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!
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| 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.
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| 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.
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| MG42 Mini Grip |
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| 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.
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| 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.
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| 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.
