As seen in “Special Weapons for Military and Police”

This outstanding modification that puts my AR15 to shame.

It was built by Kurt’s Kustom Firearms and is is the KKF exclusive piston/pushrod gas system (patent pending) that replaces the standard direct-impingement gas tube system for the AR15 and M16 family of weapons:

Starting with a block of billet steel, I machine the gas block:

In the rear of the block, a SS piston is installed:

then the piston cup:

A titanium intermediate oprod seats in the back of the cup, and mates with a hardened 17- SS rear oprod:

A KKF carrier key from properly hardened O1 tool steel:

replaces the standard carrier key and accepts the rear of the rear oprod.
Upon firing, gas is bled off the barrel’s bore through the gas block and into the piston, which forces the piston cup to the rear along with the titanium intermediate oprod and rear oprod, cycling the weapon. By changing the length of the titanium intemediate oprod, differing gas system lengths are achieved, shown here on a midlength gas system carbine:

I have many different products for the AR15/M16 family of weapons, and much of the material for them comes from OnlineMetals.