So just what is the difference basicaly, between the M1 carbine and M14 rifle gas systems?

The carbine is supposidly a 'tappet system' and an M14 a 'gas piston' style. Both would appear to me to use a gas piston to get an action-bar to unlock a bolt, etc, etc.

My pal swears they are "completely different operating pricipals....Carbine Williams.....blah, blah....gas tappet...blah blah. Totaly different from the M14, which uses a piston....blah, blah, blah"

Not saying he's wrong, just saying that a 'tappet 'equates to a 'piston' operated system to me.

So what is the theoretical difference between the carbine's tappet, and the M14 rifle's gas piston if any?

Thanx, Seventeen!