Any ideas? I'm about 90% sure what it is.
It is fitted into an object for use with the M16A1 rifle.

It looks like some kind of steam-punk hard drive.

ok here goes!
After lots of studying the photo. Im going to say it some sort of dry firing device.
It some how throws the bolt back far enough to cock the hammer so you don't have to use the charging handle every time.
IDK WTF it is LOL Ha Ha

Fits into magazine, possibly something to with depth and or resistance necessary for the bolt to strip a round from magazine and send into battery?

It fits in the magazine well, & locks the bolt open after a revolution.  What is that, 30 teeth?

TAG

It looks like the "gear" is turned every time the bolt is cycled into battery.

Does this thing somehow cycle the bolt for dry firing or something??  LoL

Does it go INSIDE a magazine body?

That last picture looks like it has the same profile as a "lightning link". Hmmmm

 

Based on design alone - a 30 round magazine simulator for a firing device that doesn't use ammunition.

It's in the "empty" position now. I assume it slides into a magazine body and is locked into position with the spring loaded pin seen at the bottom of picture 3 as well as the lower left hand side of picture 1. The assembly on the top of picture one seen in picture 5 is a ratcheting assembly that advances the gear each time the bolt is cycled, probably from something like a propane prop gun or a laser training system with a pneumatic recoil simulating bolt. Once the gear is ratcheted enough, the plate in front of the gear raises the spring loaded arm on he right of picture 1, left of the picture 2, and center of picture 4 to trip the bolt catch simulating an empty weapon and allow for realistic magazine changes. Without looking at it more closely, I think the arm on the top left of picture 1 and the top of picture three is used to reset the device, probably with a reverse ratcheting action so you can set capacity for 20 or 30 round magazines. You can also tell the gear is spring loaded with something like a clockwork spring because you can see the bent tail that is holding tension on the gear at the ~ 7:30 position of the gear in picture 1.

That's my guess at least.

Magazine insert, full auto dry fire mechanism

looks like a winner.
I believe this is the 1 to 30 round adjustable magazine for the weaponeer training system. They have a fixed 20 round mag and a fixed 30 round mag and I believe this is the 1-30 round adjustable magazine. I've been unable to find any photos of this magazine in any manuals on the internet.

I thought it was a baseball card in the spokes simulator, the faster you pull the charge handle the more noise it made.

Weaponeer:

http://weaponsman.com/?p=36354

http://www.thefirearmblog.com/blog/2016/11/08/weaponeer-us-army-rifle-simulator-bygone-era/

I think this is Weaponeer related as well. It came with a modified barreled upper and buffer.