Picked up two uppers and some other parts but don't know what I have. I knew they were different so of course I had to buy them. Some kind  of trainer? Bores sleeved with plastic about .375 id. Modified charging handles. Oddball hammer. Burst mechanism trigger assy. No gas tubes.

Just based on design, I have a feeling it's something like a prop propane gun.

The design of the hammer would require removing a substantial chunk of material from the lower between the hammer and magazine well, as well as removing the bolt catch (or at the very least grinding off it's trip leg rendering it inoperable). It also has a new contact anvil added at an almost 90º to the original contact surface. To me, this indicates that there was a valve in the mag well area that fed the action of the cycling instead of ammunition of some type.

Hopefully someone will come along who knows for sure, but If I had to take a guess, I'd imagine it was a prop gun that had a propane tube fed down the bore to the muzzle and the sleeve kept it aligned - probably why the front of the upper was ground because there wasn't enough clearance for everything to fit and they need the extra space. The magazine contained a small tank or the mag well area had a connection with a small hose to an off gun tank. I'm going to go on a limb and guess that the bolt is spring loaded but depresses very easily - the gun 'fires' and back pressure compresses the bolt to the rear of the upper, the small tail remanent of the hammer is caught, pulling it back as well, which closes the valve and cocks the weapon. With pressure removed, spring tension returns the bolt and the process can begin again. Looks externally like the real thing, because it is, but instead of shooting lead it's throwing small fireballs.

That's my guess, but I'm no expert.

Does that rod/piston thing insert into the upper? in place of a bolt carrier? That might be a paintball or dart/tranquilizer upper. The Armalite windage knob is the coolest part

The rod/piston thing is the buffer. Has a standard rifle spring. One upper is Colt, the other is Armalite. I have already stripped all the useable parts. Lots of goodies. Not sure yet if the uppers will be usable since there was some milling done.

My guess would be an air gun like the ones used in the EST simulators.

Are there any ports cut in the barrel? The SAT range rifles we used to use had a hose fitted into the bottom of the barrel.

No ports cut in the barrel.

Before the EST 2000 simulator / trainer there was MACS.  MACS used a Nintendo console and a laser that attached to the end users rifle barrel. Before MACS there was Weaponneer. Weaponeer wasa  mostly mechanical system like arcade games before video. The rifle portion of Weaponeer trainers were made using highly modified M16 rifles and some specialty parts. They had a steel actuation rod of about 3/8ths inch diameter that ran up the bore.  I'd look towards Weaponeer as a possibility.

I got to fire a weaponeer as a kid.  It was awesome.  Would make an awesome pin ball type game for a basement.  It also had a scoring system on a second computer print out . I was 12 and managed to begin hitting the targets after a small amount of instruction . I cant offer any help on what your rifle is but if its a weaponeer system I hope you build the whole thing.  I remember it had a landing deck to lay on or kneel and sand bags to rest.
 

Thread from here in archives

I think it would be tough to find the parts to complete a simulator although it would be pretty cool so I'll just use the parts for two more builds. The other parts are Colt 603 so that's what I'll do with that one. The Armalite stuff will go to a generic shooter.