow the slide stop to rise higher into the slide notch.

    XReCpbD.jpg




    The next one is a view of the slide stop from above. The yellow area is the same area as the pink area in the picture above.

    Xqdt5FC.jpg



  2. If there is a polymer buffer on the recoil spring guide rod, remove it. It reduces the amount of rearward travel of the slide and may be affecting the ability of the slide stop to engage the notch.

  3. Remove the slide. Put the slide stop back into the frame. Slowly insert an empty magazine and observe how it engages the lug on the slide stop and whether it moves the slide stop with authority all the way up. If it doesn't the mag spring may be too weak and can be easily replaced.
 
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Roger that Steve. After looking at it per your suggestions I see it being a little rounded off on both knife edges but also in combination with a weaker spring in mag. I'll get home and change mags out and see if that does it. I don't know how to post pics in here. I've been told but my phone takes larger computer space pics than this site will accept. Thanks...
 
Be advised, a correctly fit slide stop tab will fill the entire slide notch. You need lots of contact between the two. This helps to prevent peening of the notch. Another tidbit is that the outboard edge of the slide stop tab should NOT bear the full load of holding the slide open as this will lead to peening of the notch. The load should either be spread across the entire surface of the tab or more to the inboard edge.

If the slide notch is sloped toward the outboard edge of the slide, I would take it to a real 1911 'smith and have him correct the notch.
 
Do check closely to be certain that its not YOU bumping the slide stop during a reload, without realizing it. This happens more often than you might think.

Slamming the mag home is dramatic, looks good on TV, but its a poor way to treat the mechanism, and can result in just enough of a bump to the gun that trips the slide stop with your hand, without you being consciously aware you are doing it. We had a fellow on here not too long ago with a similar problem, and it turned out when he changed the way he was doing his reloads, the problem went away.

Yes, the gun could be worn, and could need repair. Or it could be the technique used. It could even be both in combination. See if you can figure out which it is, because fixing the wrong one won't cure the problem.

Good Luck!
 
I have a Beretta 84 that I bought used. It let the slide go occasionally when I first bought it, and progressed fairly rapidly to not holding the slide open at all. The aft end of the slide catch was badly rounded off, and a replacement part has not been available. I filed the back edge square, so it now holds open reliably a millimeter or so forward of where it should. I'll replace the part when it is available, but it is functioning nicely for now.
 
My SM ACE .22 wore out the notch and I had it welded and remachined.

My S&W Plastic M&P reliably "autoforwards" which is a competitive advantage in IDPA.
 
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