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Pro-Team Products’

RetroValve Micromag


© Ravi Chopra, 1999

I’ve wanted to write an article about the Automag RT since it first became available. This stems from my admiration for the original Automag’s design. When the Automag finally hit level-7 (the first truly usable and reliable Automag), the other semi-autos on the market were predominantly kludgy blowbacks. The Autococker was around, but it was still in the midst of it’s worst growing pains and was best known for blown hoses and being "the semi-auto version of the Sniper pump." The Automag on the other hand, was a revelation. It was smaller, faster, and flat-out cooler than every other ’gun on the market. From an engineering perspective, it was sheer brilliance. To this day, I am still taken with the beauty of the Automag’s design. Even today’s most expensive, cutting-edge electropneumatic paintguns borrow heavily from semi-autos and pump-guns of years past. The Automag was completely unlike anything that came before it. What’s more, it’s design is incredibly simple. Troubleshooting rarely entailed more than five minutes spent going through a flow-chart in the manual. 90% of the problems could be corrected by simply replacing an O-ring.

But time can bear harsh witness to stagnant technology. Though the Automag did receive a steady flow of small improvements through the years, much greater improvements to competing paintguns started chewing into the Automag’s tournament-dominating market. Less was spoken of it’s exceptional rate-of-fire, while more and more attention turned to the velocity drop-off problems that many people experienced during rapid-fire. Airgun Designs needed something new that retained the Automag’s strengths while taking it up a level on the performance ladder. Their answer was the Automag RT, an Automag with a "Reactive Trigger" that kicks back out with greater force than it takes to pull. What’s more, the RT has a recharge rate so fast that it leaves the original Automag in it’s dust.

I actually bought an RT when they first came out. I was very impressed with the new design. The RT isn’t a revolutionary new design like the original Automag was, but it is a brilliant evolution that, to me, truly emphasizes the brilliance of AGD’s engineers. I wanted to write an article about it even then, but those familiar with all my articles know it was never written. I ran into a problem that I just couldn’t find a way around. The thing broke paint. I don’t mean it broke one in every thousand, or even one in every hopper. I mean that if you didn’t know what was going on, watching me shoot that RT you could easily have been convinced that someone had filled my hopper with confetti. I tried the original high-rise powerfeed and broke too much paint with that. So I switched to a body with the standard powerfeed and still broke too much paint. I tried different barrels, different paints, all with the same discouraging results. Making matters all the more frustrating, I watched other teams tearing people up with their RTs and not breaking a single ball. Convinced that I was doing something horribly wrong but unwilling to shred more paint trying to figure it out, I gave up, crawled meekly back to my sweet Bad Boyz Toyz Autococker (which never broke paint), begged for forgiveness and forgot all about the whole thing.

Well, it was all brought back to me just recently. Pro-Team Products had just come out with an RT version of the Micromag– really nothing more than a Micromag body with the RetroValve installed in place of the standard Automag parts. For those who aren’t familiar with it yet, the RetroValve is essentially the RT’s internals with the gas inlet on the side so they can be installed in any original Automag body. I’d reviewed the original Micromag a few years back and had been impressed with a lot of it’s innovations and features. In the years since, PTP has updated and improved quite a few things on the Micromag. They wanted me to evaluate the updated version. With some trepidation and nothing but the worst of expectations, I accepted. Shortly thereafter, I received a RetroValve Micromag Plus upgraded with a double-finger trigger, Wild Tiger anodizing, and one of the new 13" Armson Stealth barrels.

Before I go on, I’ll let you in on a bit of the conclusion. I don’t know if the RT’s design has been improved or if I’ve just changed somehow, but the RetroValve Micromag worked quite well for me. It was a far cry and dramatic improvement over the paint-shredding exercise in frustration that I’d encountered some years back.

How the RT Works

I’m not going to go into all the details of how the Automag works, how the on/off closes the flow of gas just before the bolt is released and all that. That has been described countless times in many other places. The RT is very similar. What I am going to focus on here is the differences between the RT and the Automag, and how those differences contribute to the "reactive trigger" and the much faster fill rate.

Before I can explain how the RT works, I have to explain a few things about the physics of gas flow and how regulators work. No equations, I promise.

