3DP Hydra Lower - Magwell quick change system

I wrote the following below in 2024 or 2025.  I haven't done any work on it since.  The only thing holding this project back was documentation and it's done now, I guess, but it's pretty messy.  Releasing neow, DOWNLOAD HERE!!!!

MGI Hydra lower magazine-well quick change system.  Longform rambling.  Caffeinated and drunk, need to type fast before I lose interest again, so here goes.  Been working on and off over a few years, largely ignoring it for months and years at a time.  But it seems this year there is a growing interest in the MGI Hydra system (due to the new Lima Six beltfed system using it) so I want to finalize and release what I have.  Actually, I'm hoping someone picks this up and makes a U-bolt version.  I tried it myself but the U-bolt model has too many curves and bezels - too many polygons - and my Windows 95 era model editor can't open it and I refuse to learn new software.  So if anyone wants to take a stab at it that would be cool of you!

Different Hydra Projects

It's compatible with MGI Hydra and Windham Hydra magazine wells.  I tested an original MGI Hydra lower with my printed front-ends and real MGI Hydra magazine wells with my lower and they work both ways.  It uses a GhostGunner AR-00 (owned by DefCad) buffer tower as a basis, and I referenced the "Grandmas Apple Pie" receiver to verify dimensions.  I know Defcad and co is problematic, but they're the only guys that have designed a dedicated universal threaded buffer tower for this specific purpose.  You can actually buy the buffer tower from a few other places such as KAK Industries, but they don't include screws (m3x12mm and m3x16mm).  Also I will include a "dummy" buffer tower so you can print it and use it for 22lr builds, forward spring uppers, or bolt-action uppers.

It works with real magwells! But you should print them instead when they become available.

Actually, there is a MAC-10 threaded buffer adapter that is made of steel, and that is where I initially started this project on back in 2018.  There is only one guy that makes these and that is KeepShooting.  They were out of stock for about 4 years straight and just started selling these again this year (2024), so supply issue is another reason I moved away from those (update: I just bought the last one again in 2025 so EAT MY ASS, SUCKERS - they're gone now).  I bought about ten of these back in the day and I think I was the reason he sold out the first time, so who knows how many they have in stock this time.  They're indestructible, but you have to grind a lot of material off the top. The thing is really bulky, so I had to redesign a new grip—simply making an AR grip adapter won't work because of the excess steel material along the bottom of the unit. Also the MG grip I made for this is ass and I don't like it, but I included it because it kinda looks neat-o.

MG42 Mini Grip

Assembled Hydra Lower with GG Buffer Tower

The Defcad Ghost Gunner AR-00 buffer tower works right out of the box and gave me less headaches.  I actually just designed this Defcad buffer tower version within the last thirty days and have been happy with it.

Improvements over older versions (model name: "Keep Shooting Mac 10 Adapter Lower" that was never publicly released):

• Narrowed hammer channel for increased material thickness (open pocket version available for drop-in trigger packs)
• Rounded interior corners for enhanced structural strength!
• Hydra Magwell interface is stronger as a result of above mods
• MOSTLY normal-looking AR15 aesthetics (as opposed to the old, bolted Frankenstein look)

I did toy with the idea of metal inserts that would encompass the magwell engagement area, but the fact is it really isn't needed.  There is very little stress on that joint as the upper receiver acts as a sort of straightening brace to keep it all aligned.  I did strengthen the wall where the hammer is at rest.  It wasn't necessary as you should not dry fire the hammer without assembling the upper and a bolt to absorb the hammer strike.  Even the original aluminum MGI Hydra lower will break the wall if you dry fire it without a bolt carrier in place.  I stress-tested these by breaking them with needle-nose pliers and the narrow hammer-way with rounded corners feels significantly stronger.

