AEG Piston Rack Short Stroke Service

This service must be purchased alongside a piston purchased from Northmark Vault.

This service is for those who don't have the proper equipment, the time, or for techs who are looking for a high degree of accuracy when it comes to removing teeth from a piston rack.

Service Details

• Pricing: $8.00 per piston
• Tooth Removal Process: High-quality machining process using a carbide end mill.
• Quantity: This service only covers 1 piston. If multiple pistons need this modification, please purchase the same amount of quantity of this service. Example: 1 Piston = 1 service. 2 Pistons = 2 of this service.
• Turnaround Time: 24-72 hours of purchase, Monday- Friday. Holidays not included.

Why Short Stroking?

Short stroking is done for a few reasons. The first and most common reason is to prevent premature engagement (PME). The most common occurrence of PME happens when running high cycle rates. The gears can cycle faster than the piston is moving forward, causing the piston to be engaged before it is completely forward. This can cause inconsistencies in FPS, low FPS, and in the worst cases, damage to the piston and/or sector gear.

Another reason to short stroke is to adjust the cylinder-to-barrel air volume ratio. Without getting too in-depth into air volume ratios, the average agreed-upon ratio is between 2.0:1 and 2.5:1. There are many calculators online that can help determine your air volume ratio.

Another, more time-consuming but similarly effective way to approach how many teeth need to be removed is by firing your replica through a chronograph using the ammo, spring, barrel, and all other components you plan to run together. If you have joule creep (i.e., your replica produces higher joules with a heavier BB than it did with a lighter BB), you have room to remove teeth and correct the air volume.

With that being said, air volume adjustments are also commonly achieved by selecting different cylinder porting. The reason myself and many other techs prefer full cylinders and short stroking to adjust air volume is because it removes unneeded energy during cycling. This means there is no wasted air being vented out, and it also helps prevent premature engagement of the piston.

Another added benefit of short stroking is an increase in cycle time and trigger response, due to fewer teeth engaging and the piston being released earlier in the cycle.

Teeth removed during short stroking are always taken from the release side of the piston rack.

AOE Correction

AOE correction is only performed on specific pistons, typically stock pistons or more budget piston options on the market. Most higher-end pistons already have AOE correction from the factory.

In the rare case that they do not, this modification must be performed to account for the piston rack and body being spaced further to the rear of the gearbox. The typical modification involves removing the second tooth from the pickup side, and sometimes removing half of the third tooth. This compensates for the change in angle of engagement created by spacing the piston rearward.

How Northmark Vault Performs It

Here at Northmark Vault, we believe in a high degree of accuracy and repeatability when it comes to modifications such as short stroking.

For that reason alone, we do not remove teeth by hand using a Dremel. Instead, we remove teeth accurately and cleanly using a carbide end mill, which produces a smooth, precise, machined finish.