Collapsable HK Stock Build

The #1 community for Gun Owners of the Northeast

Member Benefits:

  • No ad networks!
  • Discuss all aspects of firearm ownership
  • Discuss anti-gun legislation
  • Buy, sell, and trade in the classified section
  • Chat with Local gun shops, ranges, trainers & other businesses
  • Discover free outdoor shooting areas
  • View up to date on firearm-related events
  • Share photos & video with other members
  • ...and so much more!
  • SwerveAM

    Member
    Jun 26, 2011
    51
    Just finished up with a version to get the reverse stretch up just above 29" overall length. Extension for the A2 is about 5.75" to get there, perfect for those of us who prefer that "extra" length of pull :D


    20161002_204140%20640x316%20400x198.jpg


    20161002_204414%20640x305%20400x191.jpg


    20161002_204447%20640x480%20400x300.jpg


    20161002_204518%20640x480%20400x300.jpg


    Also started a version for my HK53 clone (started life as a Vector 93 pistol), which also works on the HK91.

    HK91%20Concept%20400x246.jpg


    Next up my MPX (stamp due any day now!) and gotta get on that Tavor!

    Very cool design
     

    Slim

    Active Member
    Sep 13, 2015
    489
    HoCo & Worldwide
    Here’s my latest plan. 6” & 3” threaded rods. 1/4”x20. Threaded couplers as inserts in the stock body. Held in place with epoxy, maybe pins if necessary.

    The furniture nuts will be between the buttplate and a dual-layer insert (kydex) with clearance to the heads in the rearmost later. Hex bolt holes accessible through the buttplate.

    Threaded portion shown extended is ~2.3”. I can stretch that a little bit with a longer lower threaded rod.

    Thoughts? I’m not an engineer, so constructive feedback & tips are welcome.
     

    Attachments

    • 25F548E7-1795-4B78-92F1-271150964885.jpg
      25F548E7-1795-4B78-92F1-271150964885.jpg
      46.7 KB · Views: 427
    • E1F457A9-7E7D-4F60-8CBD-D318CC130834.jpg
      E1F457A9-7E7D-4F60-8CBD-D318CC130834.jpg
      48.5 KB · Views: 427

    Hawkeye

    The Leatherstocking
    Jan 29, 2009
    3,971
    So you'd adjust it with a hex key by turning each bolt? That's going to be some slow adjustment! (Not that you'd ever have to adjust it, really, but still.)
     

    Slim

    Active Member
    Sep 13, 2015
    489
    HoCo & Worldwide
    So you'd adjust it with a hex key by turning each bolt? That's going to be some slow adjustment! (Not that you'd ever have to adjust it, really, but still.)
    Yes, yes, and exactly.

    I studied some of the 3-gun, trap, and other competition shotgun adjustable buttplate designs. Many of those are adjustable to fit the shape of the shooter, vice clothing, armor, etc. the Magpul PRS stock with the adjustment knobs fitted into slots in the stock is a clever commercial way to do it, but way beyond my ability.

    To your point, it’s not just slow, but tedious too because the user will have to adjust both almost simultaneously, or alternate from one to the other, because the buttplate won’t want to flex/angle as it extends/retracts. I’m not sure the spacing between the bolts will permit two tiny IKEA S-wrenches to fit and be turned in parallel, but that would be ideal.

    As for how often I’ll extend it? Ideally just once to show you guys here in the forum, so someone can build the next generation on their MP5A2 SBR build! After that, I’ll be a “just in case” thing, like the copies of my Form 1s that I’ve never shown anyone.
     

    Slim

    Active Member
    Sep 13, 2015
    489
    HoCo & Worldwide
    Been working on tearing down two A2 stocks for this project.

    First one is a USA-made clone from HK Parts.net. Clean seam between body and buttpad, but nothing to really grab onto or a gap to pry. Put the buttplate in the vise and put angular pressure on the stock body. I heard a crack and the glue gave way, then it came apart.
     

    Attachments

    • C009F5A6-1116-4807-98C3-4B933953370B.jpg
      C009F5A6-1116-4807-98C3-4B933953370B.jpg
      47.8 KB · Views: 378
    • 5DAF5462-91D2-4D1D-8CEB-C2E97265C5D5.jpg
      5DAF5462-91D2-4D1D-8CEB-C2E97265C5D5.jpg
      46.5 KB · Views: 376

    Slim

    Active Member
    Sep 13, 2015
    489
    HoCo & Worldwide
    Second one was a mess!

    Nasty looking glue/weld seam. Tried heat, Xacto knife, prying. Eventually I took a saw too it. It was an inter-generational family project, with my grandfathers mitre jig, dad’s workbench, and uncle’s thin handsaw. Took forever sawing through that glue.

    HK plastic (I think that’s what this one is) is damn stout. Now trying to figure out how to fix the extension/retraction mechanism in there...
     

    Attachments

    • 71185BFF-9A4F-4B80-BCEB-B53025A9C0EF.jpg
      71185BFF-9A4F-4B80-BCEB-B53025A9C0EF.jpg
      79.5 KB · Views: 397
    • F9D4FA38-72C5-4E57-92FD-2C189BBAA256.jpg
      F9D4FA38-72C5-4E57-92FD-2C189BBAA256.jpg
      87.2 KB · Views: 403

    Slim

    Active Member
    Sep 13, 2015
    489
    HoCo & Worldwide
    Necropost for Halloween

    Two years later, still questing for an A2- looking stock that’ll get an MP5 clone SBR to 29”.