9mm Largo Destroyer Magwell, WIP, circa 2019

The main receiver can be printed in one go at 100 infill, less than 14 hours and no support needed.  The only thing that might be recommended supporting is the underside of the grip hole where the round protrusion would insert into.  Why did I design it like that?  Its dumb, yeah, but it's a holdover from when I was designing this using the KS Mac-10 adapter as a basis for it's steel buffer tower.  That threaded adapter came with a stout 1/4-20 bolt going through that area and I still want to be able to use that midget MG-42 grip that I designed for it.  Also the main receiver portion has to be printed exactly upright, as I presented it in the default STL layout, in order for the magwell to fit perfectly, so don't try any funny diagonal prints.

Same lower as above, with an MGI STANAG magwell and 22lr bolt.

Future plans for interchangeable magwells - aka magazines that I like (in no particular order):

AR15 magwell (already got something done but it's ugly and needs assembly and more testing)

Dual button Uzi/Colt magwell

P08 Luger stick and drum magazines

PPSH 41 and 43 magazines

Star Model A magazines

Destroyer 9mm Largo magazines

Marlin 795 magazines

.45 1911 magazines

MP34 magazines

Sten Magazines

Maybe P320 magazines in .45 and standard

Maybe I'll make an AK magazine front-end

Oh yeah, ASSEMBLY REQUIRED.  Also buy 6-32 screws, Allen drive, button head, variety length pack.  In addition to that, I suggest you buy 2-inch screws and just cut them to whatever size you need. See link below.

LINKS:

Ghost Gunner AR-00 Buffer Tower - $30, comes with 12mm, 16mm, and 20mm screws.

Perfect Ghost Guns - $25 - same, 5 dollars cheaper.

Middleton Made - $26 - Comes with 4x 25mm screws.

KAK industry - $26 - no screws included.

Amazon 750 piece M3 screw set - $10, Lifetime supply of screws here. 12mm, 16mm, and 25mm length screws included.

Amazon 100 piece 6-32 fun pack - $10.  God's chosen thread pitch (imperial 32 tpi) in God's chosen drive - Allen head.  Needed for all my projects in some capacity.  The grip section, grip attachment, and grip screw use 6-32 screws.  The grip screw has to be long, but not too long.  It's not included in this set.  I'll be honest, just go ahead and buy every 6-32, 8-32, and 10-32 screw in every length from 1/8" to 2" because I'm all-in on the 32 tpi pitch.

Lima Six - Hydra Magwell - Twitter post.  It was listed on their forums by a user but it's gone now.  I don't know if I should be sharing other people's work without permission, so you'll have to ask them.

randcrap: 3dp baseplate for aluminum USGI AR15 magazine

I was given some aluminum USGI magazines from the armorer that were missing baseplates for some reason.  I didn't want to throw them away but I didn't want to spend 5 dollars (including shipping) on individual baseplates for whats just a $4 magazine, so I whipped this up.  As far as I know, there is not a 3dp AR15 mag baseplate anywhere online for a regular old aluminum magazine because I tried to find one before making this.

I should have made a lip near the front so it couldn't be pushed further into the magwell, but I didnt want to waste any more time on it and it's not really needed.

Two versions, thin and thick.  Might need a flat head screw driver.  Thin can mostly be installed without tools.  The thicker one might need a little bit of persuasion with some needle nose pliers.

Download Links:
Thingiverse
ODC

VZ61 Multipiece Lower, Release V1, Public Beta

 Yeah, I'm slow.  Truth be told, I have not edited this much since 2021, and have not tested it past 50 rounds.  In that time I had a lot of important stuff going on and kind of just forgot about it.  I am releasing this to the public as an open beta test.  I want to move on with other projects, but I will eventually finalize this.

Montage of old versions.

The only thing I did recently was make a PDF instruction manual and create a screw jig that has not been tested.  The VZ61 frame I tested in the video was a slightly older variant that actually stretched lengthwise (to the point where the upper would not close) and had noticeable egging of the screw holes, which I addressed by adding more material around the screw holes.

That being said, print at your own risk.  ONE DAY, I'll actually return to this project and finish it.

