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Custom m4 base WWII FG-42 replica (late version)

11K views 44 replies 6 participants last post by  CacheFlow 
#1 ·
Got a comission job coming up. client wants a FG-42 replica with a base of a m4 aeg. figured i'll document the build process.

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Background: client has realistic expectations from this build. will take a month or north. aware magazine will not be correct placement, and aware an airsoft version exists already $1200+. appreciates the use of standard m4 aeg magazines and 3d printed parts will be lighter.

my background: this is just my hobby, ive built custom uppers before and have done commissions before as long as the client is realistic in expectations. so far 100%

build thoughts:

90degree magwell and hopup unit. i think this part will be the most mind/labor/time intensive. I have a 3d printer at my diposal so it should make quick work of getting the right features and silhouette. (stock, handguard, and grip will be shaped/added and wood colored)

i found a base of a JG polymer body M4 with a full stock. going to 86 the upper completely and reshape the stock.

Another challenge will be the bipod interfacing strongly with the upper. if the upper is mostly 3d printed, and so the outer barrel, the inner barrel provides some strength. if you put a bipod in the front, there will be a lot of force on the inner barrel. unless i run a steel rod or bar stock down the length. bipod will have a rod running down, and 3d printed aesthetics on each leg.

quick render to show magazine placement:

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#3 ·
What mags are you going to use?
 
#6 ·
My bondo skills and expanding foam skill will tackle that stock shape. then faux wood grain. you can see the abs reinforcement under the stock plastic welded.

the upper receiver is 3d printed and the side magwell is the rectangle on the right. the hopup needed(not really) a channel to slide into the front of the receiver. i found that out later lol

the lower receiver is smoothened out and by now is already painted

the 90 deg hopup i rock solid and squared. the grip is painted and about to get faux wood grain. the coarse grit sander put in some nice wood texture to boot. nice! ill do the same to the stock.

Wood Air gun Trigger Gun accessory Gun barrel

a lot done the firt weekend.

next weekend i plan to get the magwell welded to the body and test feeding/locking in the hopup. also: finish contouring/painting the stock, printing the rest of the front end and final shaping.

last week will be: recreating the front bipod which locks fore and back.
 
#7 ·
I want this build to feel finished and look good from the inside out. It will be able to be stripped down with a removable stock, and also be painted on the inside. it will take a keen eye to spot the hand made parts. also, I like to flex everything while im making the body work to see if things crack or snap ( and they do ) so i can make it stronger than prior.
 
#8 ·
mock up, and magwell centering. oh the sweet sweet smell of bondo stuck in my nose. magwell is a little tight.

now how to adjust hopup? i left the opposite side solid LOL. I will make a door which will look like the charging hook of the real FG!

the front end will take a whole weekend to design peices for. its coming together quickly and nicely imo

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#13 ·
heres an update 2 weeks in...

first layer of bondo roughly sanded but i can see a few low spots. will do one more serious layer, then should just be just spot putty after that.

that hole on the side is to adjust the hop up, ability to uninstall the hop chamber (90 degree), faux charging handle, and adds rigidity. quad purpose! i WAS going to add a spring return door.. but the client isnt paying NEAR that amount for fabrication. i could literally stop right now lol/

making a robust barrel with a bipod is a challenge in itself when that bridge comes..

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#14 ·
You've got a lot of room in that receiver to reinforce the barrel, let the outer barrel extend into the receiver and use some metal reinforcement inside it to stabilize the exposed barrel.

The SAWs and PIGs are set up like that. There's a block the barrel sits in and there's a reinforcement point at the front. Those provide the strength to support the bipod.
 
#15 ·
I got some thin steel pipe, but the OD may be too big. I'm thinking putting a torch to the pipe end and just melting the pipe into the receiver. Then reinforcing more on the outside.

Also note the inner barrel is centered on the receiver. The fg has the barrel more top justified. So I'm most likely going to make the inner barrel offset in the outer barrel.
 
#17 ·
Melting it into place may not be the best idea. Remember, as the pipe melts into the plastic, the plastic will keep pulling away from the heat source. In other words, you may end up with a bigger hole than intended. If it was me, I'd drill it out with a spade bit or a forstner bit. Drill it undersized if you have to and sand or file it to the desired size.

Just something to consider.
 
#18 ·
def appreciate the tips. i understand what you mean. Im scratching melting the pipe into the print. the print is hollow and i may do more damage internally.

my plan is to make the barrel removable with a set screw. here is my plan for the bipod mech using those pipes and a bolt. (also note how the inner barrel is low on the bore)

15 degrees on each leg. the purple cylinder is the OD of the outer barrel

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#23 ·
pretty much 90% done.... needs iron sights, set screw for barrel, wood grain and clear coat.... takes down into 3 peices. barrel assembly, upper receiver, stock and lower. the stock can be removed but pretty much the length of the barrel assembly. the barrel inserts a good 4 inches into that front peice. 1.5" of that is into the receiver.

the bipod feet lock up folded onto the main barrel. (similare to the RS but not quite)

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#24 ·
flip iron sight fabbed up. kept it simple. I will drill through to make a joint. then use pla filament to rivet both parts. the square nature of the joint will create a auto locking folded down and folded up feature. may need to sand/round corners slightly.

also faux bakelite/wood grain is in the booth drying... more pics to come.

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#28 ·
Used the stock jg metal v1 hop unit. Chopped it and rotated.

So it feeds great.

Now the problem is I'm getting 90 fps. Lol

Smh

The magwell is off by 1mm. Causing nozzle to rubber airleak.... I could:

Add material to the nozzle.

Move the retaining pins back.

Lastly I could cut the magwell off and shift it backwards.
 
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