Some notes to clarify misconceptions based on my personal observations from modifying AEGs:
Aftermarket piston heads with bearings:
The bearings will only serve to add FPS *IF* you are comparing to a piston head without bearings OR any type of large spacer/locknut used to hold the piston head in place (Tokyo Marui is NOT one of these as it uses a large diameter and thick nut to lock the piston head in place.)
When comparing a systema silicone piston head with bearings to a setup using a Tokyo Marui piston head with the stock nut to hold the piston head in place, the Systema piston head actually showed a 7* fps reduction.
However, when comparing the Systema piston head with bearings to the Systema piston head WITHOUT bearings, the bearing setup showed a 15* fps improvement.
The Tokyo Marui piston head, showed a 22* fps improvement over the Systema piston head with no bearings.
The reason for this is simply due to the fact that the bearings typically found on both Systema and Guarder piston heads are physically shorter than the Tokyo Marui nut which holds the stock spring and piston head in place. Therefore, the Marui nut compresses the spring more than bearings will.
As Skruface's article points out though, velocity is not "the key" to having a more accurate gun. CONSISTENCY is the key and this is one of the main benefits of aftermarket piston heads. Chronograph tests show aftermarket piston heads put out more consistent velocity in shots than the Marui one does.
*These tests were performed with a PDI 120% spring. As your spring gets stronger, so will the velocity improvements, meaning at 400 fps, a bearing part will give a 25fps improvement rather than 15fps. Likewise, the weaker your spring is, the lesser your velocity gains from a bearing part.
"Economy" and "Reinforced" pistons:
The Economy pistons do not have a plastic final tooth as stated in the article. In fact, there is no final tooth at all. The only thing there is the slot which allows you to remove the final steel tooth from your worn down piston and slide it into the "economy" piston. So basically, you save a couple of dollars for a part that you already have and don't need to buy again.
Pistons are consumable products. Out of all gearbox parts, the piston is probably the one that goes through the most wear due to the fact that the material is typically the softest material found in the gearbox and the gear rack goes through a lot of wear against harder materials.
So the "economy" version is just a replacement for a consumable product at the absolute cheapest cost. The material is exactly the same as the "other" piston.
SystemA's Red Piston:
The slot for the final metal tooth is about 0.3mm too far
forward, not backward as stated in the article.
This problem, however, has been fixed. All SystemA Red Pistons have no problems now.
Helical Gear Sets:
Re-iterated from this thread:
http://www.ascforums.com/viewtopic.php?t=18629
I have heard many different sources make the common misconception of half-tooth pistons being required for helical gearsets.
The truth is, ALL gear sets, helical or not, use full-tooth pistons EXCEPT the Super Torque Up, Ultra Torque Up and Infinity Torque Up Gear sets.
ALL gear sets have a flat sector-to-piston tooth interface.
The *only* helicoid cogs are the bevel gear to spur gear connection and sometimes on the spur gear to sector gear connection.
Everything else is flat.
This common misconception may come from the fact that the Ultra Torque Up and Infinity Torque Up gear sets come ONLY in helical gear formats. (Although the Super Torque Up comes in both flat and helical versions)
The reason why the Super, Ultra and Infinity gears need a half-tooth are because the cog which connects the sector gear to the spur gear is much larger in diameter than lower torque levels - so large, that it's diameter is actually as large as the diameter across the sectored teeth. This larger diameter is required in order to get a high enough tooth count to get the added torque for very heavy springs.
This is a photo of a HELICAL Torque-Up set:
Notice how from this view, the sector gear (top-right gear) looks like a flat tooth sector gear? None of the teeth on that rack are helical. Not slanted. They are full teeth.
Now this is a photo of an Ultra Torque Up gear set:
Notice how from this view, the sector gear (top-left gear) has a full rack of teeth and appears to have no sectored teeth?
Although the sector gear of Super, Ultra and Infinity gear sets look like it has a full rack of teeth around the entire circumference, there is actually a sectored rack of teeth. The rest of the teeth have half cut away and can be seen if you look at the side profile of a Super, Ultra or Infinity gear set. The full gear rack around the circumference is the interface with the spur gear. I hope that clears things up.
To summarize: Half-Tooth Pistons are only required for the Super Torque Up, Ultra Torque Up and Infinity Torque Up gear sets. *ALL* other gear sets besides the two above-mentioned gear sets can use normal pistons. To clarify, these following gear sets can use standard full-tooth gear sets, regardless of whether the gear set is helical or not: High Speed, Standard and Torque Up.
Top Power Springs:
Am I correct in assuming Skruface's referral of the
Top Power 170% spring which dropped from 423fps to 400fps in one day to be what he saw happening to my P90 at Operation: Capital Thunder 2 after I blew off 5 hicaps to "weaken the spring?
I believed that the firing of the rounds were the cause of my spring to drop in fps.
That was until I got my own chronograph and realized that the drop in FPS was not due to a softer and more malleable spring material... it was because my initial field chrony tests were performed with my hop up off which yielded 436 fps. But while blowing off the 5 hicaps in an attempt to "compress the spring", I had adjusted the hop-up for that day. My final attempt at the chrony station yielded 406-409fps with the hop-up on.
I can duplicate this effect and can yield similar velocities, even though it has been over one year since that event.
On another interesting note: In a comparison of springs rated to output similar velocities (Top Power 170%, PDI 150%, Systema M120, Guarder SP110), Top Power yielded THE MOST CONSISTENT velocities, followed by Guarder, then Systema and finally PDI trailing the pack.
Bushing Compatibility With Certain Gear Sets
I have also heard that there are particular compatibility issues regarding Guarder dual oil channel bushings with SystemA reinforced gear sets. However, I have not had this problem with four different SystemA reinforced gear sets (Standard Flat, Torque Up Helical, Ultra Torque Up Helical, Infinity Torque Up Helical) and three different sets of Guarder dual oil channel bushings.
I hope all the information provided in this entire thread proves helpful. I've also been meaning to put all the data I've gathered into a guide, but I'm just too lazy to get it started. I'm just adding on to Skruface's work right now, so I'd like to thank Skruface for putting the effort into getting up a well written and concise upgrade guide. This is a great start to getting all that information that everybody has wondered about into one convenient location.