The M1911 Colt .45 automatic pistol was, as the name implies, first introduced into service with the U.S. armed forces in 1911. It remained in use until well into the 1980s. Between the official versions of this venerable handgun and its various copies, millions of M1911s have been made over the years, making it a widely available handgun. Some of these guns come disassembled, while any cleaning or repair requires at least partial disassembly. Therefore being able to assemble the gun is a vital part of owning it.
Drop the trigger, which is a single, solid piece of metal, through the slot in the back of the handle so it fits into the trigger guard.
Slide the magazine-catch button into position, in the slot just behind the trigger. If it does not fit, that means you put it in backwards. Once the button is in place, tighten the screw on the magazine catch to fasten it into place.
Fit the disconnector inside the middle of the sear. These are two small, curved metal parts. The end of the disconnector will stick out like a pin. Fit that pin-like end into a rounded hole in the back of the gun, between the slot where you fitted the trigger and the place where the hammer will eventually go. There is a channel running through the top and back part of the pistol, with a hole on either side. If you have placed the sear and disconnector properly, the hole middle of the sear will fit into this channel, enabling you to push the sear pin straight through. Tighten the sear pin with a screwdriver.
Push the hammer into place on the back of the gun, just above where you were working with the sear and disconnector in Step 3. The middle part of the hammer is a squared cog with a hole running through it. Align that with the matching holes in the back of the gun, and slide the hammer pin through.
Flip up the hammer strut, a long metal bar attached to the hammer. With the pin in place, it should flip up smoothly. Set the leaf spring, a metal panel with three separated prong-like leaves, into the back of the gun handle with the leaves pointing up. Flip the hammer strut back down and check the hammer to see if it works. If the hammer can be pulled back to half-cock and full-cock, but will not release without pulling the trigger, the leaf spring is seated correctly.
Set the grip safety, the part of the handle that sits over the space between your thumb and the rest of your hand, into place in the back of the gun and underneath the hammer. Then slide the mainspring housing onto the back of the handle, until it meets the grip safety.
Place the mainspring pin into the hole in the lower back corner of the handle. Tap the pin all the way into that channel through the handle with a rubber mallet. The pin will snap into place.
Slide the slide-release plunge into the tube on the left side of the pistol frame. Then drop the spring into the tube, and finally the safety plunger.
Drop the pin on the slide-lock safety into the sole, remaining hole on the top and back of the left side of the gun, between where you pinned the sear and the hammer. Use a screwdriver to fully depress the safety plunger, pull the hammer back to full-cock, and then move the slide-lock safety into a position where it continues to hold down the safety plunger. Pull back the screwdriver. This will lock it into place. The grip safety is the only moving part of the safety assembly. Check the safety by pulling the trigger. If you cannot pull the trigger without also squeezing the grip safety on the back of the gun handle, the safety assembly works.
Set the slide onto the table so the muzzle end is pointing down. Hold the extractor rod so the notch at the bottom faces left. Drop the extractor rod into the channel on the right side of the slide.
Slide the firing pin into the firing-pin spring. Drop these parts into the center channel of the slide. The back of the pin will stick out of the channel. Push the pin down onto the spring with a screwdriver and slide the firing-pin stop into the grooves in the back of the slide until the hole in the middle of the firing-pin stop is directly above the firing pin. When you remove the screwdriver and release the pin, it should spring into place and lock the firing-pin stop into position.
Push the barrel into the front of the slide, pressing down until the locking lugs engage.
Set the slide on the table so the bottom of the slide is facing up. Take the receiver-spring guide rod, which looks like a hollow bolt with a rounded edge. Place the rounded edge against the barrel and slide it into place in the front of the gun, so the hollow tube of the guide rod resembles a second gun barrel, sitting next to the actual barrel you installed in Step 12.
Install the slide into the top of the pistol frame, literally by sliding it into place. In the center of the frame there is a hole running through to the other side of the pistol. Make sure the slide is in position and there is a clear channel running through this hole, and drop the slide-stop pin into it. Pull the slide back so that a tiny notch on the underside of the slide is aligned with another hole in the side of the gun, set in front of the tube where you assembled the parts for the safety in Step 8. Push the slide stop up and into this notch, then press down on the slide-stop pin to finish locking it into place. Check the slide. If it has only a limited range of motion, and you cannot get it off the gun, the slide stop is properly installed.
Install the bushing. This is a part that fits over the front end of the barrel. Push down on the bushing so the slide goes back as you do. Then release the slide to click the bushing onto the barrel. Turn the notches on the bushing to point to the left side of the pistol.
Push the receiver spring into the hollow tube of the guide rod, through the front of the gun. Place the spring plug over the top of the pistol, push the plug all the way down into the gun, and then turn the notches of the bushing down until the cover the plug and lock it into place.
Set the grips onto the handle and fasten them with screws.
The M1911 was made so that no tools would be necessary to disassemble and reassemble the gun. Strictly speaking, you can use the gun's own parts to turn all the screws and fit all the pins. Having a screwdriver and mallet makes it easier, however.
All of the parts on the M1911 were made so that they fit only in the right place and in the right way. A given pin, for example, will only fit in the slot designed for it and no other. If the part doesn't fit, try turning it. You might have it misaligned. If it still doesn't fit, you are using the wrong part.