Building an RPD-like gun from scratch

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The RedNeckEngineer has blogged about his modern RDP-like rifle build. He opted to make a hammer fired mechanism instead of the original striker mechanism. The striker mechanism works fine in the original fully automatic open bolt RDP, but is unreliable in semi-automatic builds that have to fire from a closed bolt (BATFE rules). RedNeckEngineer used a H&K G3 lower and fire control group to provide a hammer mechanism.

The barrel was cut down to 14.5″ and then a flash hider welded on to increase the length and make it 16″ legal. He removed the G3 pistol grip and replaced it with an AR-15 grip and a mechanism to keep his finger off the trigger unless the rifle is push forwards, allowing for easy bump firing (this is not pictured in the above photo).

[ Many thanks to Commander Zero for the tip. ]


Steve Johnson

Founder and Dictator-In-Chief of TFB. A passionate gun owner, a shooting enthusiast and totally tacti-uncool. Favorite first date location: any gun range. Steve can be contacted here.


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  • Anthony H.

    Still got some tweaking to do, but from what I can see in the video, I like it.

  • SGT Fish

    looks kinda M60 like. which is cool. i ordered the DSA RPD carbine and im just waiting to give it a good testing and ill write up a review

  • tincankilla

    Cool to build bumpfiring into the gun – would be interesting to design a semiauto from the ground up with an integrated bump slide and ergos to make it more stable.

  • SiloZen

    Nice, funky that he’s got the AR Stock with it, wonder what he’s done with the blocky handguard?

  • Axel n

    Awesome hobby project! Very inspirational!

  • Raoul O’Shaughnessy

    Looks like something out of one of those “homemade guns of Libyan rebels” videos on YouTube.

  • Lance

    Looks fun hope he makes it less bulky.

  • Tony

    Thank you for your post. I didn’t know the RPD was striker fired.

    • http://theredneckengineer.blogspot.com James

      It’s not striker fired originally, it’s actually an open bolt design.
      The common method of making these run in semi auto is to machine the bolt carrier to accept a striker rod, and then machine a striker block that is retained by a modified trigger group. It’s not an easy gun to work around and have it light off primers 100% of the time, unless you use a hammer system or build a post86 sample that stays open bolt.

  • Nicks87

    Awesome, I love it.

    This is what freedom is all about!

    • David/Sharpie

      You talk about freedom, and yet you constantly whine about zombie items?

      I guess it’s only freedom if you agree with it eh?

    • Mike Knox

      Shame when everyone has that freedom but hardly anyone ever uses it..

  • gunslinger

    kind of reminds me of a guy on ARF who was trying to build his own PS90 style PDW. Didn’t read through his posts though.

  • http://theredneckengineer.blogspot.com James

    Thanks for the link!
    The bumpfire stock was just a mishmash of stuff I had laying around. I wanted something as close to full auto as i could get without a tax stamp and when the stock works right, it’s pretty dang close.
    Like with my home built .50 BMG, I’m just never satisfied by the way my builds look, so I’m probably going to redesign the stock.
    The hand guard was crap. It looked much better in my head than it did on the mill. I think making one out of aluminum that closely resembles an M60 would look good.
    Thanks again for stopping by and for the kind words everyone.