For more detailed build instructions, read the PDF included with the files.  Please feel free to post any questions, suggestions, or ideas in the comments section here.

THE LINK ON ODYSEE!!! CLICKY HERE!!!

More info from the included PDF:

Note: This package was made and released in August 2024. I am uploading a print file that I haven’t touched since 2021 and forgot about it because I had a bunch of stuff going on. Currently outside of the country until 2025. Trying to wrap everything up and release it now that I have a bunch of down time, and everything is based on notes and old pictures. Will update this documentation along with updates to the STLs in the next year.

INTRO: Yes, there's already a CZ61 / VZ61 Skorpion that takes an AR15 FCG (special thanks to FreeMenDon'tAsk's VZ61 which I used to compare/verify dimensions) but mine can be printed piece by piece at a time (for smaller printers) and replaced when worn out. Also I hate leaving my printer on for more than 12+ hours for large prints. You can inconspicuously print these pieces on school library or company printers and not arouse suspicion (tell them it’s Radio-Controlled Car parts). Additionally, my front pivot pin area is reinforced with metal so it doesn't need an ungainly thick pivot area. Some of individual printed pieces are simple enough that they can be replicated using metal bar stock and simple tools. The ultimate goal is to have a mostly metal (if not all) receiver.

Future Updates: There's still some minor fixes I need to do, like add more material around the screws so they don't crack. Maybe make the front and rear side plates one piece. I also want to make a semi-auto VZ61 FCG version since I now have several sets of these trigger groups that need a home. Also maybe Walther PPS Mag-well since I have a bunch of these magazines.

The final phase for this is to create a set of jigs so that you could re-create the 3d printed parts out of metal stock - at least for the side plates. The front, center and rear trunnion would always be 3d printed due to their complexity, but I want to try casting them from aluminum, brass or zinc some day. I haven't got that far yet because I got bored of this project so I'm trying to push the files to the public for testing.

Old footage:

VZ61 Proof of Concept, status update

Video of my own version of the VZ61 “SkARpion” receiver - so called because its a Skorpion with an AR fire control group.  Yeah, its been done before, but I like mine better because its metal reinforced, user-assembled, and will include modular magwells, grip assemblies, and FCG containers.  It isn’t dead and I havent forgotten about it.  It needs a few tweeks before I am ready to release it to the public, hopefully by Christmas.

Printer Maintenance log

 Went about a whole year without doing any serious PM and calibrating on my Ender 3, aside from minor bed level adjustments.  It finally started seeing problems after running 8 hours a day for a whole year, with a week of rest per month when I left town.  Fortunately these are fixable along with most parts of the Ender.

Space between lines - not good!

The first thing I noticed was spaces between lines on the top layer, then failure to extrude.  At first I suspected a clogged nozzle, then I thought the table had somehow shifted away from print head causing thin lines.  I guess it was a combination of both (and I suspect a weakened extruder feed might be the next problem area in a few months).  I attempted to disassemble the print head for cleaning but then the aluminum heat sink broke from the heating block!  There was burnt carbon crud in the nozzle and hotend.  Luckily I had a spare printhead with hot end assembly.  The old Bowden tube was trimmed to it's extreme shortest length from previous maintenance.  Everything had to go.  I also discovered that saving brass print nozzles and cleaning them is a waste of time since you can buy a whole bag of 10 for $15.

Bowden tube should touch the nozzle.

After installing the hot end assembly and leveling the bed, I was getting horrible stringing.  It was from where one layer ended and the printhead moved to the next layer, leaving a trail of residual filament behind.  Settings needed to be re-adjusted.  The first thing the experts say is to modify retraction settings.  I used this guide to help troubleshoot.

Stringing like dog fur.

Modifications made and results:

• Changed extrusion temp from 217c to 208c - no change.
• Reduced print speed from 40 to 35 - no change
• Increased retraction distance incrementally from 5 to 10 - success!
• Retraction speed from 50 to 55 - minor improvement.  It should be noted that this might be too fast and cause the extruder gear to rough it up and cause wear.
• Changed top layers to 2 from 0 (might have been accidently changed at some point?) - no change
• Infill gap overlay from 30% to 70% - very minor improvement.

