Combinations of barrels and buttstocksAs long as you keep the short (collapsible stock style) buffer spring with the short buffer in the short lower receiver extension and the long (rifle style) buffer spring with the long buffer in the long lower receiver extension it doesn't matter what barrel length you use.
Collapsible stock spring length range:
10 1/16"-11 1/4"
Rifle stock spring length range:
11 3/4"-13 1/2"
Do not stretch the buffer spring, or any spring, to increase the length. Do not clip off coils to gain function.
Pictures of buffers courtesy of BiggerhammerIf your buffer is plastic and filled with birdshot or similar material throw it away and buy a proper buffer. You should be able to hear the weights slide in a proper buffer.
Free Float HandguardsAssemble your own ARDamage to buffer or buffer retainerThe buffer should not touch the buffer retainer when the rifle is assembled. The buffer only touches the retainer when the upper is removed from the lower. When the rifle is assembled the rear of the carrier pushes the buffer away from the buffer retainer. You should be able to see, hear, and feel this when you close the upper onto the lower. If there are dents in the face of the buffer that correspond to the buffer retainer either the pin hole for the retainer is mis located, the carrier is short, the barrel sits too far forward in the upper, or the upper sits too far forward on the lower. The rear of the carrier should be flush or slightly above the rear of the upper. The rear of the barrel extension should be flush with the inside lip of the upper or recessed no more than ~ 0.012”.
A rough spot on the rear of the carrier most often causes wear on the face of the buffer. The most likely place for the rough spot is at the rear of the key way cut in the bottom of the carrier. Even a small burr on the rear of the carrier will eat away the anodized finish.
The most common cause of damage to the buffer retainer pin is a poorly installed collapsible stock. The lip of the collapsible stock
must cover the edge of the retainer pin or the pin will not be retained in its recess.
Doubling/FCGAlmost always caused by worn, or improperly assembled, FCG parts. Double check your assembly then dry cycle the lower by hand to check for mistiming between the disconnector hook and the middle hammer hook. The tip of the disconnector should
almost touch the middle hammer hook when you cock the hammer by hand. Keep something soft, like your thumb, between the hammer and the lower in case the hammer slips. Do not allow the hammer to strike the lower. With the hammer cocked onto the disco,
slowly release the trigger. The hammer should jump up slightly and now be resting on the tip of the trigger. Repeat this several times. The hammer should not fall. With the trigger pulled to the rear, push the hammer as hard as you can against the top of the disconnector, the middle hammer hook and the tip of the disconnector will separate vertically but should not separate enough horizontally to allow one hook to miss the other. Make sure that the disconnector slides easily in the trigger and make sure that the disconnector spring is present and correct.
Make sure that you are not using large pin FCG parts with small H/T pins..223 vs. 5.56Visit the Ammo Oracle http://www.ammo-oracle.com/body.htm#diff KeyholingUsually caused by the wrong twist for the length of the bullet. Can also be caused by the bullet striking a muzzle device. With extremely short barrels (<9”) keyholing can caused by the lowered muzzle velocity combined with a slightly slow twist. Pull a bullet and make sure it is the right weight, then chronograph the load if possible. Make sure that the bullets are not striking an intervening obstacle. You can confirm the twist in your barrel with a cleaning rod, a tight fitting patch, and a tape measure.