This is why full metal pistons are not the greatest thing ever

[ThunderCactus]

Metal racks usually only fail on the first tooth where the most mechanical shock happens, that's why all the GOOD pistons are POM or nylon with 3-7 metal teeth (depending on FPS). Metal is highly wear resistant making it the best material for the sector gear to slip off of.

This particular piston was engineered to break, there's no other way to put it.
The rack has no bottom land between teeth, they simply V together creating easy shear points.


Hardened metal is inherently brittle, meaning it's not good at absorbing mechanical shock, but excellent against mechanical wear.
Nylon is soft, and slightly elastic, meaning it absorbs impact and springs back to it's original shape.
POM isn't quite so elastic, but is much harder, and brittle like hardened steel. But POM pistons are engineered with reinforcement (the bar across one or both sides of the rack) allowing it to take higher stresses.

[audi_bhoy]

I've had a customer bringing me his M4 as well, he told me it wouldn't cycle. I could hear the motor clicking when trying to fire. Upon disassembly, found a lightweight aluminium piston jammed one the gear, half ripped. I tell customers it's better to replace a polycarbonate piston after a jam than a gearset, faster to change and no shimming job...

[Kokanee]

Ever since I started working on my own AEGs back about 2004ish, after dabbling in after market pistons I started just buying up stock TM pistons and those are what I use as replacements. I've owned a number of CA AEGs and I always take the stock piston out and throw a TM one in...In fact the piston in my CA AK74 has been installed since 2006 and is still going strong.

[Styrak]

Pretty poor picture, I can't see what's going on there.

[ThunderCactus]

and THAT is why blackberry is going under.

Yes I know it's a crap picture, but the first tooth of the rack has migrated to just below the sector gear where I'm pointing

[iKliiu]

Did you epoxy the rack in and correct AOE?

[Cobrajr122]

Originally Posted by iKliiu

Did you epoxy the rack in and correct AOE?

That sounds like a horrible idea.

I dont see epoxy being stronger than a new piston...

[Spike]

I think he meant epoxy the rack in when the piston was first installed.

Though I'm sure this was not TCs gun.

[lurkingknight]

full aluminum pistons will shear the pickup or the entire rear of the piston off... just way too brittle... but properly prepared full metal rack on a nylon fiber body will probably outlast anything out there. 3-4 metal teeth pistons are best if you want to lower the weight up the setup more... you can get a super feather weight piston assembly by swiss cheesing a halfrack piston.