November 11, 2013
By Gus Norcross
The 1911 slide stop is only a $20 part but proper fit and function is critical to the trouble free operation of your 1911. There are several key inspection points we will cover in this article.
1. Pin Diameter: The original G.I. print for the 1911A1 shows the frame hole as .201 inches by .002 inches. I think most commercial frames will be slightly tighter than that spec. Minimum acceptable pin size on the same print is .2005 inches by .002 inches (.1985 inches) and Jerry Kuhnhausen in his classic technical manual on 1911s specifies a minimum diameter of .196 inches. What I do when rebuilding a pistol is to keep the pin diameter within .002 inches of the frame hole. Commercial slide stops are available up to .203 inches in diameter so matching one should be relatively easy. We want a good fit but with freedom of movement so the pin can rotate.
2. Slide Clearance: Kuhnhausen says there should be a minimum of .015-inch clearance between the slide stop and slide and a little more won't hurt. If the stop drags on the slide it could cause premature slide lock. Clearance on the pistol in the photo was about .025 inches.
3. Engagement Corner: The engagement corner of the stop should be only slightly radiused. If it is rounded off from wear or butchering by an idiot with a file, it must be replaced. Refer to the pictures to see a stop ruined by someone who shouldn't have access to tools. The slide stop should fit reasonably well in the slide notch. In some cases the slide notch may have to be dressed up.
4. Lug Protrusion: The slide stop lug protrudes through a window in the frame just far enough so the follower of the magazine can engage it, forcing the slide stop upward locking the slide open. If the lug is too long, it is possible that a bullet can rub against it as the rounds feed up through the magazine and lock the slide open prematurely. If you experience premature slide lock, check the lug face for copper marks indicating bullet contact. This condition is corrected by carefully reducing the lug surface just enough for bullet clearance. Use a stone and go slowly. Power tools may quickly remove too much material from this critical surface.
5. Straightness: Make sure the slide stop lever is not bent. It must fit evenly against the frame. Some cheap cast levers may not be straight out of the package and may exhibit casting lines that interfere with smooth function. When replacing a slide stop, choose a high-quality aftermarket part from a reputable manufacturer.
Measuring the Pin Diameter
Carefully measure the slide stop pin diameter and compare it to the frame hole size. Minimum diameter is .196 inches. The frame hole can be checked with gauge pins.
Checking the Clearance
Check the clearance between the slide stop and slide. Look for .015 by .020 inches minimum. It shouldn't touch. This tolerance can be measured with feeler gauges.
The engagement corner should be only slightly radiused. This one was ruined by over-aggressive polishing. Use hand tools when fitting small pistol parts.
Ruined Engagement Corner
This ruined slide stop will slip right out of the slide notch. The engagement corner is far too rounded. Some can't be trusted with a file, Norcross says.
A Good Fit
The corner of this replacement slide stop is square and it fits the notch in the slide reasonably well. This one will work. Don't get carried away smoothing things.
Note the copper. This slide was locking back prematurely when bullets rubbed the slide stop lug. Gradually reducing the high spots with a stone is the correct fix.