I have an Ostler one and the gap is 5mm but I find it better with it taken out by 1 turn so about 6mm.
HW 77 V glide kit by Steve Pope
8-40x56 Custom Shop.
HW 101. Big Nikko. Ginb FT Stock.
Webley Omega, Gas Ram.
Rohm Twinmaster Trainer.
Red Dot Sight.