Troubleshoot by incrementally changing settings.

Helpful troubleshooting links:

All3dP - Fix stringing guide
All3dP - Guide to gaps between lines and other layer problems

Scrapwood shelf, 3d printed legs

A low-poly shelf leg, roughly seven inches long, to be attached to a scrap piece of 3/4" thick board to be used as a shelf. Link here on Thingiverse. Use it to display your gun stuff! Actually it's to make room on my kitchen countertop for a coffee machine, but you can put some heavy stuff on it.

Mockup - Sig Nambu?

No, just kidding. This is actually a mockup of my p08 magwell shoved into a p320 testing jig I made. I actually was testing if this unholy union is feasable and it technically should be with modification of the slide holdopen device. I originally stated I wanted to keep the original mag catch but there's enough free grip space to go back to the drawing board and make something more modern. Modern proprietary magazines are the devil.

Bringing back the 9mm stripper clip (work in progress)

Started out building an MP34 9mm Steyr magazine well.  Ended up going all the way with a stripper clip loader just like on the German MP34.  Will eventually release a Colt/Uzi magazine version for public consumption, the MP34 version is my personal project.

It works but needs a few tweaks.  Used 40 S&W rounds for testing as that's what I had immediately available.

WIP - Functional P08 Luger Magwell... for reasons.

Work-in-progress - Making a P08 Luger magazine well assembly.  Why?  To use P08 Luger magazines, duh!  I want a pistol caliber carbine that uses Luger magazines.  But first, a quick look at my design process.

Directory of old, obsolete files

Close enough to work with.

I usually start out with a reference which I download from some online repository such as Grabcad.  The P08 Luger frame I used may be in spec, but it does not translate directly 1:1 when printed.  I used the magazine body to get a rough shape and worked from there.  All those "p08_magwell_*" represents a test and a subsequent improvement.  It's a slow and tedious process.  I have also played around with a 3d-printed mag-catch but was unsatisfied with the results.  I think one is possible, but it would not be compact - it would have to be some bulky AR-Glock mag style mag catch that sticks out of the side, which would be fine for a carbine design but not a compact pistol.

The current iteration utilizes a regular p08 mag catch and spring.  I don't like the flat spring as you'll see below - it's really finicky.  Actually - one of my previous designs uses a clever (if I do say so myself) install process where I got rid of the flat spring and utilized an AR15 disconnector spring.  You just push the mag-catch deep in, rotate it and let go.  But again, that needs more space for a coil-spring housing and it really gets in the way of the trigger finger.  I guess those German engineers knew what they were doing.

p08_magwell_1_02b - spring housing is off.

Testing new spring housing position.

Added angular cut and some efficiency modifications.

Also added spring channel.

Properly contoured to the p08 Luger - and it is print-efficient.

The angle of the magazine is so extreme that it will not fit in a regular AR15 with a simple adapter block.  The lower itself must be re-designed to fit the magazine.  Eventually I will release the p08 magwell as a stand-alone model, my own custom version of U-Bolt AR15 lower, and a Sten magwell.  My ultimate goal is design a semi-auto MP-18 that utilizes both p08 stick magazines and drum magazines.  I don't think the original MP-18s took the stick mags, but mine will.

Still have lots of work to do.

See also: Glock magazine Sten on Reddit, which kind of inspired me.

Replacement Latch for Black & Decker Power Tool Case

It's a latch.  Pretty exciting, huh.

I found a nice carrying case for a Black & Decker power tool set lying against the dumpster, complete with an un-used power drill, sander and jigsaw!  But they were missing their batteries, so I tossed them.  Besides, I know better than to mess with those cheapo Walmart brand power tools.

