Shell Ejecting Rifle Mechanism

hey, I am back! there are a lot of Lego guns which shell eject and even shoot too, but always the shells are monstrous at a 3x3 cross-section, and the guns tend to be 5 wide. Well, I designed a shell ejection mechanism in only 3 studs wide(with walls) with 1x1 shells. It is cheaper and easier to build than other alternatives.

This mechanism took me a week of work to design. First I found the perfect extractor-shell combination(twice), and then made the bolt and mag assemblies. The biggest hurdle was that I needed the rounds to pop right into the bolt extractor, and not in front of it(the extractor is rigidly connected to the bolt, so it can’t move out the way to grab a round face-on)

this particular iteration doesn’t have a dedicated ejector, and instead ejects with the ammo inside the mag!(or the pusher if it’s the last round)i think that’s genius

this is as much a tutorial as it is a documentation for the mech if I would want rebuild it later.

WARNING: this is designed to throw spiky Lego into your eyes. Wear glasses or smth, be warned

1 rubber band, and a lot of Lego and patience

a quick glossary of terms I use:

extractor-is at the end of the bolt normally(mine is atleast). It grabs the shell and makes it follow the bolt. Also allows for ejection ion tandem with the ejector

ejector-a piece which blocks the bottom of the shell, so that the extractor starts rotating the shell instead of translating, making it eject. My design doesn’t have that, since the next shell in the mag(or the pusher) fills that role.

bolt- a stick which moves back and forward in the gun, either manually(like mine) or automatically. The bolt pushes shells out of the mag, into the chamber, and backwards for ejection. I think most guns have that.

chamber-irl where the ammo is detonated. In my gun, it is the place in front of the mag where a shell is put when the bolt is full forwards. This allows the next shell(or pusher) to pop.up a bit to act as the ejector.

pusher-the thing which pushes ammo from the mag into the gun.

receiver-the place where the mechanism is I think

I went thru 2 iterations of the ammo: a round ,sturdy design first, and then a flat cheaper design. The current version only works with the flat design(round ones jammed because of some grooves on the pieces(the cone on in particular). The flat design has 3 interchangeable variants, depending on what you have most of

That triangle piece is the extractor. The flat shell design actually has the same piece to latch on to the bolt, while the other created a circular deep groove for locking.

here I show how to build the bolt layer by layer

Where the bolt&shells slide around. I also include the rail and stopper for the bolt.

for the latter I put 1 photo, which should be enough. For the former, I will take the same layer-by-layer method from earlier

Not much explaining to do here

Make sure the floor is flat, so no jams occur later

It is probably the worst part if the design, so feel free to try to make a better one(and tell me pls too). It holds 3 rounds before the rubberband’s tension gets so high it starts jamming everything. Note that I use a rubber band which got stretched quite a bit before, so you might want to do smth with yours.

also I use the same layer-by layer thing, but the layers are thrice as tall

The images are sufficient to build the piece. This piece is the only one in the whole thing which is more than 3 studs wide. You will have to live with that. Again, layer by layer

the roof must be pressed completely into the chamber/receiver walls when assembled, to apply pressure on the bolt, so it ejects shells instead of just jumping and leaving them in the chamber, jamming the mechanism

to be sure, the roof is just 5 2x3 tiles in a row, with 2 1x8 bricks and 1 1x6 brick to prevent flexing

In pic 1, are all the pieces needed here. In the rubber band, you have additional pieces not discussed in previous steps.

when putting the mag on, make sure to align it with the hole, or else the ammo won’t pass.

If it fails to eject, there can be 3 reasons: the rubber band, the roof, or the ammo. The band could be too strong, or the roof could’ve come off a little and stopped applying pressure to the bolt, or the ammo is wrong. I suggest then to make more ammo until it works. Of my 11 shells, only 3 are reliable an can be loaded at the same time.

So here you have your shell ejecting “gun”! You can cycle it pretty fast too.note:you can load the shells by removing the mag pusher and putting them in the mag(close the bolt first so the shells don’t fall out, or you can load it thru the chamber, without disassembling anything(I let you figure that out yourself)(ask if you want an explanation on that)

note2: change the bolt handle if it jams on the white stopper piece. Remove everything except the reed piece which is inside the bolt, and then put another handle to your liking there.

i would’ve thrilled to see you add stuff to the design(like a new mag), or even make an actual gun-looking thingy around the mechanism.

if you do, pls tell I wanna see.

have a good day, from me and scarecrow the hamster.(scarecrow is his name)