First, flow rate is determined by several factors. In a paintgun, the biggest issues are pressure gradient and channel size. By pressure gradient, I mean the difference in pressure between where the gas is coming from, and where it is going to. If you were to open a full 3000 psi nitrogen tank to the open air, the pressure gradient across the valve would be 3000 psi. Flow rate is directly and linearly related to the pressure gradient. Essentially, this means that the higher the pressure difference is, the faster gas will flow. If you double the pressure difference, you double the flow rate.

Channel size is just what it sounds like; it is the size of the gas path, the diameter of the tube the air is travelling through. Obviously, the bigger the channel, the faster the gas can flow. This is not a linear relationship, though. In fact, this is a fourth power relationship. What this means is that if you double the diameter of the tube, you increase the flow rate by sixteen times! It is because of this that people always drill out their Automags and chop up their on/offs in hopes of achieving better flow and faster recharge rates. It is also based on this that people regularly drill out air passages in their paintguns to achieve lower operating pressure: a certain amount of flow can be accommodated at a much lower pressure gradient if the channel is larger.

Now, how regulators work. All pressure regulators work essentially the same way – by balancing the input pressure against a spring tension, separated by a piston. A valve is coupled to the piston such that when the spring is compressed and the piston can move back, the valve is closed, shutting off the flow of air. When a spring is compressed, it applies a certain amount of force. Pressure is measured in psi – pounds per square inch. In other words, forcer per area over which that pressure is applied. The piston is the area over which that pressure is applied. Multiply the pressure by the area of the piston and you get a force. So you can see, as air flows into the regulator, it presses against the piston with a certain amount of force. When the pressure climbs to a level where it is pushing harder than the spring, the piston will be pushed back, compressing the spring, closing the valve, and stopping the flow into the valve at that specific pressure. You increase the pressure the valve allows by either increasing the tension on the spring or increasing the distance the spring has to compress before the valve closes.

In the Automag, the incoming full pressure air is fed directly to the regulator piston in the AIR valve and shut off at whatever your set point is, say 450 psi. This 450 psi air is channeled forward to the on/off valve, through it and into the air reservoir behind the bolt. Say, for instance that you set your input pressure to 700 psi, hold the trigger in, and gas the ’gun up. This means that your pressure gradient into the empty AIR valve is 700 psi. The valve allows 450 psi in, and stops the flow there. Now there is 450 psi up to the on/off valve, pushing down on the on/off pin. The other end of the pin is open to the air, so the force pushing back on your finger is that 450 psi multiplied by the cross-sectional area of the on/off pin. When you let go of the trigger, the on/off opens. Since the air reservoir is empty, the gradient across the on/off is 450 psi. Air flows through the on/off and into the air reservoir. Since air is drained out of the channel between the AIR valve and on/off, the pressure drops, so the AIR valve opens to allow more air in, filling the whole system up to the reservoir up to 450 psi.

The RT is similar, but has some significant differences. In the RT, the inlet air does not go straight to the regulator piston as it does in the Automag. In fact the inlet-pressure air is routed up and forward to the on/off valve (the on/off has a special improvement, but I’ll set that aside until later). So at this point, you have full input pressure (700 psi) pressing down on the closed on/off (See Figure 1). When you release the trigger, the on/off opens and allows air in. Air that passes through the on/off goes forward to the air reservoir as in the Automag, but it also is routed backwards, through a tube, and back to the regulator piston. When the pressure in the chambers past the on/off reach the operating pressure (whatever it’s set to, say 450 psi), the regulator piston is pushed back just like in the Automag AIR valve. When it does, the tube which conducted the air back to the piston can move back and seals off the air entering the ’gun (See Figure 2). The end effect is the same; the air reservoir is filled to the regulated pressure. The difference is that it fills much faster since you have that 700 psi gradient across the on/off valve rather than the 450 psi the on/off sees in the Automag.

There is also the question of the "Reactive Trigger." This is accomplished in a couple ways. The first way has already essentially been described. The RT’s valve arrangement is such that when the trigger is released, the system is filled only to 450 psi, so 450 psi is what is pushing down on the on/off, and is the force you are pulling back against when you pull the trigger. When you fire the ’gun, though, full input pressure (700 psi) is fed to the on/off so after the ’gun is fired you have that 700 psi pushing the trigger back forward. Thus, the trigger returns with over 50% more pressure than when you are pulling it. It is because of this effect that you can increase the return force by simply turning up your input pressure.