The case itself was missing latches and was a little dirty but otherwise looked good.  I quickly measured with calipers, whipped a design in CAD and printed it.  Close match, but not quite.  I only printed a reduced profile of the latch, at about 1/8" width which saved time and material - a 4 minute print job.  It took 5 iterations and testing until I got the design just right and then increased the width to the final size of 1.070"

Latch dimensions:

Rod diameter: 0.155"
Rod to Rod (distance between centers): 1.070"
latch width 1.070"
latch length 1.55"

Had to adjust the round half-hole, the latch-claw,

and distance between those two.

Conveniently, my AR pistol lower and two pistol uppers fit right into the case.  I might print some inserts so that they can rest without wiggling around in there;  maybe use some Velcro straps.  I'd like to be able to store several Sig P250's, some spare slides, magazines and grip modules in there, along with plenty of room for ammo.  This project made me realize that, despite there being more sub-gun and short-rifle owners these days, there are not a lot of laptop-size hard gun cases on the market - at least I don't see anything like that when I visit Academy, Walmart or Cabela's.

You can download it HERE on Thingiverse.

The case with fresh latches

Latch open

Latch closed

Pistols with accessories.

Or maybe a case for my AR pistols.

skARpion vz61 - partitioned prototype - part 2

Finished basic partitioning of VZ61.  Ugly, but there it is.  There are four connecting sidewalls (one on each side, purple, red and teal pieces in the pictures below) which can be printed flat without supports.  The rear buffer (yellow) can be printed on its backside without supports.  I think the front piece can be printed without supports.  Middle piece (green) is complex and definitely needs support and should be printed upright.  The grip piece (blue) should slide in upward and will be pinned in place.

skorpar15_partioned_v0_90c

Untested; not ready for distribution just yet.  Soon, though (this year, sometime).

To do:

• Round out the rear connecting walls a little bit to be aesthetic and add material around screw holes
• Make the rear connecting wall follow the angled contour of the middle piece and mag well area.
• Triggergaurd - a single 3d printable one or an AR15 triggergaurd adapter
• Add pin holes on grip mount
• Add an optional buffer tube adapter
• Alternative versions for an AK grip or my custom MG42-styled grip.

Top view

Part one

WIP: AR + vz61 Skorpion hybrid - "The SkARpion" - part 1

Work in progress for a 3d printable VZ-61 that uses an AR15 FCG and is printed in small sections.  "SkARpion?"  Pretty terrible name, I know.  This design is based on FreeMenDontAsk's design which you can find on DefCad.  It used to be available on GrabCad but I guess it got deleted by moderators.

Initial partitioning.

I personally hate 20+ hour long prints and want to print the pieces in smaller, easier to manage sections.  This way I can tune the receiver to my printer/filament and not have to re-print the entire thing if something is screwy.  Also people with small print beds would hopefully appreciate this.

The front and back pieces should not require any supports.  The middle one will probably need support on the bottom.  The slightly clear green wall is one of the connector pieces that will have holes that will screw all the way through to the other side of the receiver.

Not really high on my list of priorities, but I wanted to show a proof of concept.

Progress report: Magazine walls done.  Walls should not need supports.

AR15/1919 hybrid thing

I've been messing around in CAD software and I recreated parts of a Browning 1919 and an AR15.  My idea is to create an unholy union between the two.  Basically it's a heavy-metal receiver shell that you can attach an AR15 upper to and it uses an AR FCG, but it handles like a Browning 1919, complete with spade grips and can be mounted onto an M2/M3 tripod or a standard vehicle mount.  There wouldn't be any real purpose for this, but I'd like to put a FM-9 9mm belt-fed upper on it, or a Fightlite Industries MCR.  Basically the fun of owning a Browning 1919 but with cheap ammo.

A flat-based AR receiver in progress.

Browning 1919-like receiver with an AR15 upper.

The extension below the bottom plate is a protective housing for the AR15 fire control group.  I could have just cut the finger off and avoided that unsightly extension, HOWEVER, I wanted to be able to use off-the-shelf FCG units such as the Fostech Echo Trigger without having to modify it.