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Auto/Mini/Micromag Trigger Job
© Ravi Chopra, 1996

Enough people have been asking me about this, it's short enough, and it looks like the Micromag Infosheet is going to be a while coming, so I figured I'd just crank it out. It's been a while since I offered anything really new. Let me know if you like it and let me know how it works out for you.

These techniques are effective in reducing the trigger pull force and length of the Automag, Minimag, and Micromag, as well as reducing the amount of velocity drop-off that is commonly associated with rapid-fire. Micromags and other 'guns with '45 grip frames will see slightly better results due to the slight difference in sear-trigger interface.

Oh, and of course the quick disclaimer. These are just a bunch of things I do. I am not suggesting you try any of this stuff. If you do and screw your 'gun up, don't blame me!


Read this first!

This is very important. If you do decide to try any of these 'mag trigger-job techniques, start out doing them in moderation. You can always grind or polish more off later, but you can't put the metal back. If you do shave off too much, you're going to end up with a paintgun that doesn't work and you'll have to replace the parts you overground.

Before you start, you're going to need some sort of grinding/polishing tool. I use a Dremmel with a variety of grinding and polishing heads. A file and sandpaper will work just as well, but will take much more time and energy.


Technique #1: Sear Polishing

This is probably the most common technique used in 'mag trigger-jobs. It entails reducing the height of the front part of the sear that catches the bolt. By polishing it down, you reduce the distance the trigger needs to be pulled to release the bolt and fire the 'gun.

Look at the top of the sear, the long front part that rises higher than the rest of the sear and has a sharp back edge that catches the bolt is what we're interested in. On a new or only slightly worn sear, you'll see lines running horizontally across the top of this part. These lines are just remnants of the sear's production and are not important for the functioning of the sear. They are usefull as a gauge of polishing depth. Use your polishing tool to evenly polish down the top of the sear until these lines just disappear. Now put the sear back in the 'gun and try it out.

I know this does not sound like you're taking very much off, but it does make a significant difference in shortening and lightening the trigger pull. If you're still not happy with it, you can start grinding more down. Keep in mind, though, that if you take too much off, you'll ultimately end up with a 'gun that will either go full-auto much too easily or have chronic barrel leak. If you do take it down too far, you'll have to replace the sear.


Technique #2: Sear Beveling

Sear illustrationI only learned of this one myself recently. It is considerably more extreme than polishing the top of the sear and it leads to much faster sear wear. But when it's done right, it effects a much better improvement than polishing the top of the sear alone while retaining greater reliability. If you plan on doing this modification, only polish the top of the sear lightly. Significant grinding prior to beveling will definately lead to problems.

After polishing the lines out of the top of the sear, take your grinding tool and grind down one side of the sear top so that rather than being flat, it slopes down to one side. That is to say, it should slope down from left to right, or right to left, not front to back or back to front. You don't have to grind it down very much. 5-15 degrees should be sufficient. Make sure to leave one side at the original height to give some leeway for initial wear which will be rather quick when you first use it.

What this seems to achieve is to allow the sear to slip off the bolt more easily leading to a softer, less abrupt trigger pull.


Technique #3: Polished On/Off Pin

On/off pinOne of the most common complaints about the Auto/Mini/Micromag series of paintguns is velocity drop-off during rapid-fire. One way of alleviating this problem is to have the on/off valve open earlier in the trigger release so it is open longer between fires. One way to do this is by slightly shortening the on/off valve pin.

This modification must be done very conservatively and carefully to prevent mistiming the 'gun. If you make the pin too short, it will start opening before the sear has had a chance to catch the bolt and you will experience frequent bolt-stick. It is also important that you work on the bottom of the pin only, where it interfaces with the back of the sear. If you modify the top part that actually has to seal the valve, it will sometimes stick in the teflon o-ring.

Look at the bottom of the on/off pin. You should see shallow concentric circular grooves remaining from the pin's production. Polish the bottom of the pin until these grooves just disappear. Here more than anyhwere, be careful not to take off too much metal!

After putting the pin back in your 'gun, you should find that the air chamber refills earlier in the trigger release than with the stock pin. This allows it more time to refill between shots and thus reduces walk-back.


Technique #4: Free-Flow On/Off Valve

Old on/off valve topThis modification also helps to alleviate drop-off. It's so simple to do, I find it amazing that people spend $15-$20 to buy this when a $2 pin file and 10 minutes of work allow you to get the same effect.

Remove the brass on/off top from the on/off valve. If you have a stock valve, you'll find that the top of it (the part that sits against the o-rings at the top of the 'gun) is flat except for the hole the on/off pin goes through. The trick here is to use a small, fine file or grinding tool to cut thin channels from the center hole to the edges of the brass top. I like to cut them in a simple "X" shape intersecting at the hole. Then continue these grooves down the sides to meet the narrower bottom part of the piece.

These channels allow an easy path for gas around the valve from the point where the valve opens. When you put the 'gun back together, you should find that it recharges quite a bit more quickly than it did before and drop-off is reduced.


Technique #5: Adjust Sear Rod Length

The sear-rod couples the sear to the trigger. It is attached to the sear by threading into an arm that swings freely on the sear. Screwing the rod in or out of this arm adjusts the trigger position where the 'gun will fire. Keep in mind that for the most part this does not change the length or force of the trigger pull.

If you unscrew the rod enough, though, it will eventually get to a point where when the trigger is at the fully-forward position, the sear is still pushed back some. This effectively shortens the trigger pull some by "taking up the slack" inherent in the Automag trigger system. You typically do not use this with any of the first 3 techniques described here because it is very difficult (or impossible) to get them to work together reliably. The advantage of using this one is that it doesn't require any polishing or grinding and is easy to undo.

For Micromag users, you've undoubtedly found that the one thing the Micro lacks that it really needs is a trigger stop. You can just glue something into the space behind the sear to limit it's travel, or you can use this technique! If you shorten the trigger pull enough with the first 4 techniques, you can use this one to move the fire point forward of the point where the annoying safety stops the trigger. Do that and the safety becomes a trigger stop! Cool!


Technique #6: Pro-Team Products Power-Tube Spacer Kit

Power tube spacersI didn't believe this one until I tried it myself, but I am now convinced that if you're going to spend money upgrading the trigger of your 'mag, this is the first, best way to spend it.

The power-tube spacer kit consists of five color-coded aluminum cylinders of slightly different lengths. What you do is replace the power-tube spring with the longest one of these aluminum spacers. If you then have leaking down the barrel, go to the next shorter spacer. If it still leaks, go to the next shorter spacer, etc., until there is no leaking down the barrel. You will find at this point that your trigger has magically become much lighter and faster than it was before!

The way this works is by precisely setting how far back the power-tube o-ring is set. The stem in the middle of the bolt goes down the power-tube and seals against the o-ring. If your power-tube spring is too long, the o-ring is pushed too far back, you don't get a good seal, and the 'gun leaks down the barrel. If your spring is too short, the o-ring sits far enough forward that it catches the bolt-stem tightly and you get bolt-stick, slowing and stiffening the trigger pull. By finding the spacer length that sets the o-ring at the point where the stem just seals agaist the o-ring without sticking in it, you get a much lighter and quicker trigger pull.

The real beauty of this kit is how well it works with any 'mag with any trigger work. If you have stock trigger parts, it will make the pull lighter and faster. If you've done the modifications I describe above, or have had other work done to it, you will find that the trigger works even better after installing the correct length spacer.


Well, that's it. Good luck everybody. Let me know how the triggers work out for you!

All material at this site is © Ravi Chopra, 1999