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K-SMG1 project build thread


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So, I started on a new project a couple of days ago, to build a small-ish smg to use the big pile of kwa mac11 mags I have laying around. But I wanted to do this a bit differently and actually start the thread while Im still working on it rather then just post a thread about it once its finished.


So, as is how I usually work, I dont get into a lot of technical detail before I start. I prefer to have a general idea to start with and work around it. This time around I have nothing but a chicken scratch drawing that I did while sitting in traffic 2 days ago. Here it is in all of its barely competant glory:




Normally I do a bit more planning then that for internal parts, of course, but in this case I didnt really need to do that, because it will use a WE trigger pack, which will be a combination of M4 and Scar-L parts (Like the linkage arm for the disconnecter). So most of those parts will already be done in this case. Though I will have to make a new valve knocker since the WE type is unlikely to work with the layout of the KWA mag, which puts the release valve a bit too low..


So like I said, I did already start. I wanted to at least put the fcg and mag in place so that it would be more obvious that its an airsoft gun to anyone looking at the pictures. So to that end I already milled out the pocket for the WE trigger box, and the magazine well into a big block of aluminum. I also did some of the cuts on the underside of the receiver tube so that the frame fits in place. Im not going to do anything fancy for connecting it, just two screws to hold it together.




my camera refuses to focus on anything so the pictures are a bit blurry, but here are the two peices together:




so the next step I think, is going to be doing some shaping on the frame in order to get the trigger and everything in place, since right now just the box fits but without all the parts. Im still going to need to adjust the height that the fcg sits in the receiver but Ill have to do that once I start the bolt. I purposely made it sit a bit low in the frame so that I could shave the top of the frame down in order to raise the fcg in the tube.


One I have the frame shaped and the fcg set to the right height, Ill start working on the bolt and nozzle setup (The nozzle will likely be a custom machined part) and figure out the height that the mag needs to sit at. Then make the barrel and hopup chamber assembly and new valve knocker to compensate for the height difference. Alternately, I might find that its impossible to make up for the height difference and have to switch to using a different type of magazine, or scrap the project. wee.


The last thing Ill work on, once everything else is *hopefully* working, is the stock. It will be a sliding type, with two 1/4" wire legs threaded into a buttplate, with a locking mechanism similar to the one I did on my previous build (The K-S03).


So hopefully this will be a bit more of an interesting thread, most of the time I dont even think of making one until Im 99% finished with a project, But this time I actually remembered at the start. or.. mostly start.

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Ok so heres yesterday's progress. which was all work on shaping the lower receiver portion. So far its looking fairly AR like but im hoping it doesnt wind up too close in looks.


Started by cutting out the trigger guard area:






Then doing the grip shelf:




And lastly I rounded off the backstrap:




The back angle is a bit different from an AR, mostly because I dont have a tool capable of making that profile. But in the end thats good since it will help make it look different. I am sort of stuck with the same basic layout of an AR lower since Im using a WE M4 trigger pack. I can change it a little but all the controls and functional bits are still going to be in the same places.


Over the weekend Im hoping to finish off the lower entirely and then move onto the parts in the receiver tube.


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Finished most of the lower now, aside from the mag catch assembly, which I think will be the next thing. And I will probably shave the whole bottom off to thin out the trigger guard. The mags will have to be modified very slightly to work with the catch I have in mind, which will be an AR style button type (I might even just use an AR mag catch button), but they'll still work in a kwa mac11 afterward.



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Got a bit more done on the lower this evening, mostly spent some time proportioning it a little better and fixing some layout issues like the grip mounting a bit too low. Didnt get to doing the mag catch yet.


It now looks like this. Still some shaping left to do around the trigger guard though.




And the whole thing looks like this so far:




Not quite exact to the cruddy traffic sketch but its close enough that i'm happy. Its not like it was ever going to look exactly like it anyway, once I started doing actual measurements.

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Yes, a simple pipe gun. I really like it. I don't think it matters too much that the lower looks like an AR lower, it is quite unavoidable using a trigger pack and grip from an AR replica.

can't wait to see how it turns out!

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heh, I dont even know what eloxation means! Honestly I was just thinking som decent paint like cerakote or, more likely, alumahyde.


And I dont know if Ill actually wind up using an actual AR pistp; grip. The original idea was to make a shorter more compact wooden grip, But I decided that it was best to mount it the same way, since I will still need the detent in place for the selector axle. it didnt make sense to redesign that part, even though I *might* machine my own selector.

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Not a big update, but I did the lettering on it. I didnt have much time this morning because of work so I figured Id knock this out. Also, I didnt realize it but the mag catch is going to be like.. right between the markings. I should have made them lower. But oh well.






It did give me the idea to reverse the mag catch side though. I shoot lefty so it would make sense for me to put the push button on the left side. Im debating how much I like that idea.

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I think I may well just reverse the mag catch. A heel release could work, but that modification would interfere with the mags working in a mac11 which I want to avoid. Plus it would help change it a bit more from a standard AR so it's good in that way as well.

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I believe OP still have enough meat around magwell to do that.

  • Easier to make with higher successful rate, if OP screws up he just makes another catch with different length/profile
  • Not requiring to mod the mags
  • Less milling and not getting in the way of the markings (why not stamp them after finish? lol)
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Yeah I know what sort you mean. Two problems though. First, I don't have any way to temper a price of spring steel, and second, I don't know if you've ever used a mag catch like that, but they're horrible.


