Let's get one thing straight from the get-go. I love everything about this rifle. I am so sick of people badmouthing this fine weapon that I won't even respond to the sanctimonious criticisms we all hear. For the hunting I do in rural Iowa, it is the perfect rifle. If I were fighting commies or Al Qaeda I would rather have an M-14. But the only long range enemies I shoot at are ground dwelling varmints commonly referred to as prairie dogs and my AR is just the ticket for them. If I could only have one self-loading rifle--not merely a theoretical exercise given the current administration--and felt certain I would never leave rural Iowa, I'd take my AR. Now, if I had reason to believe I might find myself in Alaska, I might opt for an M-14 (M-1A).
Right out of the box the AR-15 rifle is fine. Old boys around my neck of the woods have been sawing off carrying handles, free floating the barrels and low-mounting scopes on their beloved ARs for years. These guys use AR-15s exclusively for coyote/fox hunting and this configuration makes a lot of sense for predator hunting. But I personally like the carrying handle and I can't say I've ever missed a shot because my scope was mounted high.
Also, I've never seen a properly maintained AR that wasn't anything but absolutely reliable. So please take the smoothing I'm going to describe for what it is--tweaking. I have some friends who I consider extremist audiophiles. These fellas spend $200 on speaker wire. They say if you turn the cable around and swap ends from the amps to the speakers it makes a sonic difference. That, my friends, is tweaking. I'm sure they feel the same way about the procedures I'm going to describe.
I've never seen obnoxious tool marks on the feed ramps of an AR. But polishing without abrasives can't hurt. That's a good place to start. Ensure your weapon is unloaded and field strip it. Wipe the chamber and all parts in the bolt carrier assembly free of oil. Leaving the upper and lower receivers separated observe the feed ramps on at the base of the chamber. Put a pointed felt tip on the proper Dremel mandrel and sparingly apply Simichrome on the feed ramps. There is no reason to use sandpaper on the feed ramps so don't. We want to tweak, not alter. Polish the feed ramps with the Simichrome and move on to jeweler's rouge. Don't spend a lot of time here, just polish to you can see the ramps start to glaze. This reduces friction for those incoming bullet noses.
Next, examine the rails on the bolt carrier. You should see areas on the rails at the base and to the side of the bolt carrier key that appear worn and or shiny. These are friction areas. Smoothing here will make everything work a little easier but again we just want to tweak. With the 600-grit paper go to work on any gouges and dings in these worn areas. Don't spend a lot of time with the sandpaper because you don't want to remove much metal. Go on to the Simichrome and rouge and get those edges to shine. Your bolt carrier should move in and out of the receiver as if suspended on silicon bearings.
Turn over the bolt carrier and examine the bottom. This high friction area contacts the top of the hammer during cycling. Go to work with sandpaper and lessen any marks, dings or gouges. Graduate to Simichrome and rouge and smooth the whole surface until it shines. Don't worry about a few marks. Just better the worst of them.
Take a look at the bolt cam pin. This pin is also a high friction area. You'll notice several distinct wear patterns on this little pin. Start with the Simichrome polish and go on to the rouge. Make the wear marks sparkle. Polish the back of the bolt behind the gas rings with Simichrome and rouge. This part moves in and out of the rear of the bolt carrier during cycling and polishing in this area reduces friction.
The top of the hammer face, the surface that actually strikes the firing pin, is in contact with the bottom of the bolt carrier during cycling. Lightly sand here with the 600-grit sandpaper, paying particular attention to any tool marks at the rear of the hammer face and continue polishing with Simichrome and jeweler's rouge.
Also the insides of AR-15 receivers have a special coating. Do not polish, sand or otherwise scrape the interior surfaces of the AR's upper receiver. Limit polishing and tweaking to steel parts only. For the tweaking I'm about to describe, you will need a Dremel tool and felt wheels, 600-grit sandpaper, Simichrome paste, jeweler's rouge, a medium/fine steel file and a touch-up-black pen.
As I mentioned earlier, military-style rifles are not known for their trigger pulls. Usually they are gritty and can benefit by taking the roughness out of the hammer/trigger contact area. Please don't even think about using sandpaper here. You can ruin your rifle if you use abrasives on the hammer/trigger contact area. Just polish this area with Simichrome and rouge.
With your thumb on the top of the hammer, pull the trigger and ease the hammer to rest against the back of the magazine well. Look down into the lower receiver and observe how the hammer assembly goes together. Notice that the two arms of the hammer spring ride atop the trigger pivot pin. With your thumb on the hammer push the hammer pivot pin out to one side with a small nail or similar tool and remove the hammer. Pay attention to how the hammer pivot pin comes out and put it back in the same way.
Wipe the hammer/trigger contact area on the hammer free of oil. Polish the contact area with Simichrome and then rouge. Spend some time here and get the contact edge/corner as polished as possible. Don't bury the Dremel felt tip into the metal, keep rpm up by letting the Dremel tool do the work. This area should be glass smooth. Then smooth the trigger/hammer contact edge on the trigger assembly. You should be able to polish this edge with the trigger still in place. Wipe these area free of polish and oil liberally. Reassemble in reverse order of disassembly. Do not use force to seat the pivot pin. You should be able to do this with finger pressure if everything is aligned properly. Check operation to ensure everything is reassembled properly but do not let the hammer smack into the back of the magazine well.
There is no shortage of other improvements AR owners can make at minimal cost. For about $20 I installed a Trijicon tritium night sight front post. Granted, this is beneficial only at close range during low light conditions but I have occasionally stumbled across Mr. Coyote in that scenario. If you generally rely on your iron sights, try to file the front post for more precise shooting. With the fine side of the file, take an equal number of strokes to both the right and left sides of the front post. By removing a small amount of metal you can get a more precise sight picture. Touch up the exposed metal with a swipe or two from the touch-up black pen.
If you really want to squeeze precision from your AR consider installation of an aluminum forend that allows your barrel to free float. This reduces torsional effects presented when using a taunt sling and when resting the forend on sandbags or a bipod. Eagle Arms, Box 457, Coal Valley, IL (309) 799-5619 offers everything from knurled aluminum forends to match sights and trigger assemblies to complete rifles. If you really want to go all out, let technician Randy Farrell at Eagle Arms install a match barrel or 4.5 pound, clean-break-trigger group and transform your run-of-the-mill AR into a tack hammer. Finally, tweaking your AR-15 might be for the fella that has a little too much time on his hands. Then again, I can't think of a better way to invest some free time.