The inner workings of a high-cap magazine

[Flenix]

Hey guys, me again!

 

I'm in the preliminary stages of planning out a technology aspect I want to implement into my guns; in the form of a HUD mounted with useful information - one piece of that of course being my current ammo.

 

Now, for low-cap (standard) mags, this is pretty easy. Fill it up to capacity, shoot away, and when you reload it breaks the metal contacts and "resets" the counter back to full.

However, obviously with high-cap mags, this isn't as simple, because you don't remove the mag to reload as often, you just wind away at that noisy little wheel on the bottom. (Seriously, you might as well just shout RELOADING at the enemy.)

 

I figured there must be a way I can get around this, so opened up a cheap Cyma high-cap I got with my 25 quid spare two-tone G36. This, is where I'm stumped.

 

The internal assembly seems relatively simple; the BBs sit in a hopper on top of the wheel, and when it's turned the wheel acts as a conveyor and pushes the BBs around, and then up the feed into the gun.

However, when the feed tube is filled up all the way and tight (meaning the BBs will push up without the help of gravity), the wheel stops feeding in new BBs. Even if there's room for them to move around the wheel towards the feed tube, they just stay where they are. There's a second cog in there too, which also stops moving.

 

My mag is plastic. It's a very dark translucent plastic, I can see through parts, but not the cogs - Does anyone have any idea what kind of little mechanical switch is going on in there to say "OK, I'm full now, stop giving me BBs"? - I'm hoping I can use that to tell my system there's currently a 31-BB mag installed, and have my connection switch on the wheel so when it's turned, the counter is reset.

That's a bit of a rambling post; I can get some pictures if that helps anyone?

 

TL;DR - How does a high-cap mag know when to stop feeding BBs?

[Samurai]

There is a coiled spring that turns that wheel. You wind up the spring by turning the other wheel at the bottom of the mag. (Yes, those are 2 wheels on one axis). When there is no more room to push the BBs up, they don't get pushed up. When some room frees up (you shoot), the spring turns the wheel some more to feed new BBs. When there spring fully unwinds, it won't feed the BBs, you need to wind it again.

[Ian_Gere]

You might want to consider a microphone connected to your timer circuit to count shots fired.