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Adjusting/Removing/Replacing HK Diopter Rear Sight Drums

I must replace the rear sight drum of my Mp5 clone but I don't know to do.

Could someone make me some instruction?

I have the Rear Sight Adjustment Tool.

1. CLEAR and mount the gun upright so you can work on it hands free. VERY IMPORTANT!

2. Turn the rear sight drum (“outer drum”) looking down into the drum as you do. Note there are 4 notches at 12, 3, 6 and 9 o’clock at the base of the drum inside (“inner drum”), two of which have black detents in them and two do not. Note when you turn the outer drum the area inside the drum (“inner drum”) with the 4 notches also turns.

To adjust/remove the outer drum you must hold those two detents inward against spring pressure using the SA tool while you unscrew the outer drum CCW. This “unlocks” the fixed inner drum from the removable outer drum.

To do so:

3. Have your replacement outer drum close by!

4. Insert the lower (black “lever”) portion of the SA tool inside the outer drum so that the two spring levers on the SA tool enter the two slots in the inner drum with the detents. Hold the lever portion of the SA tool down and firmly in place throughout!!!!!

5. SLOWLY insert the upper “handle” portion of the SA tool into the lever portion. This squeezes the levers on the lever portion inwards which compresses the two détentes within the inner drum freeing the inner drum to rotate separately from the outer drum.

6. Holding the SA tool firmly in the drum you should now be able to freely rotate the outer drum CCW to remove it from the inner drum.

If you cannot, you did not successfully disengage the two detents or you did and let them slip during the process. If so, lift up on the handle portion of the tool @ 1/2 - 1 inch and reinsert SLOWLY and STEADILY and DO NOT allow the tool to tilt or the detents will slip out from under the levers.

7. Once the outer drum moves freely from the inner drum and turns around the SA tool unscrew the outer drum CCW while holding your hand/fingers around where the detents are waiting SPRING LOADED and “anxious” to escape forever should they slip out. If you tilt the SA tool at this point those detents and the springs behind them will vanish.

8. When the outer drum is free CAREFULLY remove the handle portion of the SA tool (Leave the lever portion in place!), place the new drum over the lever portion of the SA tool and screw it fully into place CW.

DO NOT remove or allow the SA tool to wobble during this process or the detents will be gone.

Some folks like to place a clear plastic bag over the rear sight assembly in case they screw up.

Good luck. DO NOT consume caffeine prior to attempting this procedure! You will want a steady set of hands.

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