This is strong return effect is amplified by the new design of the on/off valve. In the original Automag’s valve the valve piston is a simple rod of consistent diameter. In the RT on/off, the valve piston has two diameters: wide at the top where it seals when the trigger is pulled, thinner at the bottom where it seals the on/off from the outside air and where it comes in contact with the back of the sear. Remember that pressure is measured in pounds per square inch – force per area. The area of the top of the on/off is greater than the cross sectional area of the thinner lower stem. Thus, when the trigger is forward and the on/off is open, the pressure inside the ’gun is felt across that smaller area. But when you pull the trigger, you’re suddenly sealing it with the larger diameter stem top. This has a larger cross sectional area, so the force you feel pushing the trigger back is suddenly increased by the amount that the area increased. Since the on/off stem top is about double the diameter of its lower end, the return force is increased almost 4 times (another 200%).

Thus, combining the two components, the on/off return force is about 6 times what it takes to close the on/off from the open position (I’m not going into the math, so if you don’t understand it, you’ll just have to trust me here). Does that mean that the trigger returns with 6 times the force that it takes to pull? Anyone who has shot an RT will tell you that the answer is definitely "no". Why not? The reason is very simple. The trigger pull consists not just of closing the on/off, but also dropping the sear off the front of the bolt. Pulling the sear off the bolt is actually the larger part of the force required to pull the trigger. When the trigger is returning, this is obviously not part of the equation; only the on/off pushes back on the trigger. So, to get a return force that is actually greater than what it takes to pull the trigger, you need this huge amplification of return force in the on/off to compensate for the force you have to apply to release the bolt.

That’s pretty much the whole story. With these small but significant changes to the AIR valve and on/off, Airgun Designs has changed the Automag from a ’gun with a reputation for drop-off during rapid fire into a ’gun that can reportedly cycle well over 20 times per second without losing so much as a foot of velocity. That is, by the way, faster than any of the electropneumatics are capable of cycling.

I’ll say it again; it’s a brilliant design. The engineers at AGD are original and innovative in the truest sense of those words.

The Micromag

Enter Pro-Team Products. Pro-Team has long been the purveyor of the popular Micromag paintgun – a total-body upgrade for the Automag. Now with the RetroValve upgrade for the Automag available, the Micromag can be kicked up with RT power.

It is important to note first that this is not an Automag RT upgrade. The Micromag RT is actually the same Micromag body that they’ve been selling for years. You can not install the RT’s valve in the Micromag. Instead, Pro-Team installs AGD’s RetroValve. The RetroValve is essentially the exact same thing as the RT’s valve, but redimensioned to fit the original Automag’s body, and with the air inlet in the side rather than through the banjo bolt. This way, you can turn any original Automag (or compatible ’gun) into an RT. Very clever and very cool.

As I said above, the Micromag is a total body replacement for the ’mag. It replaces the entire body, rail, barrel, and grip frame. The only parts from Airgun Designs come in the RetroValve: the RT Air valve, bolt, bolt return spring, and sear.

Micromags come in a variety of configurations. All include the body, .45 frame, and powerfeed. Packages are available with different combinations of vertical ASAs, bottom-line adapters, forgrips, barrels, 2-finger trigger frames, and expansion chambers. The Micro RT does not come with an expansion chamber as an option since it is a nitrogen/HPA-only paintgun. That’s right – no CO2 for the RT valve.

The version that was sent to me was a 2-finger trigger RetroValve Micromag Plus. It included a 2-finger trigger frame, gas-through forgrip, bottom-line ASA, and one of the new Armson Stealth barrels in 13" length. Steel-braid hoses with chromed ends run from the bottom-line to the gas-through forgrip, and then from the forgrip to the RetroValve. To me this seems like an awful lot of extra hosing given that you can run your nitrogen straight to the RetroValve. For my tests, I stripped all these extra hoses off and ran my Max-Flow nitrogen system bottom-line. Decked out in Wild Tiger splash anodizing, this ’gun goes out the door for $789.95.

The original concept for the Micromag was a super-light, super-short Automag, specialized for speedball. In fact, the first Micromags were tiny, fixed-barrel paintguns. Over the years, the Micromag body has become quite a lot less specialized and much improved.

The body is manufactured entirely from aluminum and is much shorter and lighter than Airgun Design’s stainless steel tube. It is nicely milled for a custom look. The rail is incorporated as and integral part of the body rather than being a separate part, eliminating the potential for problems with bent rails and other misalignments. The RT sear slips up into a slot in the bottom of the body and is fixed in place with a screw (much nicer than the pin in older Micromags which always wanted to fall out during assembly).

