"This piston head is awesome. Like a check valve it lets air in from behind the piston head to gather in front of if when being pulled back by the gears. Then blocking the air and effectively pushing it forward when released by the gears.
Its aluminum construction is really nice and durable and wont crack like most of the plastic ones eventually do. I do advice to use it with a high quality piston that wont crack, like the red "Lonex Ultimate Upgrade M170 Polycarbonate Piston".
Since this is alu, and not plastic, it should only be used with a 100% stainless steel cylinder, the cheapest models will do fine, but you may have to polish its inside, back on that later.
Why Stainless Steel Cylinder? Because its hard. Brass and Aluminum cylinders are soft metals and you really don't want two soft metals rubbing against each other, especially not Alu against Alu.
Make sure the stainless cylinder you pick is without any fancy "special inside coating" that can be grind of by the alu head grinding against it, those coated cylinders work better with plastic piston heads.
Now make sure the inside of the stainless cylinder is polished to a complete mirror shine. You must not be able to feel any ribbing on the inside walls, or it will slowly grind away alu from the piston head and rubber from the O Ring. You can polish the inside of the cylinder by wrapping a 2500 emery cloth (made for polishing steel) around your finger and polish it, in a lengthwise motion, for about 15-20min then moving up to a 3500 emery cloth for 30-40min then a 5000, then finish it off with a polishing paste for steel. Or use a Dremel with a polishing head and grinding paste. This will take time, but its worth it.
Make sure you clean it thoroughly afterwards with dish soap leaving no residue what so ever.
The ball bearings of this piston head is also of a nice quality as well. And the "shock absorbing" front rubber is really nice and dampens the blow to the back of the cylinder head nicely.
For best operation make sure you use a cylinder head that allows for such a pointy piston head tip to "enter" at the back. Like the backside of the "APS Cylinder Head" or the backside of the "ASG Aluminum Cylinder Head" for example.
The only downside of this piston head is that the orange paint will come off with usage and will mix with the cylinder grease to create a grinding paste "harmful" for the O ring and the polish of the cylinder. You can always polish the orange paint away before using it, by first removing the O ring and front rubber, then polish the widest (and largest) of the orange alu sides on a polishing wheel to a mirror shine. Clean it thoroughly, especially the small holes, and then reset the rubbers. Make sure you glue the front rubber with a super glue so that it doesn't come off when firing. Its quite simple to attach it correctly, don't worry.
After this operation it should have a completely smooth play inside the polished cylinder even without grease. That's when you know you've made it perfect. When grease is later added it works like a piece of German machinery.
Take notice to only use 100% pure silicone grease when greasing the inside of the cylinder as any oil containing even 1% Petroleum will deteriorate the rubbers and plastic of your airsoft. DON'T trust the different Chinese "Airsoft greases" since they most likely have been diluted with petroleum and/or other substances harmful to rubber and plastics. Go instead to a hardware store and search for 100% pure silicone grease. Should be found at the plumbing section. If it doesn't say 100% silicone, ask someone who works there to check it or find one for you.
This, 100% silicone grease only, goes for all the rubber parts and mechanical parts of your gun. But especially on the parts inside the cylinder since small grease particles may or will eventually be shot thru the cylinder head and into the barrel, and perhaps sligtly grease your hop up rubber that should not be greased at all because it looses it hop-up effect when greased. If it is greased with silicone with petroleum in it, however, it will also start deteriorating thus lowering you precision and accuracy.
Yes, all of this is on a very nerdy level of perfection right now, but if you don't care about these things you would not even be looking at a piston head like this... or any upgrade parts for that matter.
Anyhow, buy this piston head, its awesome. Of course you can use it just fine without all the fine tuning I've written about. But your machine will preform allot better and last allot longer if you do them.
Praise the Omnissiah and Happy airsofting.