HK MP7-PDW / Custom 5.7 x 28mm

This is a custom build that I think will get some people excited. I’m still very much in the “developmental” stages of this project but I wanted to post the ideas and drawings for now. The general plan is to have a working semi auto “clone” or similar replica of the HK MP7 in 5.7 x 28mm. The original HK MP7 uses the 5.6 x 30mm round but I am most likely going to go with the 5.7 for a couple of reasons; less expensive and more common ammunition, gives me another gun to shoot my 5.7 rounds out of other than my PS90, utilization of the FN PS90 barrel and other P90 bolt parts. Its not a debate about which is a better round its simply those deciding factors.

A couple of the main points for this build are:

  • Custom trunnion and receiver
  • High quality “airsoft gun” body and small parts
  • PS90 barrel
  • Custom milled bolt
  • Custom FCG
  • Modified/custom magazines
  • MP7 optic

Receiver Constriction

The plan for the receiver is to mill a steel barrel trunnion and weld side plates to it to act as the main housing and to give the bolt a channel to slide on. This will also take most of the stress and heat away from the “plastic” or synthetic housing. This receiver should fit into the housing from the back and be secured with screws and push pins.


Synthetic Body/Stock/Housing/Chassis

Some of these airsoft guns are very high quality and built to a better standard than some real gun parts. This will only be a housing for the actual receiver which will be steel and any parts that are to weak can be remade or milled from steel or aluminum. I have no doubt that the housing will work as a “stock” for this project just like any other plastic stock for any other weapon. Some of the parts will not be strong enough so they will be “beefed up” and it will all be made to work, 1 way or the other.

Bolt Construction

The bolt will be a custom milled bolt/bolt carrier assembly. It will most likely use a PS90 firing pin and extractor. The ejector will be a stationary ejector attached to the inside of the receiver. The ejector will be adjustable so as to help make the gun more reliable. This design is inspired much by the HK USC and UMP bolt but with the PS90 bolt face.

Sketches and pics:

Barrel and Operating System

I will try to use a PS90 barrel and a gas piston operating system like the original MP7. I plan to use a shortened piston and rod from an HK SL8/G36 similar to the G36C operating rod and piston. The gas block will be a custom made block designed from the G36 but made to fit the modified PS90 barrel. This should be the easy part of this build.

Original HK MP-7 Reference Images

These are some shots of the original MP-7 inside and out:


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