Shocker SFT bolt design & theory ZDSPB.com > Tech index > Shocker SFT > Parts of a Shocker -> Bolt design & theory
ZDSPB.com > Tech index > Shocker NXT > Parts of a Shocker -> Bolt design & theory

This page contains expanded technical information on the operation of a Shocker SFT or NXT. This page has a large amount of assorted information which I've attempted to organize to be best of my ability.

Firing Cycle Overview:
Shockers qualify as a "spool valve marker" wherein the bolt acts as its own valve, and the bolt is the marker's primary moving component. When the bolt moves forward, internal air passages eventually slide over an o-ring on the bolt guide, which releases stored air within the fire chamber. This firing air is allowed to expand through the bolt face where it propels the ball.
After firing is complete, the bolt retracts backward, which closes the fire chamber's ports and prevents release of additional air. Once the bolt reaches the full-rearward position, the marker waits until called upon to fire again.

The advantages to spool valve markers generally include decreased recoil, a quieter sounding shot, and a simplistic valve layout which relies entirely on o-rings rather than proprietary face-sealing components such as those found in hammer/valve markers. The disadvantage of spool valve markers is that the firing valve takes more time to open, which tends to decrease air efficiency compared to hammer/valve markers. The slow-opening firing valve, combined with lack of hammer, lead to most spool valve markers sounding quieter than their hammer/valve counterparts. Similar designs can be found in several other markers, including the Dye Matrix and DM, Smart Parts Ion/Epiphany, FEP Quest, DLX Luxe, Empire Vanquish, Eclipse Geo, MacDev Droid, and others. In the future we may come to see additional designs like this, since it is a very simplistic method of firing a marker with many possibilities for modification.

Firing Assembly Synopsis: Tech
Now for some technical information and further explanation of the firing cycle. You may wish to use the first animation listed below for reference. While the solenoid rests idle, the front portion of the bolt sleeve is pressurized, which holds the bolt in the rear/open position. The fire chamber is filled with pressurized air, ready to be released when the bolts fires. To fire the marker, the solenoid energizes and switches its internal spool valve, which is connected to the Shocker bolt sleeve. Switing the solenoid causes the front of the bolt sleeve to vent its pressure while simultaneously the rear of the sleeve becomes filled with air. This action drives the bolt forward; once the bolt reaches the end of its forward stroke, the ring of porting at the front will cross over the tip of the bolt guide and all the air pressure within the fire chamber will be released to the inside of the bolt and out the front, firing the paintball in the chamber. After the dwell time expires, the solenoid switches back which vents the rear of the bolt sleeve and pressurizes the front. This retracts the bolt and also opens up the fire chamber in the HE-style Shocker assemblies.

Non-HE Shocker bolt animation
Above: Stock non-HE bolt animation. Click here for a slower animation. Please note that Shocker NXT markers come with the upgraded HE bolt as a standard part (animated below).

The marker's bolt will be actuated upon the venting/pressurizing that's operated by the solenoid valve. The most important factor is the use of the dwell time, which is the time the solenoid remains energized, which translates to how long the bolt takes to move forward and release pressure. The dwell setting must be set high enough to allow the bolt to cycle forward and dump pressure to fire the ball.

The solenoid's air passages are connected to the bolt sleeve using threaded rods called solenoid inserts. These rods are used to shunt solenoid pressure to different parts of the gun as needed. Pressure from the inserts is exchanged with the bolt components by ports drilled through the bolt chamber wall (they are vertical in the bottom of the body, covered by the set screws on the bottom).

Bolt Moving Speed: Tech
No matter what paintball marker you're describing, it's always important to remember that dwell time isn't simply the "bolt forward time". In reality, the action of the bolt moving to the forward position takes around 80% of the dwell time, after which the remaining few milliseconds are used to release pressurized air to fire the ball.

The Shocker bolt usually stays in the forward position for 1-2 milliseconds, while the rest of the dwell time is used to move it forward (8-10 ms or higher). Other types of spool valve markers tend to require longer to release their pressure since the dump chamber is located further away from the chamber. The design of the Shocker is such that the proximity between the fire chamber and the breech reduces the amount of time it takes pressure to release, as well as limiting the amount of energy that is wasted in the release itself. This makes the Shocker one of the foremost spool valve designs due to the placement of the dump chamber alone.
This is contrasted to some other spool valve markers, such as the Ion or Matrix, where the dump chamber is located at the rear of the marker. These designs require air be shunted through their bolt sleeves to reach the bolt face. As a result, they tend to require an additional 1-2 milliseconds to fully dump their pressure. I measured these characteristics through extensive real-time testing and evaluation.

Solenoid Air Supply: Tech
The solenoid valve is supplied with low pressure air via the left solenoid insert rod, on the left side of the marker body. This section of the marker is fed by the low pressure air supply in the vertical adapter by a single 0.046" diameter air port at the front of the body (smaller than 1/20"). This port is drilled in such a small size specifically to prevent the solenoid's air supply from being starved by the fire chamber when the marker fires the ball. This means that a larger port would allow the fire chamber to seal pressure from the solenoid, causing extreme cycling problems (inconsistency, velocity dropoff, in extreme cases the solenoid wouldn't be able to retract the bolt). This is a specific design of the marker and shouldn't be tampered.

