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PDI VSR-10 upgrade parts
A vacuum (VC) piston is closed when going forward, but opens up to prevent negative pressure in a long inner barrel.
Benefit of the V-trigger displayed graphically. The piston is not pushed upwards, so the start position is more stable with high power springs.
Some PDI parts for the VSR-10 laid out. Spot the ultra-lightweight Barikaru piston, Palsonite cylinder and super-hard piston among others.

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Probably the first thing you would choose is the spring, so let's start here. PDI springs are hand-made from silicon chrome steel alloy, which is the same material as used in train and truck suspension springs. The high grade material and correct heat-treating process make the springs last for a long time with a stable output. There are two VSR-specific spring types available, and a general type SPR-spring series as well.

The spring diameters are either 11mm/8mm, or 13mm/11mm. The 11mm/8mm springs are similar to the size of the original spring, so if you're upgrading only the spring (which is fine for mild upgrades), then this smaller size is better for you. You can also upgrade the spring guide (7mm type) and a piston with a smaller diameter is also available.
The larger VSR springs and SPR series are better if you upgrade to full PDI internals, because most PDI pistons and spring guides are made with the larger springs in mind.

How to calculate the right percentage for the desired velocity? PDI have a system based on the energy output, so a 300% spring does not mean tripled velocity, but tripled energy. In the case of VSR-10 series, 100% is set to 0.8 joules. Please note that these are approximates, and the final output can be fine-tuned with washers.

PDI have kindly provided us with numbers of the fps ratings of their current spec VSR springs as follows:

  • 130% - 370 fps
  • 140% - 380 fps
  • 200% - 430 fps
  • 250% - 440 fps
  • 280% - 450 fps
  • 330% - 460 fps
  • 360% - 470 fps


    The manufacturing method for PDI cylinders is cold-forging, which is how real sniper rifle barrels are produced. The machinery used in this process costs as much as a new sports car from the higher end, but the achieved super-tight tolerance of a hundredth of a millimeter makes these cylinders the most accurate ones on the market. The slots are laser-cut and the rear shaft is precision-welded in place for ultimate strength.

    PDI makes two main types of cylinders for the VSR-10 series: Precision and B-UP. Regular cylinders have a bore diameter of 22mm, while the B-UP series are a whole millimeter larger at 23mm. Every part inside the cylinder has to be B-UP type, and you need to use special rings inside the receiver as well.

    It is common to mistake the purpose of Bore Up to produce more air for longer barrels. While it certainly helps a little bit with longer barrels as well, the primary reason to increasing the cylinder bore diameter is to improve efficiency; More velocity with the same spring! PDI makes a short-stroke cylinder head in B-UP size as well, so users of shorter barrels can enjoy the benefit as well.

    As the surface area of the piston is increased from 380.133 to 415.476 square mm, it pushes more air for every millimeter of its travel. Because the weight of a B-UP piston is practically the same as normal and the BB is light in comparison, the piston speed is virtually fixed. The volume of the displaced air is increased by 9.3% and it's pushed out in the same time, which means that the velocity of the BB increases.



    When it comes to pistons, PDI have quite a lot of different designs for different purposes. As explained under CYLINDERS, you need to choose between normal size and B-UP first. Also some pistons have a small diameter for 11mm/8mm springs, so do mind that as well. Most pistons are for 13mm/11mm springs. After choosing the right size, it's a matter of structural strength according to the power level: Barikaru are the lightest pistons, and should not be used with ultra-strong springs. These pistons are the ultimate lightweight option when you need the best precision, as they eliminate a lot of vibrations from the piston acceleration and slap. Then come the aluminum pistons with slits cut into them, and finally the enclosed Hard pistons.

    There are two main types of piston heads: Vacuum (VC) and Hard (HD). The Hard piston provides a seal all the time, so it doesn't need to be explained. Both piston heads are ported to provide a tight seal on the way forward without unnecessary friction.

    The Vacuum piston has a hole in the middle of the piston head, with a small rubber ball inside. The need for this arises if you're using a long inner barrel: When the piston has pushed all the air out of the cylinder but the BB is still in the barrel, the dropping pressure could reduce velocity. The PDI vent design allows air to get into the barrel to eliminate negative pressure. Please see the diagram on the left for a cut-away view of the design.



    You would think that there's not much to a spring guide, and just one or two types would be enough, right? Well, the spring guide itself is a simple part, but it has to fit the rest of the parts so choose it carefully! Here are the variables that affect the choice:

  • 7mm or 9mm spring guide for 11/8mm or 13/11 springs respectively
  • Normal or B-UP spring guide to match the cylinder size
  • VC or HD type. (VC is shorter to make room for the vent of the piston head; Will also work with other pistons.)


    Yep, that's what we said when we first heard about this as well. It's a special surface treatment for stainless steel, done in an incredibly low temperature nitride salt bath. Due to material properties, it can not be applied to regular carbon steel. It leaves a nice dull black color to the part, and provides a high surface hardness for reduced friction. It is much more scratch-resistant compared to teflon surfaces, so we finally get to keep and eat the cake!


    When the spring tension becomes high, it can have surprising effects. The original VSR sear system was designed to provide a light and crisp trigger pull, and most PDI parts follow that idea. The 1st and 2nd sear are available - CNC-machined from carbon steel - but for the very highest power levels PDI redesigned the angles to prevent the piston rear from pushing up against the cylinder surface. The V-Trigger comes with a suitable piston end to fit regular and B-UP cylinders. Please see the diagram on the left for the famous picture that tells more than this paragraph.


    While achieving the ultimate performance from your airsoft rifle requires skills from the technician, it certainly does help to have the best possible parts to work with. The above text should give you an idea of how to choose parts for your VSR-10, but if you are the least bit uncertain, it is not a bad idea to ask us to build a custom rifle for you. You can also e-mail us with further questions and suggestions: This article was done based on frequent customer feedback to clarify the use of PDI parts. We listen to your ideas!

    -RedWolf Airsoft