    I saw this on Instagram today:
     

    Attachments

    • 5AA52982-CB22-4E9F-BA38-85CD6DCC44C3.jpg
      5AA52982-CB22-4E9F-BA38-85CD6DCC44C3.jpg
      55.8 KB · Views: 274
    Dec 15, 2012
    22
    Md
    Funny I just stumbled on this thread all these years later, but both of these designs, are the two that I was talking to my friend about doing for my SP5k PDW. Problem is, with it being a K, I’m more worried about being able to keep folder, and as such, I’m just going to be going to AOW (two handed “pistol”). I’d actually planned to do it on a skeletonized UMP style folding titanium stock. I had figured on getting ultra fine thread 1/4” stainless rod, and running it through threaded tube… for ultimate buttpad placement precision. Figured the only modification from the UMP looking stock I would need, is the lower 3” horizontal tube.
     

    Gcs7th

    Ultimate Member
    Jan 26, 2012
    1,280
    AGC
    Second one was a mess!

    Nasty looking glue/weld seam. Tried heat, Xacto knife, prying. Eventually I took a saw too it. It was an inter-generational family project, with my grandfathers mitre jig, dad’s workbench, and uncle’s thin handsaw. Took forever sawing through that glue.

    HK plastic (I think that’s what this one is) is damn stout. Now trying to figure out how to fix the extension/retraction mechanism in there...
    Slim did you ever make this happen? Or do you have a box of broken HK parts.
    Would anyone happen to have the tubing sizes that were used?
    Tubing looks to be close to the internal diameter of the stock this looks like a very nice build on the second hand I bet this part could be easily 3d printed to adapt for any size tubing available.

    For the OP out there, amazing job. This is on my list still. One day…
     

    Collector98

    Active Member
    Jan 18, 2015
    271
    Slim did you ever make this happen? Or do you have a box of broken HK parts.

    Tubing looks to be close to the internal diameter of the stock this looks like a very nice build on the second hand I bet this part could be easily 3d printed to adapt for any size tubing available.

    For the OP out there, amazing job. This is on my list still. One day…
    I just bought an AP5 and am hoping to do this in the next few months.
     

    Collector98

    Active Member
    Jan 18, 2015
    271
    I just got a stock in today and decided to start working on it. I cut the end of it off with a miter saw and got a super straight cut in about 5 seconds. I then took some measurements and am currently printing a test piece. The idea is to screw the buttpad to the "arms" mocked up in Fusion 360, then drill an extra hole in the stock that will just use an extra mp5 pin that goes through a hole in the lower arm to index the length you want. The idea works in my head, but we'll see how it works/fits in real life soon!
     

    Attachments

    • 20220829_184712.jpg
      20220829_184712.jpg
      227.7 KB · Views: 76
    • 20220829_190035.jpg
      20220829_190035.jpg
      185.4 KB · Views: 76
    • 20220829_204742.jpg
      20220829_204742.jpg
      185.1 KB · Views: 74
    • 20220829_204749.jpg
      20220829_204749.jpg
      349.9 KB · Views: 77

    smdub

    Ultimate Member
    MDS Supporter
    Nov 14, 2012
    4,644
    MoCo
    Does the new stock have the 'rubber bumper' buffer inside? Mine that is one pc molded plastic like that doesn't have a MP5 buffer. Just a metal plate. I think it was from an older G33 w/ the buffered carrier. You don't want to run the gun w/o a buffer.
     

    Collector98

    Active Member
    Jan 18, 2015
    271
    Does the new stock have the 'rubber bumper' buffer inside? Mine that is one pc molded plastic like that doesn't have a MP5 buffer. Just a metal plate. I think it was from an older G33 w/ the buffered carrier. You don't want to run the gun w/o a buffer.
    Mine just has the metal plate on it. I've read conflicting things about the buffer's usefulness on 9mm, but I may just be safe and throw one in anyways.
     

    Collector98

    Active Member
    Jan 18, 2015
    271
    Final(ish) version. It's 3D printed arms that collapse into the buttstock with varying lengths of adjustment using friction fitting pins to index the length. I only had blue filament, so for the time being, that's how I'll keep it.
    20220831_165508.jpg
    20220831_165615.jpg
     

    Collector98

    Active Member
    Jan 18, 2015
    271
    Alright, I just decided to paint the pins and it looks awesome! At least to me. It's not perfect, but it locks up tight in the closed position, so I'm very happy with it!
    16619844825393251803000614756165.jpg
    16619845066507127562020725616430.jpg
     

    Collector98

    Active Member
    Jan 18, 2015
    271
    That looks amazing. Would you be interested in doing this as a service for paying customers? Unfortunately OP seems to have disappeared.
    I'll send you a pm. I remember you asked about it a little bit ago, but I just wanted to tweak it a bit before reaching out. :)
     

    Users who are viewing this thread

    Latest posts

    Forum statistics

    Threads
    274,928
    Messages
    7,259,428
    Members
    33,350
    Latest member
    Rotorboater

    Latest threads

    Top Bottom