Let's talk about Pistons

A lot of you are wondering: "What piston should I buy? Full metal rack? Half-rack? Does material matter? How many teeth?"

Full metal rack vs. Not-full metal rack

There are 2 camps on this. One is that a full metal rack trumps all because it’s 1 piece and the pickup tooth is less likely to shear from each other. However, the caveat of that is that the integrity of the piston suffers because the majority of the force still has to come back into the piston body, and the contact area between the metal rack and the plastic body is not a lot. We see failures on these pistons from the rack simply getting torn out of the piston body. This can be easily remedied by applying a layer of superglue along the rail on which the rack sits - transferring the impact forces directly to the body of the piston.

Another failure point of full-metal rack pistons is the at the pickup tooth where the underlying plastic basically disintegrates but the metal staying intact. Also, having a full steel rack means that you may wear down your gears faster. Replacing a piston might be cheaper and less time consuming than replacing an entire gearset. A huge advantage of steel rack pistons is that they almost never suffer a pickup tooth failure (ie: steel tooth separating itself from the rack).

The other camp is that you want as much plastic as possible so that it forms a generally larger 1-piece mass that can absorb and dissipate the impact energies better. However, that means that the pickup tooth will have to made out of the same material as the piston, which could be quite weak. Almost all plastic pistons' failures come from the pick-up tooth breaking off the piston body. Special considerations must be made regarding the material used in this application to have the right balance of rigidity and elasticity.
We actually used to run stock Marui pistons for a long time because they had this special blend of fiberglass and plastic that made them quite strong but the release tooth was made out of some shitty pot-metal that didn’t hold up well once you went past 400fps as the sector gear slowly grinds it away. The Lonex example is probably one of the most well-designed pistons we've seen - the material composition as well as the thickness of the piston lends itself to be one of the most durable pistons we've used. We've run M140 springs against it with 16:1 gears without failure. The only other 2 pistons that *might* be better than the Lonex, are the Supercore Pistons and Prometheus Hard, both of which are $40+. Structurally the Lonex is almost identical to both these pistons. The reason why Lonex has added more metal teeth towards the release tooth is for those short-stroking fiends who are removing a ton of teeth off their sector gear and would like to remove a corresponding amount on the piston body. Also we presume another reason is to distribute the shear forces exerted by the release tooth when the piston begins its forward stroke along more metal teeth.

Polycarb? Plastic? Fiberglass? Aluminum?

A lot of marketing gimmick has led some players and techs to believe that polycarbonate is the material to use for pistons. We cannot stress enough that this is probably the worst material one can use, aside from aluminum. You'll hear a lot about how polycarbonate is used in bullet-proof and ballistic glass, etc, but thinking through this - what happens to these materials upon impact? They crack. So why would you want a material that's known to crack in your piston?

Aluminum pistons are probably just as bad as polycarbonate due to the fact that they basically absorb very little energy upon impact. However due to the increased overall weight of aluminum vs. plastic, manufacturers have to swiss cheese them and lighten them in every possible way, leading to reduced strength. Coupled with the fact that most aluminum pistons are most certainly cast and prone to "bubbles", they will not handle shear and impact forces well. 90% of failures on aluminum pistons occur on the pickup tooth from it simply not being able to withstand these forces.

So this brings us to glass-filled nylon pistons and fiberglass pistons. Surprisingly enough, softer pistons actually last longer simply because they are able to absorb impacts and have an element of elasticity to them that makes them ideal to be used for pistons. They are also able to distribute energy throughout its structure quite well and are extremely easy to work with (dremeling the 2nd tooth to correct AoE).

Conclusion

With any piston, you should correct your angle of engagement, either via washers on the piston head or with a sorbo pad on the cylinder head. But ultimately the piston should be considered a wear item and it should expect to be replaced at some point in time.