1911 won't lock open

[Col. Harrumph]

Beats me: my 1918 pistol just won't lock open on the last shot, no matter what magazine I shove up its butt. Those same mags lock my other 1911's open reliably (I own 5, I guess I like 1911s). I'd post a pic but you already know what they look like. Oh I should add that the miscreant pistol has no problem locking open when I rack the slide on an empty magazine; it's just on the last shot that it fails. Maybe it's some kind of timing issue?

Oh hell, OK:

 

[NIGHTLORD40K]

Rounded off slide stop?

Or, perhaps its short stroking a bit. Any extra-heavy springs or buffers involved?

 

[1KPerDay]

What ammo?

 

[CapnMac]

Pull the problem slide pin out. Compare it to a known good one--a magnifying glass is your friend here.
As a guess, one of the various important surfaces has worn away a bit.

 

[Jeff62]

I had the same issue with well used/much loved Colt series 70. I changed out the slide stop and had no further issues.
I hope that simple fix works for you.

 

[ontarget]

I was also going to ask about ammo as it sounds like it might be short stroking. If it locks back when you rack it with an empty mag in place.

 

[Col. Harrumph]

Yeah I was thinking about the slide stop. Which surface?

(It's not the ammo, it happens with my reloads and with WWB.)

 

[hutch51]

Similiar problem on a Rock Island. The other three 1911s had no problems with the magazines. Colt slide stop fixed it. Got the part from Midway if I remember correctly.

 

[Tallball]

Yeah, my 9mm 1911 was doing that recently. I replaced the slide stop pin with one from Midway ($20-something?) and it's fine now.

 

[Steve in Allentown]

1918 slides weren't spot hardened around the slide stop notch were they?

You might take a look at the notch to see if it's been deformed.

 

[CapnMac]

Which surface?

First place I'd look would be the spring pin detent surface.
Might be dimpled (or warn) enough that the stop won't pop up enough to work under recoil; but will under the less-rapid hand-working of a slide.

The 1.5th place I'd eyeball would be the plunger spring pressure. In recoil, inertia is moving everything is wanting to move backwards not forwards, and there might not be enough "oomph" on the pin to push it up into engagement.

Second place would be the surface that catches the mag follower.

Third place to look is the contact surface where the stop engages the slide. One or the other might be "peened" just enough to matter.

Buying a new slide stop (and storing the old, as it's off an 1918) might be all you need.

 

[Col. Harrumph]

Thanks Steve and Cap'n, now I have some knowledge I didn't have yesterday. THR rocks and you guys are why!

 

[2ndtimer]

https://www.midwayusa.com/product/100573031?pid=841313