Some basic tips for assembling lower receivers on your AR rifle. Assembling a lower receiver is not really that big a deal, it will, however, go much smoother if you make a few tools to help you along.
The first thing that makes assembly easier is some way of holding the receiver while you are working on it. We sell an excellent tool for this, called a lower receiver vise block, but an old junk magazine with some wood stuffed inside it will work if you clamp it in something (a vise). The military manual has blueprints for some extra tools in the back, these can come in handy. Some of those tools we use here.
Some other tools we use here are called slave punches. A slave punch is just a punch with a hole in the end to hold a roll pin and get it started in the hole it's supposed to go into. Brownell's (515-623-4000) sells these, or they are easy to make. We use a different slave punch for every roll pin in the rifle. Some pins are the same size, but as they go in different places, we use a different punch for each one, one with an end specially shaped so as not to leave a mark on the finish in that area. We make the ones we use here out of stainless round stock, but they can be made out of just about anything. These are what let us assemble without leaving marks all over the place.
The military manual shows all the assembly and disassembly necessary to work on these rifles in detail with illustrations. It is important to update your manual every few years, as the new changes keep coming. The new A-2 manual, for instance, has the complete section for the M-4 carbine, covering the tele-stock assembly and specific parts list. They keep changing things too, like the setting of the elevation dial on the A-2 rear sight.
Some common problems with assembly are forgetting to insert the disconnector spring, placing the tails of the hammer spring under instead of over the trigger pin, losing the takedown pin detents, and putting the bolt catch spring in the disconnector spring pocket. These are all very simple mistakes, but they will cause major malfunctions down the road.
Fortunately, they are easy to fix, if you are looking for them. Installing the hammer spring backwards is another popular mistake. Not a problem, as it's easily corrected. Again, the manual or the assembly video will show you the mistake. Losing the buffer retainer and spring is another popular one. If you are installing or removing the stock assembly (or receiver extension), you have to hold on to that little sucker, or it will fly! Always support the ears of the trigger guard when installing Roll Pin with a piece of wood to prevent breaking off the ear.