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Tech index -> Shocker SFT -> Adjusting and maintaining -> NDZ adjustable bolt guide

Theory: The concept behind the function of the bolt system in the Shocker is based on the concept that air will be released only when the bolt is in the full forward position. When the bolt fires, it takes a small amount of time to move into this "closed" position, where it will then wait for the dwell time to expire, then recock back to the open position after firing.
The amount of time that the bolt is forward is the amount of time that pressurized air will have to expand behind the ball and accelerate it. Longer time will allow more energy to be used, which will increase velocity (and vice-versa). The function of the NDZ adjustable bolt guide is to alter the position of o-rings and limit this "forward" time by a very small amount, which translates to a larger change in performance (velocity in this case).

The reason why there is a pressure/dwell limit to lowering one's velocity (to indoor requirements) is because pressure and dwell are required to allow the bolt to fully cycle. You can't lower both of them below a certain amount or it will prevent the bolt from cycling and usually create inconsistencies. The purpose of the NDZ adjustable bolt guide is to change the point during the bolt's firing stroke when air is released. What this does is allow less energy to be released to fire the ball while maintaining a proper cycling dwell and pressure combination.

Setup:
The adjustable bolt guide uses a threaded backplate to screw into the Shocker body, a threaded shaft of specific adjustable length, and a threaded lock screw to prevent the shaft from adjusting itself. On the rear of the guide, there are two additional o-rings (13/70 and 14/70), both of which are used as bumpers for the new components. Located between the end of the shaft and the lock screw is a third o-ring (14/70) which also provides a bumper seal between them. All three of these bumper o-rings prevent the guide from locking up when adjusting.

The shaft is adjusted with a 3/16" allen wrench (same wrench used to remove the stock bolt guide) whereas the lock screw is adjusted using a slightly larger 7/32" allen. You will use this 7/32" allen wrench to remove the bolt guide for regular maintenance to the rest of the firing assembly.
Like the stock bolt guide, this one uses a pair of 12/70 o-rings at the front and a single 22/70 o-ring at the rear. The 12/70's are used to seal the bolt, but the 22/70 just acts as a bumper. The NDZ bolt guide will function with any bolt assembly made by Smart Parts, New Designz, or Freeflow. It will infrequently work with the Evolve bolt, however most of the time they aren't compatible (the Evolve bolt is machined slightly larger so the 12/70 o-rings sometimes don't seal).

Adjusting:
I suggest you make all adjustments to the bolt guide with it outside of the gun. This will make it easier to view how much you change the shaft length, and will also help to avoid any problems with lodging the threaded backplate into the body (where you'll have to drill into it in order to remove).

The best way to adjust the guide is to measure the length and use that amount to lengthen it. For the purposes of this guide, I measure length of the shaft from the edge of the bumper on the rear, to the edge of the front o-ring groove. When measuring, you must measure with the bumper installed, or you'll have an inaccurate reading (the bumper is what stops the backplate from being screwed too far into the body).
The default length for the bolt guide is 3-5/8". This is the length of the stock bolt guide.

So...when trying to limit the velocity on the marker, you will want to screw the shaft out more and make it longer than this "default" length of 3-5/8". However, you can't screw it too far, or the marker won't cycle properly due to the bolt air ports being covered up. You can experiment with this on your own.
When making adjustments, make only small differences in length at one time. This may take more than one try to get correct, but it is the best way to go about adjusting. I would suggest at most one-half turn of the allen wrench. Very small changes in length will translate to larger differences in performance.
Additionally, when measuring, be sure you have the correct numbers. It's better to measure more than once and get it right.

When you find your new length, drop in the 14/70 o-ring behind the shaft then screw on the lock screw with your 7/32" allen wrench. Screw it in as tight as possible however be careful not to accidentally change the shaft position when you do. In some cases you may find it necessary to screw the length of the guide a little short to compensate for when you lock it into position and accidentally screw it out a little more in the process. This sometimes happens, but isn't always an issue.

Screw the bolt guide into the Shocker body as normal then test it out. If you are still unable to lower your velocity far enough, remove the bolt guide and screw the shaft in a bit further. If you experience problems removing the lock screw, use a large pair of pliers or channel-lock pliers to grasp the exposed depression, marked in this rendering:

While lengthening the guide will decrease velocity, it's alternately possible to increase it by shortening the length of the guide. However, this will require a lower pressure or lower dwell to achieve the same velocity, while at the same time efficiency will most likely suffer (in this case). I don't suggest making the length shorter than the default length of 3-5/8".

Related Links:
· Setting electronics and pressure

Navigation:
Tech index -> Shocker SFT -> Adjusting and maintaining -> NDZ adjustable bolt guide