I'm not sure how popular it is to do a DMR from a G36 like i've done, but i thought i'd share my tip to the world anyway.
Instead of modifying anything in the gearbox, i made it so the fire selector physically can't push the selector plate in full auto.
What i did was that i took the gearbox (which is v3) out of it's handle and glued a small peice of plastic to the side of the handle. I have this picture to illustrate it:
In this picture, the fire selector is in the SAFE position. When moving the lever to SEMI, that's where it stops. The small peice of plastic will prevent the lever from moving further and thus preventing it from ever going to AUTO.
Quite simple, very cheap and it can all be reverted to the original state when needed.
This might be used on other rifles too, i'm not sure. I at least hope it might help someone.
EDIT:
I also made another small mod that might be used on more rifles other than the G36, but i'm not sure.
I removed the Selector Plate entirely. Instead of using the Selector Plate to connect the small tinplates sticking out from the Switch Assembly, i connected the tinplates by soldering a small peice of metal between them.
This mod will only work if the firing system is not dependant on the Selector Plate.
*Some explaining on how it works in a G36, for those who are interested*
When moving the Fire Selector to SEMI, it pushes the Selector Plate into position so it connects the tinplates in the Switch Assembly. When moving it to AUTO, the Selector Plate also pushes down the Cut-Off Lever in order to let the gears run without stopping after each cycle.
Removing the Selector Plate will prevent the Cut-Off Lever to ever let the Gearbox do AUTO.
In all, two small mods that both are 100% reversable and will prevent your G36 from ever shooting AUTO.
Yet again, hope this can help someone.
