I'm new to the AR scene and was thinking of a poor-man's piston mod for an AR.  Would it harm the rifle to manufacture a piston that would fit in the stock (or maybe little enlarged depending how much money I can muster) gas tube and have it thread onto the carrier key?  Since pulling the charging handle unlocks the bolt and cycles the rifle normally then wouldn't this mod work?  Im thinking either that or get a modified carrier key with a piston integrated into it.

Any comments or suggestions are appreciated.

I don't have nearly the cash to buy a piston upgrade kit so don't bother saying "Just get a piston upgrade kit."  All that will earn you is a "dumbass."

Thanks

Where can I get a Piston upgrade kit?
I think what you are trying to do is called "R&D", which manafactures spend thousands on.
It might be cheaper to buy an upgrade kit.
so I repeat:
Where can I get a piston upgrade kit?
check6
Danomite

I'm convinced! How about not buying a kit, or parts for a home-brew design & saving yourself a lot of $$...... and showing the good sense not to f-up a perfectly good weapon. Buy some more ammo, a barrel or optic with the dough you saved?

JMHO,

Hotgun

Danomite-  Patriot Ordinance Factory has a piston "Spare Parts Kit" which has everything except the special thing to replace the carrier key with and the special gas block for $150.  It's a fairly slim system and should work with any normal AR handguards but I might be wrong.  If worse-comes-to-worse, you can always buy the Predator handguard they offer and be guaranteed of a good fit.  But if you go that route I would just build a piston rifle.  Erm disregard the last sentence, it was the BRD speaking.