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Tips
Welcome to "Tips from the Workbench". This month I will cover
maintaining your Nelson based pump-gun. What is a Nelson based pump-gun?
Nelson based guns are easy to use and maintain, and give you very good
performance. The design is simple...there are only two springs and a few
of o-rings to deal with. The main components are the cup seal, bolt, power
tube hammer/sear, valve, and trigger mechanism.
Back in the early to mid 1980's the Nelspot 007 pump-gun was designed and
sold to the Paintball industry. At the time it was considered one of the
better guns (There were only four or five available). To this day the Nelson
design is still the most popular of all pumps. This is how the Nelson based
pump guns work:
C02 is supplied to the gun through the ASA (air source adapter) and paintballs
rest in the feed tube. When the gun is cocked, a ball drops into the breach
and the main spring is compressed simultaneously. When the pump handle is
pushed forward the ball slides into the barrel. The trigger is pulled releasing
the sear. The spring forces the hammer back, slamming into the rear of the
power tube releasing the C02 that propels the paintball.
Maintaining your Nelson based pump-gun
Velocity adjustments and problems: Depending on which Nelson based
gun you have, you may or may not have a velocity adjuster. If you do it is
located in the bolt (called an adjustable bolt). Screwing the bolt in or
out puts more or less pressure on the hammer spring which allows the hammer
to hit the valve softer or harder. The harder the valve is hit, the more
C02 will be released increasing the gun's velocity. If your gun does not
have a velocity adjuster you can change your hammer and/or valve spring (the
valve spring is located in the rear of the gun) to increase or decrease the
velocity. Please make sure you chronograph your paintgun whenever velocity
changes are made.
If you are experiencing erratic velocity make sure your gun is clean
and properly lubricated. Broken paint in the barrel will mess with your velocity
almost as much as it does your accuracy. Also, your internal parts need to
move smoothly so they must be lightly lubed. Place a few drops of oil in
the hammer/bolt area and in the constant air adapter. Dry fire the gun (without
the barrel on) to disburse the oil in the c/a adapter.
Air source types and problems: We've been asked many times if it is
alright to use a siphon tank with a pump gun. Siphon tanks work well with
most Nelson based pumps, but they work the gun harder. Many players use siphon
tanks in the winter when the weather is cold. A siphon tank will improve
your cold weather performance greatly, but won't do a thing to help you out
when its warm. Like any paintgun, keeping consistent C02 pressure to your
Nelson based gun's valve is important to good performance.
Air leaks: If your pump gun makes a popping sound when you pull the
pump handle back or air is leaking down the barrel, chances are you have
a bad cup seal. Replace the cup seal and your problem should go away. If
your gun is leaking from around the constant air adapter it is most likely
caused by a bad tank o-ring. Again change the o-ring to fix the problem.
Miscellaneous tips: With most (or all) pump guns, the pump handle
is connected to the bolt. Make sure both pump handle screws, if there are
two, are in place. With only one screw the handle will bind when you try
to pump it. To help prevent losing your pump handle screws, place some Teflon
tape on the threads. This will "snug" the screws in place better.
The grip handle on your pump gun has a tendency to come loose occasionally.
Simply look inside your grip handle (from the bottom) and see what type of
screw is holding the grip handle to the receiver. It will either be a large
allen screw or a flat-head screw. Tighten the screw and you'll be alright.
That's my time for this month. Please play safe, wear only Paintball approved
goggles, and play at organized fields. Thanks for reading.
(About the author...Rick Muncy is an Airgun Designs Certified Technician
and works as an airsmith at Pev's Paintball Pro-Shop in Woodbridge, Virginia.)
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