Springs:
There are currently three series of springs that can be used within the VSR series. The EZY series features a 7mm diameter spring in a variety of power levels. These springs can also be used with the stock spring guides and pistons (you must use the lower power springs with stock parts).
The SPR series are a 9mm diameter spring originally used for the APS2 rifles, they will also work superbly in the VSR. These springs feature a softer and easier pull for the power output they produce. The SPR series springs are a current favorite of mine for bolt gun upgrading.
The SS series are meant as an “export only” spring in Japan. Producing great amounts of power. (These springs produce more power than the ASGK allows for gaming in Japan). There is even a warning from the manufacturer about excessive damage when using this spring series. -At least they’re up front about it.

Spring Guides:
Two types of spring guides are currently offered. There is a 7mm diameter and a 9mm spring guide. Both feature a one-piece construction and a plastic washer cushion for the spring. ‘Spring Tension Ring’ kits are available and can be used together to correct for power loss during break in of the spring.

Cylinders:
New cylinder kits are now available for many types of barrel lengths and power level considerations.
There is the basic ‘Straw’ cylinder, a stock replacement for the OEM unit. Also, a new Laser cylinder, featuring laser welds for almost unbreakable performance.
A new Bore-Up cylinder kit is available, as well as a new ‘High Speed’ ported unit for the shorter 303mm Gspec barrel users. As well as a new ‘Premier’ kit for ultra high velocity power applications.
Along with the cylinders, there is a Tapered Cylinder Head unit available in both standard size and for Bore-Up applications. The Tapered Cylinder Head allows better airflow during firing allowing an increase in velocity and consistent shot power.

Pistons:
A wide selection of pistons is available for any power and performance level that a player might be looking for.
The S-Piston is an entry level reinforced piston used with 7mm springs.
The Hard Piston will accept 9mm springs, and seems to be the most useful in the widest array of power and performance selections.
For very long barrel assemblies, PDI offers the Vacuum Piston. This piston uses a small bearing unit to correct for air volume in the cylinder versus the air volume in the barrel. An interesting way to combat the ‘vacuum effect’ of very long barrel systems and to preserve velocity.
Lightweight plastic piston units (Barikaru) offer higher velocities for lower power spring set-ups. All pistons mentioned also come in a Bore-Up size as well.

Trigger Kits/Parts:
These parts allow the piston to be held back when using stronger springs. Stock trigger parts are fine for lower power applications (below 350fps).
There are 2 ways to upgrade a VSR trigger group. First, using the OEM trigger housing, you can replace the individual trigger sears with replacement parts made from steel. (versus the OEM parts out of aluminum/pot metal)
The main parts needed for an upgrade are the 1st sear (trigger), 2nd sear (piston). For added durability, the set pin and spring kits are available too.
The second way to upgrade the trigger is to replace it all together!
The Trigger kits are basically a roller bearing type trigger system. While offering a smother trigger pull, they do sacrifice ‘trigger feel’. An important thing to note is that trigger kits use a different piston sear and require the piston to have a corresponding locking end cap. The new kits include either the piston, or the piston end cap for correct use. Regular pistons cannot be used together with the trigger kits.

Tight-Bore Barrels:
PDI offers their ‘tight-bore’ barrels in a 6.05mm inner diameter. They are constructed out of steel, and come in a variety of lengths. The 6.05 barrels seem to offer an increase in both velocity and maximum distance when compared to the Laylax (6.03mm) and KM (6.04mm) barrels.
For supreme accuracy, PDI is now offering a 6.01mm inner diameter barrel in select lengths. Players using these barrels are warned, they must use very high quality BB’s, such as Maruzen .29g Super Grand Masters, and Maruzen .30g ‘Accuracy’ BB’s. Cheap BB’s will get jammed!

Outer Barrel Kits:
PDI offers a stylish alternative to the plain old ‘bull barrel’.
Fluted Barrel sets are now available in both the Pro-Sniper lengths, and a longer style as well. Built strong and durable, they have a nice heft to it. If weight is a concern, PDI has a lightweight bull barrel in different lengths as well. Other than the outer barrels, different receiver types are available as well.

With the availability of such a wide range of parts, there are nearly a limitless variety of styles and combinations for any airsoft sniper or target shooter too choose from and personalize their own way. Players, who want a more in depth look at the parts available, with descriptions and more information, can check out Impact Games’ web page www.impactgamesairsoft.com
Or check out the source: www.pdijapan.co.jp
And their English site: www.x-fire.org