The Micromag body differs from the Automag and RT bodies in more than just cosmetics. There are many significant functional differences as well. First and most notably, Micromags have Autococker-compatible barrel threads. This comes as welcome news to anyone who already has an extensive collection of Autococker barrels. Additionally, some feel that this makes for improved accuracy since the Automag’s slip-and-twist fit barrels are free to wiggle a tiny amount even when locked firmly in place.

With the Automag slip-and-twist barrel goes the oft-broken, much bitched-about wire-nubbin detent. Originally, Pro-Team just screwed their plastic Autococker detent to the side of the Micromag. This sometimes caused problems because if you over-tightened the mounting screws, the detent would bind and you’d break paint. They’ve now eliminated this problem by incorporating the detent base into the ’gun body. The spring-loaded plastic swing arm is unchanged. This is a very good detent that never requires adjusting, won’t break, and won’t jam up. The slot in the side of the ’gun even acts as an extra blowback relief vent.

The Micromag comes with a standard powerfeed to ensure fast, reliable feeding. It’s short tube places the hopper much closer to the center of the ’gun for better side-to-side balance with a full hopper. The powerfeed block is a separate piece that slides into a slot in the ’gun body and is fixed in place with a pair of screws. The ability to remove the powerfeed makes between-game cleaning of the feed and breech much easier if you ever chop a ball. Though this is much better than older Micromags where only a single screw held the powerfeed on, I still found the pair of screws to occasionally come loose during a game, resulting in a wobbly feeder. A couple drops of loc-tite on the screws should prevent loosening if this becomes a consistent problem.

The top of the body has an integral sight-rail which is, naturally, completely obscured by the powerfeed. Unless you use some very tall mounts, the only sight you’ll be able to use with this ’gun is the Armson sight which uses an optical illusion to superimpose a red dot rather than requiring you to see through the sight.

The Micromag body has a mount for a vertical ASA or forgrip just in front of the trigger guard. This is not a standard AGD vertical mount, though. Due to the very small size of the ’gun and the built-in rail, Pro-Team had to devise a different way to mount them. As a result, only Pro-Team’s own verticals and forgrips can be mounted on the Micromag. The gas-through forgrip that comes with the RetroMicromag Plus is nicely rounded and finger-grooved to provide a comfortable and stable grip.

The .45 frames that come on Micromags are made for Pro-Team by Benchmark. The two-finger trigger frame that was installed on the Micro sent to me is a $40 upgrade option when the ’gun is purchased. Separately it costs $84.95. The .45 frame itself makes the trigger pull a bit softer by putting the contact point of the sear rod closer to the pivot point than on stock Automags and RTs. The two-finger trigger makes it even easier to shoot fast. There is a lot of slack in the trigger pull both in front of and behind the point where it fires. Frankly, I think this frame needs a trigger stop. The way it comes stock, the trigger feels long, boggy, and not as responsive as one might hope. With a stop screw installed, this trigger takes on an entirely new feel, becoming short, snappy and much more responsive. Please note: any modifications should be carried out by trained airsmiths.

A nice feature of this two-finger frame is that there is a full 2-finger guard around the trigger. Pro-Team considers this to be an extremely important safety feature and will only honor the warranty on paintguns with intact trigger guards. What is rather bothersome is that you can only shoot with two fingers. That’s all well and good when you’re just trying to shoot fast, but I find that I shoot much more accurately when I fire with just one finger and grip with the rest. There is simply nowhere comfortable to rest your middle finger other than on the trigger.

A set of custom, laser-cut Pro-Team rubber wrap-around grips complete the setup and provide a comfortable, slip-free hold.

The barrel included with this ’gun was one of Armson’s new 13" Stealth barrels. Like the original Armson barrel, the Stealth barrels still have the progressive internal rifling which, despite what its spiral-pattern might suggest, is supposed to prevent the ball from spinning. The Stealth barrel differs from older Armsons by adding several rows of ports along the exit-half of the barrel’s length. One well known fact is that old Armson barrels were the loudest barrels in existence. These ports reduce the noise level of the Armson Stealth down from the original Armson’s loud bark to a quiet whisper.

