US Soldier using an experimental flat-top receiver Colt Model 656 variation on the M16A1, with an M84 Scope. Vietnam, late 1960s period.

https://lemmy.world/post/44689132

how effective were those in a environment where you cant even see past 20m ?

Don’t assume every square inch of Vietnam is triple canopy jungle so thick that you can’t see past 20m in. Designated marksmen were recognized as useful, by both Northern and Southern forces.