Little Hole in Stock Rail

[xmetal2001]

What is that little hole in my stock rail on the left bottom of the rail. You can see part of the valve through it. whats it for?

[DYE-BaLLeR]

i think i kno what ur talkin about, its if u want to hook the bottle adapter up to under the valve instead of the grip

[Tunaman]

That is the sear pin you see...not the valve...I believe