Combinations of barrels and buttstocks
As 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.
Free float handguards
Install your own Free Float Tube - step by step instructions
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 coils off to gain function.
Damage to buffer/buffer retainer
"contact scratches" on face of new carbine buffer
Buffer retainer flying into the gun
Almost always caused by worn, or improperly assembled, FCG parts. Double check your assembly then dry cycle the lower by hand to check for mistiming. 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 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.
Double tap type experience at the range?
.223 vs. 5.56
.223 vs. 5.56 NATO
5.56 .233 differences
Usually 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.