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AirGun Designs

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Building an ULE Automag
by Bill Mills - Part 1 - Part 2

Our construction and testing of an ULE Automag continues with the installation of the X-Valve into the assembled receiver.

Initial assembly of the X-Valve consisted simple of sliding the entire bolt and valve assembly into the body, and locking it into place with the rear grip frame screw.  While this screw has a hole for a hex wrench, it is meant to only be tightened finger tight – the hole is to use a wrench if it is difficult to loosen by hand.  

The final item to complete this new ULE Mag as a paintgun is the ULE trigger pull upgrade, a new product released in the summer of 2003.  While it is often referred to as the ULE trigger, it is actually an upgrade to the on/off valve assembly which reduces both the length and the weight of the trigger pull.  To reduce trigger pull length, AGD looked at how their on/off valve worked.  A pin, that is pushed by the rear of the sear slides up into the center of an o-ring sealing off that opening between the regulator and air chamber.  On previous Automag valve designs the pin pushed up and through the o-ring.  AGDs designers realizes that this was unnecessary, instead of pushing up and through, the on/off pin only needed to be pushed far enough to make contact with the oring – just to the point that its edge pressed up to the o-ring’s interior.  This idea alone reduced the distance the pin needed to theoretically move, and thus the length of the trigger pull.  

Trigger pull weight was another matter.  The Automag has no trigger return spring.  Gas pressure pushing against the on/off valve pin resets both the valve and the trigger.  The force involved comes from both the pressure of the gas, and the diameter of the on/off pin.  Basic hydraulic ram principles dictate that the same pressure (the pressure must be the same to maintain the same velocity in the Automag) a larger diameter piston will provide more force than a smaller diameter piston because there is more surface area for the gas or fluid to press against.  

The new ULE on/off assembly features an on/off pin that is made of two pieces.  The bottom piece is a larger diameter, so that the back of the sear can press up against it.  The top piece has a large enough head to seal the on/off o-ring, but is extremely slender in the center.  Slender is perhaps an understatement.  The center section of the ULE on/off pin is 0.035 inches in diameter, or approximately the size of a bundle of 10 human hairs.  

When the on/off valve is open, that diameter is what determines the resistance of the trigger pull.  In a properly set up Automag ULE trigger system, the trigger pull will not only be short, but it will require less than one pound of force – something previously only available in electronic paintguns.  When the on/off valve closes at the end of the trigger pull, the larger diameter of the on/off pin top comes into play and the trigger pushes back to its reset position with significantly more force.  This is a reactive trigger effect that makes certain the trigger fully resets and helps the user pull the trigger faster.

Installing the ULE on/off has a few steps.  First it must be assembled.  Some users opt to use a thread locker to glue the two on/off pin pieces together.  This is a good idea as it will make it difficult to lose, however, it also makes changing the pins lower o-ring impossible.  The exact point at which the on/off valve closes, relative to when the bolt is released is critical to the operation of the Automag, so much so that putting a coat of paint on the body rail can put this fine balance out of adjustment far enough to keep the ‘gun from working properly.  In the past some airsmiths have tuned up Automags by grinding down on/off pins to get a custom fit.  With the ULE on/off the fit is even more critical, so making adjustments would be necessary.  

Unfortunately it is not practical to make a steel pin that small to be adjustable in length in the very fine increments needed.  There is an old saying, “if Mohammed can’t come to the mountain, the mountain will come to Mohammed.”  Rather than adjusting the pin length, AGD’s designers added adjustability to the position of the o-ring the pin seals against, in order to achieve the same effect.  The top half of the valve rests on the bottom half, held there by air pressure.  The two parts have screw threads so they can be taken out as a single unit without bending the pin, but when putting them together the threads pass each other and the parts float freely.  A set of shims are included in the ULE on/off kit to go between the two valve halves.  More shims mean that the top half of the valve will be higher up inside the X Valve body, and has the same effect as shortening the on/off pin.  Conversely removing shims lowers the valve body and has the same effect as putting in a longer on/off pin.

Once the ULE on/off valve is assembled, it slips into the X Valve, replacing the stock on/off valve.  It should be noted, that the ULE trigger upgrade will only work on specific model Automag valves, some valves which are designed to hold a single o-ring on top of the on/off valve instead of two nested o-rings, will not accept the ULE on/off.

With the ULE trigger mod in place, the new ULE Mag was assembled and ready for an air system and adjustment.  For review, and Airgun Designs Flatline 4500 psi compressed air system was used, mounted on a Custom Products drop forward and hosed to the X Valve with macroline.  During all the firing needed for adjustment, a Centerflag Ninja muffler was used in place of a barrel.

While Level 10 and the ULE trigger Kit represent marked performance increases for the Automag, they also represent an increase in set up and maintenance time.  To ease some set-up woes, AGD includes a credit card sized CD-ROM manual with the Level-10 kit, but a more visual set-up video is available on the web forum site, produced by “Miscue,” one of the forum moderators.  To allow for manufacturing variances in o-rings the Level-10 kit ships with several brass carriers, each with differing inner diameters.  These carriers are then fitted with the power tube o-ring to find a fit that will seal against the piston in the bolt, sealing it with the least amount of friction possible.  Several selections were used tried, as well as all three mainsprings, until a balance was found that would fire reliably, yet allow the bolt to bounce back off of a finger in the feed neck.  Similarly several trials were made with varying shim combinations in the ULE on/off assembly.

In all, adjustment took approximately one hour, with each adjustment affecting another.  When the proper balance was found, the ULE Mag was ready to go, and any further adjustments should be rather quick, as they will just need to tweak a single variable at a time.  For review, the ULE Mag was fitted with an SM-1 barrel kit from Sanchez Machine, and a Revolution loader with X Board and JMJ Impeller.

On field, the ULE Mag delivered as promised.  It was extremely lightweight, did not chop any paint.  Most notably it had a trigger pull comparable to those of electronic paintguns.  The trigger pull was extremely light, and had an active length of less than 1mm in length measured at mid-trigger.  The only thing that seemed to be limiting shooting as fast as most electros was an excess of trigger slop.  That is, while it took a pull of less than 1mm to fire, the trigger could still be pulled back all the way up against the trigger frame.  The addition of trigger travel limit screw by an airsmith would stop the trigger just past the firing point, making higher rates of fire very easily obtainable.  Also very significant was the overall size and weight.  The ULE Mag was markedly lighter than an E-Mag, due to the lack of battery pack.  It was also lighter, and smaller than many other paintguns on the market while delivering a high end trigger pull and anti-chop capability.  At the present a ULE Mag can be built from components, but a similar configuration is likely to be available ready to roll at some point in the future, from AirGun Designs.

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