Originally Posted by Dillinger
Plunger tubes just don't "Fly Off" without reason.
They do if they are not staked!
MidwayUSA - Strobel Plunger Tube Staking Tool 1911
You need a staking tool to do it right or you can chamfer the inside and peen the tube to the receiver.
This is an excellent handbook, U.S. MARINE CORPS TECHNICAL MANUAL TM 00526A-24&P/2 ORGANIZATIONAL AND INTERMEDIATE
MAINTENANCE MANUAL INCLUDING REPAIR PARTS LIST PISTOL, CALIBER .45, MEU(SOC) (1005-01-370-7353)
see page 6-38
From Small Arms Essay Looking Down the Barrel of a Gun
FLAWS IN THE BASIC DESIGN AND A PROPENSITY TOWARD SMALL PARTS BREAKAGE (Well worth the read!)
THE PLUNGER TUBE:
The plunger tube that runs between the slide stop and thumb safety is a notorious weak spot in the basic 1911 design. This tube contains two little plungers and a spring, the power of which serves both to hold the slide stop in the down position until operated by the follower of the empty magazine as well as to hold the thumb safety lever in the safe or fire position. This is a high-stress area of the gun; every time you flip your thumb safety on or off, you apply force to the plunger tube. Unfortunately, the plunger tube is held to the side of the gun only by two small studs that pass through holes in the frame. It is not at all unusual for one of these studs (almost invariably the rear one) to snap off. I've had this happen myself while shooting, and I've seen it happen to other shooters. When this happens, your thumb-safety lever will wind up in a half-on/half-off position. In an emergency, it would be possible to physically hold the safety lever down in the fire position and still shoot the piece. However, for all practical purposes, the gun is disabled until the plunger tube is replaced.
There's really nothing you can do about this problem except to keep a close eye on your gun's plunger tube for signs of looseness. Some folks say that if your plunger tube is loose, you should simply have it restaked. I don't know about that. If the plunger tube has been loose for any amount of time, that rear stud has probably been abused enough that I'd probably feel better myself simply replacing the tube with a new part.