The HK tool for adjusting elevation on the HK91 and other HK rifles/carbines goes for over $80.00. There are cheaper knockoffs, but even they are $50.00 and up. I discovered a YouTube that demonstrated a cheap and easy alternative. You just need to find a pair of needle nose type pliers with a really small tip (and I mean MUCH smaller than average). This generally means something designed specifically for either jewelers or electricians. It allows you to engage the two spring loaded locking plungers around the inner barrel. Then you can raise or lower the rear sight by turning it clockwise or counterclockwise. Works great. I have to wonder why HK made elevation adjustment so difficult on their rifles and carbines, though, considering its intended application being military. Maybe they didn't want ordinary grunts messing with them once their training officers supervised the sighting-in procedure at the range.
The mindset in Europe at the time the H&K was invented was that armorers should zero rifles, not soldiers. Most European soldiers at that time got very little marksmanship training, so the thought was that 9 out of 10 times the individual soldier would adjust his sights incorrectly, making his weapon less effective. Elevation adjustments are accomplished by the diopitor only. It has been that way in Europe for about a century. Elevation of a tangent sight only, but actual zeroing of a weapon was done at the depot level.