A lot of .22 caliber rifles use mag catches of that sort cause they're cheap to make, but you have to pull them toward you to release the mag. So it's this awkward, usually two handed affair. And I just prefer to avoid it if I can.


Plus the mag catch shelf in the mag hangs out by quite a bit so it would look really janky.


Also, I stamped them before I finished just cause I was pressed for time and just picked spots I thought looked good. I tend to Mark parts early, it seems to motivate me more to finish.

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You can temper spring steel in just about any toaster oven provided it fits. 350-400F for 15min slow cooled is all it takes.

With that setup it's easiest to wedge your thumb between the catch and the mag while the other fingers pull down. Still a two handed affair since you need to support the gun with the other, though it's not like you can freely drop gas mags on the floor anyway. But if you don't like the way it looks then that's that.

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OK, the mag catch has been sorted. I did decide to go with just reversing the direction, and I think it turned out pretty good. though it is.. kinda hard to see in the pictures.






Now, Im not going to start modifying the magazine right away. that will be done later once I determine the appropriate height that it needs to sit at to load. Which means Ill have to start working on the receiver tube now and make the hopup chamber and such.


Though I might change the design of that a bit and go with a rectangular tube receiver now. I think that might be easier to work with for what I had in mind and it would also look a bit different from every other airsoft thing Ive designed so far. So I think im going to order a few sizes of rectangle tube and see if I like any of them.

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And I guess heres one last picture set of the lower. Ive decided I want to try a rectangular receiver, but, since I already have the cylindircal one started Im going to see if I can use that for testing while im waiting for the materials to get here. I also started working out the hopup chamber/trunnion set-up, which im planning on being very simple. maybe just a fixed hopup for now since im not sure how I would adjust it right now. Its something I could design simple now and return to after Ive got everything else worked out.


Im thinking now that instead of screwing the lower into the upper, the trunnion will be pinned/screwed into the upper and that will be used as the front pivot point. in the back there will be another point to put a pi through. Maybe it can be part of a recoil buffer assembly.


But heres the pictures. Ive modified the trigger pack to work like a scar/pdw one with the disconnecter linkage arm, since I figure Im going to need it.






I think this is about as far as I can get with the lower without having an upper to work with so unless I find something that I forgot, i wont bother with any more pics of it. If I wind up using a rectangular receiver, I might attempt to do a folding stock since it should be easy to work the shape of a hinge into the back of a rectangle without looking out of place like it would on a cylindrical one.

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So just an update. I think im nearly finished with it functionally, so i figured id put up a few pictures with the rectangular receiver.








It does cycle now, though not terribly efficiently. Ill have to work on that. But before i do that i have to install the inner barrel and hopup which are in the mail now, Ill be using a kwa barrel and bucking since thats how my loading nozzle is shaped.


Then after its all functioning Ill work on the aesthetics a bit. its a it clunky now but i think i can do something with it.

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Theres a bit of a resemblance I guess. once theres sights on it and I finish the outer barrel Im not really sure what its going to resemble really. and im debating wether to try a folding skeleton stock, or do a collapsing wire stock similar to the mat49 (Though with a machined butt and two arms since I cant bend wire precise enough).


Right now Im happy enough that it just goes pew at all though. But im going to have to do a lot of tweaking to make it reasonably gas efficient. right now Ive basically used whatever I had lying around as stand-ins just to get it operational. But I'll be replacing things like the flute valve and spring, and tweaking the bbu plunger and stuff like that. The return spring for the bolt is from an HFC M9 I think, just something i found in my parts drawer. So theres going to be a lot of things to work on to make it work well rather then just "work".


This project really was to see if I could make a reasonably working BBU. Because I have a design I drew up for a semi automatic APS shotgun that will require a fairly large one capable of compressing a spring strong enough to strip and chamber a shell out of a magazine. And I think thats going to be tricky without first getting a decently efficient standard gbb type worked out.

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I couldnt wait to work on things until the kwa parts arrived, So I started the front sight. Like in the original sketch, its still a seperate part which protrudes  out of the front of the receiver, it also has a step down that slides about 3/8 of an inch into the receiver tube so that it can be pinned in place. Its secondary, equally important role is to have a key that fits into a slot on the outer barrel to prevent rotation.


I think that the extra added length kinda balances out the overall look. I also put some completely unnecessary ventilation holes in the receiver tube, just for some aesthetics. I might even make them a little larger then they are now but thats to decide later. They dont do anything anyway except remove a negligible amount of weight.


So here are the pics:






The front sight itself is a pretty common enclosed ring sight, like an Mp5 or similar smgs, which is what I had in mind from the start but kinda waffled on back and forth for a while. I also considered winged sights like an AR or FAL, or folding sights like a SCAR-L or Colt DOE. I already had my spindex for round parts set up though so it seemed better to go with the ring sight. I can always redo it later if I change my mind.


The whole sight assembly isnt finished yet though. It has no blade in it for actually aiming the stupid thing, and the extension down on the bottom should have a sling point attached to it. Once I figure out how to attach it that is, Havent quite worked that out yet, at least not any easy way.



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