Since the air supply is relatively small, the rear of the Shocker bolt sleeve is used to store additional air volume to help resupply the solenoid. The bolt sleeve acts as a solenoid volumizer to ensure adequate pressure is always available for firing the fastest speeds possible. The pressure reservoir is isolated from the fire chamber since it is fed through the left solenoid insert.

Bolt Moving Force: Tech
The design of any spool valve marker bolt will utilize air pressure to push the bolt forward. The air pressure responsible for moving the bolt also determines the specific force at which the bolt will be pushed. The determining factor is the size of the surface area on the bolt being acted upon. Bolt force is calculated by multiplying the surface area by the air pressure (surface area * pressure).

Most Shocker bolts have a bolt sail surface area of 0.083 square inches. For example, if running 180-psi, bolt moving force is calculated by (0.083 x 180 = 14.9 pounds).

Evolve v1 and v2 Shocker bolts have a bolt sail surface area of 0.128 square inches. For example, if running 170-psi, bolt moving force is calculated by (0.083 x 170 = 21.7 pounds).

Most spool valve markers operate between 15-20 pounds, depending on the design of their internals. Markers that require a low pressure regulator for the solenoid (LPR) are specifically designed with higher surface area to equal the same bolt force. Generally, bolt forces less than 12 pounds do not move fast enough to cycle reliable enough for firing paintballs. Therefore, both markers with and without LPRs will operate their bolt with virtually identical moving forces.

For the same reason, Shocker LPR adapters only allow a very small decrease in solenoid LPR pressure because the bolt will quickly fall below the threshold for minimum moving speed. LPRs can be used to squeeze out a small performance gain, but often beyond the perception of most players.

Aftermarket Bolt Assembly Designs:
Smart Parts High-Efficiency (HE) bolt kit: (also known as Turbocharger bolt)
The HE bolt from Smart Parts uses a special "air spring" design whereby the bolt is used to seal off fire chamber input when in the firing position. The spring action comes because the fire chamber input assists in pushing the bolt open once firing has completed. The HE bolt was used as an upgrade for any Shocker, but was almost always a stock item with private label Shockers, then later became a stock part for Shocker NXTs.
HE bolt
Above: HE-style bolt animation. Click here for a slower animation. This animation also applies to any HE-style component such as NDZ bolt, Nox bolt, Eigenbolt, etc.

NDZ v3 bolt components: The NDZ Stinger v3 bolt assembly uses identical design as the HE kit from Smart Parts. The only functional difference is that the NDZ fire chamber is designed to hold more volume, thus allowing the NDZ bolt to use a single row of ports instead of the elongated ones used with HE bolts. The NDZ bolt functions at a lower pressure but this isn't necessarily a performance increase, rather a different way to accomplish the same task.
Evovle ULP components: Evolve's ULP design was meant to be compatible with more common HE-style bolt parts. The bolt and fire chamber can be interchanged with HE, NDZ, or other parts.

Evolve v1/v2 bolt system: Evolve's upgraded Shocker bolt assembly was the first aftermarket system to be released for Shockers. This bolt also uses a design which seals off input during firing, however the Evolve version works a little differently than the HE bolt. Evolve bolts use a balanced air input which is sealed off using additional o-rings in the rear of the fire chamber. The bolt has an array of external grooves which facilitate fire chamber filling when idle, and seal off fire chamber when the bolt moves forward. This design was patented by Evolve.
Evolve bolt
Above: Evolve bolt animation. Click here for a slower animation.

Shocker air volume:
Dump chamber air volume information is listed below. To calculate the air volume used in your marker, add the volume numbers for your fire chamber plus bolt guide.

Fire chamber type: Air volume:
(cubic inches)
Bolt guide type: Air volume:
(cubic inches)
Stock non-HE fire chamber 0.846 Non-HE bolt guide 0.0
HE fire chamber 0.760 All HE-style bolt guides 0.150
NDZ v3 with side o-rings 0.818 NDZ adjustable bolt guide 0.160
NDZ ULP fire chamber 1.036 Pooty LP bolt guide ??
Evolve ULP fire chamber ?? ULP-modded bolt guide (1/4" hole) 0.233
Nummech LP bolt guides (3/8" hole) 0.376

According to the chart, increases in available air volume can be obtained by using a ULP fire chamber or using a ULP bolt guide. For instance, the use of an HE fire chamber with a ULP bolt guide will allow similar air volume if using a ULP fire chamber with standard bolt guide.

Generally, using components with increased air volume will allow for lower operating pressure. However, remember that Shocker bolts require a minimum bolt moving force, which is determined by operating pressure. Therefore, most Shockers will have trouble cycling if the operating pressure is reduced below 160-psi. It's possible to use an operating pressure below that amount but it usually requires extensive tuning and experimentation with different o-rings and lubricants.

Related Links:
Stock bolt manual scan
Solenoid inserts
Solenoid