Back to the Basics Series:
Adjusting the velocity in a Nelson based pump paintball gun.

With a little practical application, you’ll have your gun set in no time and understand how it works. A "Nelson" based paintgun, is a single tube design where all the internal parts are inline with each other. Most common are the Trracer/Maverick, and Phantom pump guns. If your gun has a stacked double tube design its most likely Sheridan based (PGP, P68, ect.), and isn’t covered here.

Assuming you have a nelson based marker, you have to figure how the gun was designed for velocity adjustment. There are several different ways, and they can be combined in some cases, the most common these days is the adjustable bolt. Not all guns have them, so you’ll need to take a look if your not sure. If there are slots in the sides of the gun, you might be able to tell from there(the bolt is the part that the pump arms screw into.) Look at the back side of the bolt, inside of it, there should be a hollow , threaded tube. Screwing this tube in or out increases or reduces spring pressure, which in turn changes the gun velocity. If you cant tell from just looking, you’ll need to disassemble the gun and pull out the bolt to take a look at it. Its a good idea to find the proper sized Allan wrench for it while its out, the longer the better. Remember how you took it apart, so you can get it back together again, and always make sure you’ve removed the air source, co2 tank or 12 gram before you start, or you could end up in a world of hurt. The other methods of adjusting velocity are changing the springs, adding spacers, clipping springs, or using a regulator.

If you have an adjustable bolt, and you’ve got your long Allan wrench, your ready to adjust. Put your goggles on, and shoot your gun over a chronograph( available at all paintball fields for use, or you can buy one for about $50.00 us. ) If your shooting above the field speed limit (260-300 fps) , use your Allan wrench to turn the bolt adjustment counter clock wise by inserting the wrench into the barrel side of the gun , into the bolt. Just turn it a little at a time, recheck the gun and repeat until you’ve got it set right. If your shooting to slow, turn it clockwise until it comes up to speed. You may need to remove the barrel for this (make sure there’s no paintballs in there or you’ll have a mess.)

Never fear, you still have options. If you were paying attention, you know that the springs are the real parts that regulate velocity. Buy changing those springs out for "harder" or "softer" ones, you can still get your velocity to where it should be. Nelson based spring kits are available in most paintball stores. They usually come in kits of six or eight springs, and are color coded. Buy a set, there should be specific instructions in the package, but generally red is the hardest spring, and yellow the softest. If your shooting to low, you’ll want a harder spring between the bolt and the hammer. To high? Put a softer spring in .

Those are the valve springs, they live in the Air System Adapter or ASA, (where the tank screws in) on most nelson based guns. When you remove the asa, there should be a nut on the inside end which holds in the valve tube. Carefully unscrew this nut and you’ll find the small spring under it. Here’s the tricky part.. the settings are opposite. That little spring governs the amount of co2 that enters the gun. If your shooting to high, you need a harder spring back there (the valve opens less this way.) if your shooting too low, you want a softer spring in the back so it allows more co2 to enter the gun.

If all else fails, you can add spacers behind your big spring to bring the velocity up. Washers of the proper size will increase the spring tension and your velocity.

If, no matter what you do, your still shooting to fast, you can cut small sections of the main spring off, to decrease spring tension. Be careful here, if you cut to much, you’ll need a whole new spring. Just cut one "ring" at a time, test it out, and take it from there.

Regulators: you can also use a regulator to adjust you velocity by increasing or decreasing gas flow at the regulator, but you still need to get your gun in the ball park by using the methods above.