M4/M16 Hop unit strip and rebuild guide
Please use this guide as a helpful tool for when you need to upgrade your rifle. The M4/M16 Hop unit strip and rebuild guide should be used as a guide only and we cannot take any responsibility if you lack the knowledge or tools to carry out the task competently.
This guide will help people who are struggling with stripping and rebuilding the M4/M16 hop unit.
If you’re building one from scratch go straight to the Rebuilding section.
Stripping the hop unit down:
Tools needed are a small flat bladed screwdriver and a Philips screwdriver.
Lay the hop and barrel assembly on a flat surface.
Remove the large spring; most models have a small spring coming from the tab by the third adjuster cog. Mine had a large spring.
Unscrew the adjuster cog screw and then remove the cog.
With the flat bladed screw driver, prise the spring clip off the second cog, be careful these can sometimes ping or you can stab your finger.
Turn the unit over and remove the other spring clip, be careful as well with this one.
Now turn the unit back over and remove the cog.
Now press out the pin holding the hop adjuster arm in place.
Remove the adjuster and hop nub.
Remove the C clip holding the barrel in place.
Slide the hop unit off, I find slowly twisting it helps to stop the rubber tearing as it slides out.
Remove the rubber and if the brass ring comes off, that as well.
Rebuilding the hop unit:
Clean your barrel before proceeding as it’s the perfect time to clean it.
Slide the brass ring onto the barrel and then the hop rubber making sure it lines up fully.
Slide the hop unit on, making sure its all aligned correctly.
Put the C clip into place to hold the barrel in place.
I find it easier when inserting the hop nub, to place it onto the adjuster and hold it upside down as you slide it into place in the hop unit.
Slide the adjuster into the hop unit making sure the spring is in the correct place on the adjuster arm.
Flip the unit over and insert the pin to hold the arm in place.
Now you can insert the adjuster cog, Helps by pressing the hop arm down as you do this so the cog slides in easily.
Flip the unit over and place the spring clip tightly onto the shaft.
Flip the unit over and place the middle cog back onto its shaft and then put its spring clip on.
Place the main adjuster cog onto its shaft and screw the little screw up tight. (one mod I did to my hop unit was with this cog, take a 5.5mm drill bit and lightly run it on the back of the cog, then get a small 3x1mm O-ring and put it on the shaft underneath the cog, this helps to prevent the hop coming off as the AEG shoots)
Slide the spring onto the barrel or shaft (depending on version of rifle) and your now finished.
PLEASE ONLY ATTEMPT THIS IF YOU’RE CONFIDENT. I HOLD NO RESPONSIBILITIES FOR PROBLEMS OR BREAKAGES.