Excessive windage
06/06/05
06/09/05

Often caused by the barrel being installed into the upper cockeyed. The barrel will turn as the barrel nut is tightened. Can also be caused by the FSB being mounted crooked on the barrel, the alignment pin, or its notch in the upper, being mis located, or a bent barrel. Sometimes, the front face of the upper, where the barrel seats, isn't square but that is rare. It is normal for the A2 rear sight to sit slightly rotated to the left but just slightly. If the movement of the RSB decreases as the RSB is run up in elevation check that the top most thread on the shaft of the RSB is at the rear of the shaft. If the top most thread is on the front of the shaft the RSB is incorrect.

Excessive elevation
Height of flattop uppers and of corresponding parts and pieces
05/02/05
Is there any difference between a Colt Carry Handle and a Bushmaster?

If using Colt parts be aware that Colt uses a different height FSB on their barrels intended for use on flattops. These are the "F" marked barrels. There are also two different height Picatinny uppers floating around with corresponding detachable carry handles. You may also encounter this problem if you are using a milspec BUIS with a non “F” marked Colt barrel or clone barrels.

Damage to firing pin retaining pin
or
Bolt carrier "catching" or "hanging up"

When used with slotted bolt carriers, hooked hammers can catch the underside of the firing pin, especially if the firing pin has a larger spool on it like those intended for the M16. The hammer will force the pin rearward against the firing pin retaining pin during the battery stroke. With repetition, this will bend the firing pin retaining pin. Sometimes the firing pin retaining pin is a simple, non-hardened, cotter pin. Some of these bend rather quickly. If you hold the trigger to the rear while working the bolt back and forth with the charging handle and the catch disappears you probably have an issue between the hammer and the firing pin. The best fix is to use a shrouded bolt carrier. You can also round the hook on the hammer to prevent it from snagging on the firing pin spool. A short trigger can also cause this by allowing the hammer to sit up too high when cocked.

Testing for a chrome plated bore
Chrome doesn't react with cold blue. Test a shiny white spot near the muzzle and chamber to see if they change color when cold blue is applied. Thoroughly degrease the area beforehand.