MP40 AK hop mod

This is how I do the AK hop mod and this is a guide to show you how it’s done. Please read the whole guide before picking up a single tool or buying parts. If you don’t feel confident doing the mod then by all means contact me or another gunsmith and ask them for help. All mods are done at your own risk.

For this you’ll need:

My personal choice of parts for this build
Element AK hop unit – Ebairsoft
Element H-nub – Ebairsoft
Vanaras 6.04 247mm barrel – RSOV
Guarder clear hop rubber – RSOV

Here is the standard AK hop unit. As it stands it will not fit and needs to be modified.

Start by cutting the feed tube at the point it necks down. Use a junior hacksaw or similar for this.

Now that narrow part of the hop unit was there for a reason as the main feed tube is too wide to fit in the opening of the magazine. You need to narrow the outside of the tube with a file to make it fit and feed correctly. Work SLOWLY and carefully! Most metal files are quite course and will make short work of soft plastic. Try and take and even amount off all the way round. You only want to take off enough so the it fits in the mag snugly. Make sure to file a bit then test fit it into your mag, keep doing this till you happy with the fit. If you want you can smooth the part you’ve worked with some sand paper of fine wire wool.

Next you’ll need to chamfer one side of the tube to allow the mag feed catch to be pushed to one side. A rough 45′ angle works well. Again file and test fit till your happy. It should push the catch back without snagging.


Right now the hard bit’s done you need to start assembling you hop unit. Pop the sleeve onto the barrel and slide it into the hop unit. Make sure it’s all straight and fit the barrel clip. Then put your nub in and fit the hop arm and pivot pin

OK now you need to take a few bits from the old hop and barrel. They are the hop adjuster/slider and the two barrel spacers

Fit the hop adjuster as you would the normal AK one. Then slide the wider of the two barrel spacers onto the barrel. The ones I’ve done have been a tight fit and needed a bit of widening out with a round file. As always file a bit at a time, a snug fit is key to a good result!
Lastly push the muzzle end spacer onto the end of your new barrel. The muzzle spacer is a bit of a git to remove from the old barrel and my need a little help from some grips. If you break it just wrap tape around the barrel to the required thickness.

Now finally comes fitting your new unit in the gun. The unit is not screwed in like the old one. It is in fact held in place by the wide barrel spacer and the mag well liner. Your new hop unit should sight nice and tight in the hole in your liner. If it’s too tight you can widen the hole or reduce the diameter of your feed tube. If it’s a little loose don’t worry as the mag will lock it in tight when inserted. Ideally you should test fit when filing the tube down in the first place.

Pop your gun back together and your done! Go out, dial in the hop and marvel at your handy work!