One place where I am going to take Pro-Team to task is in the manual. Airgun Designs has always offered exceptional manuals and videos with their paintguns. With them, any player, however novice, could quickly and easily learn how to use, maintain, and troubleshoot their Automags.

The original Micromag came with an Automag manual with a "Micromag" cover stapled over it. While the AIR valve and troubleshooting information were largely the same between the two, I felt that the presence of Automag-specific diagrams and the complete absence of Micromag specific information was a real drawback.

Bad as that was, the RetroMicromag’s manual situation is even worse. Pro-Team included the same Micromag-covered Automag manual in the box. I can’t imagine what their rationale for this is. Not only does this still not have any Micromag-specific information, but the valve is completely different now as well. There is absolutely no information in this manual that has any pertinence to the ’gun it was packaged with. Any new player trying to make sense of this paintgun using that manual would become hopelessly confused within minutes. Since neither the RT manual or video is included, the player is left with no useful operating, maintenance, or troubleshooting information whatsoever.

Fortunately, Pro-Team is working on new Micromag and RetroMicromag manuals of their own. Considering how long they’ve been selling these paintuns, I don’t think I’m being at all unfair in saying that these are way overdue. I’ve seen an early draft of one of these and it does look promising. Once they are available I’ll withdraw this reservation.

The MicromagRT in Play

So, when it’s all said and done, how does it shoot? No surprises here. It shoots like an Automag RT. The reactive trigger works impressively, jumping back against your fingers after each shot and never starving out. Want more kick-back in your trigger? Just turn up the input pressure and you’ve got it. Some people report being able to get the trigger into a "sweet spot" where all you have to do is hold the trigger back at a certain spot and allow it to simply bounce off your fingers and fire, for all intents and purposes, full auto. I didn’t try this. Frankly, I don’t like the idea. As I mentioned earlier, I don’t like breaking paint in the ’gun. Going full-auto in an unlimited, gravity-fed paintgun is, in my opinion, asking for trouble.

With the reg set behind the grip and the hopper situated right over the trigger, the Micromag is very well balanced when loaded –particularly important in a paintgun this light. Its compact size made cramped front bunkers a bit more tolerable than with larger ’guns.

The RetroMicromag’s efficiency is acceptable, but not exceptional. I was getting somewhere around 800-900 shots from a 68 ci 3000 psi nitrogen system. Velocity consistency was also good, staying within a 10 fps range with good, round paint.

Accuracy, as with all paintguns, was heavily dependent on the paint and barrel. I suspect that the Zap I was shooting was a bit too big for the Armson Stealth. I was getting decent range and accuracy, but I was still breaking more paint than I like to (something like 2 or 3 breaks per game). After a break, the Armson is a nightmare. The next group of shots come out of the barrel like hummingbirds on heroin, hooking, dipping, and corkscrewing off into the distance. I was surprised to find that the accuracy leveled back out again after putting 20 or 30 shots through it. Nice as that is, if you shoot an Armson, you’ll probably want to carry a good stick squeegee to speed up the process. When I switched to my larger-bored LAPCO BigShot barrel, things became much nicer. I only broke a ball every 2-3 games, it cleared faster, and accuracy improved marginally.

Conclusions

In all honesty, I came to the conclusion a long time ago that I’m just not an Automag guy. I break too much paint in them and it just ends up frustrating me. I know that it is not an inherent fault of the ’gun because I’ve seen a lot of superb players using them extremely effectively. Pros with RTs are more dangerous to their opponents yet.

But even with my unfavorable history, I found the RetroMicromag to be a lot of fun to play with. I really liked the compact size, light weight, and excellent balance. The reactive trigger is also a huge improvement over the original Automag and makes shooting the ’gun a real pleasure. The milling is clean, sharp, and eye catching. The anodizing is bright and lustrous, of a very high quality and extremely durable.

Pro-Team deserves to be commended for the excellent job they’ve done improving and modernizing the Micromag’s design over the years. The only real significant problem has been not getting together a proper manual for this ’gun until just now.

At only $749.95 for the single-trigger RetroValve Micromag ($789.95 for the 2-finger variant) it’s not all that much more expensive than the standard Automag RT, and comes out as a good value given how much more it offers in standard accessories and cosmetics. Base model RetroValve Micro’s go out the door at only $649.95, so if you don’t need the cosmetic niceties or the forgrip, you can get it at an even better price.

All material at this site is © Ravi Chopra, 1999