Making Your Own Custom Piston.
Like a lot of builders, I am not blessed with a fully equipped machine shop.
These modifications are done with basic tools.
AK pistons have a hard chrome plating to help protect against the effects of corrosive ammo.
After many attempts to drill, I found heating the piston and shaft with a MAPP torch to a cherry red, and then air cool, will allow drill bits to work better. This heating will not affect the hard chrome plating.
Most pistons have a divet on the top. Center punch piston dead center. Use a drill press and a machinist vice, and make absolutely sure the piston is parallel with bit.
Drill with 1/8" drill bit as deep as the piston is long, and add an additional 3/16". Go slow and use oil.
Piston drilled. (1/8' bit) Leave piston in vice.
Now use a 5/16" bit and drill slowly and use plenty of oil. Piston drilled with 5/16" bit.
Piston drilled and cut off shaft.
Notice piston was drilled dead center. A MUST!!!!
Cut shaft to needed overall length. This will be the total OAL of the piston Top of the shaft will be flush with the top of piston.
Bevel the top end of the shaft so the piston will start slightly. Make sure the piston is square to the shaft. Lube the shaft with oil or grease. Set the two pieces in a press, and slowly begin to push, checking at all times that it is not binding.
After pressing, I drill through the piston and shaft with a 1/8" bit. I then pin the piston to the shaft with a 1/8" tension pin (roll pin). Piston is now done.