Still does not make any sense.
If it only happened on the second shot of a double tap, this is telling me that there is a slight delay with the bolt going into full battery - which does point to buffer spring. One would think you would feel that problem, unless you are anticipating the shot and putting extra torque/flex on the upper causing something to bind.
Lube, bolt quality, cam pin...a few other things to consider, but the spring did fix it.
Sticks
Grasseater // Grass~eat~er noun, often attributive \ˈgras-ē-tər\
A person who is incapable of independent thought; a person who is herd animal-like in behavior; one who cannot distinguish between right and wrong; a foolish person.
See also Sheep
Bookmarks