A Glock, you can dremel no problem. I've done it. You could take 1/10" off every single surface, and it would still work.
What I did is dremel off some metal from the tab on the trigger bar, which engages the connector, to eliminate overtravel. Just makes more sense to me than putting in a screw, pin, or tab to make the trigger not go back as far. Then if the mechanism gets too dirty, the gun won't fire at all! But with the tab ground down, dirt will just bring the overtravel back.
What I recommend doing to a Glock is just lightly polishing, by hand, every single surface which rubs together on the inside. Use a hard Arkansas stone, as has been recommended, or perhaps a piece of leather or a rag with some metal polishing paste on it. That's really all it needs.
But if you want to totally change the feel of the trigger, you can also get different connectors, trigger springs, firing pin springs, and grind some other parts. Just don't try to shorten the pull to less than about 3/8", measured at the tip, or the drop safety becomes very iffy. And the firing pin safety wouldn't be much help if the gun is dropped, since the trigger spring will pull the trigger back, quite possibly faster than the striker falls.
If you want to improve the "crispness" of the break a tiny bit, you can grind down the hood of the striker (the part that the trigger bar cruciform pushes). When viewed from the bottom, barrel facing directly away from you, it's the top right corner you want to grind down, at a 45 degree angle, until the face of the hood (where the cruciform contacts) is about halfway gone. So when viewed from the bottom, instead of a square, you've got a square with the upper right corner missing. This helps because the trigger bar torques to one side. I can take a pic if you want to see exactly what it should look like.
To reduce the transition between takeup and break, you can drill a 1/16" hole in the trigger bar, right above the existing hole where the trigger spring attaches. Try to get it pretty close, so the thickness of the metal between the holes is the same as the amount of metal between the original hole and the bottom. By attaching the spring to the new hole (the end of the spring goes through the original hole, instead of dangling out the bottom), you reduce the upward force exerted by it, thus lowering the break weight without affecting the takeup weight much. And you can always attach the spring to the original hole again. Once again, I can do a pic if you like.
If you want a revolver-like trigger, you can get an NY-1 trigger spring, a 3.5 pound connector, and an increased power striker spring. I recommend removing the metal spring from the NY-1 housing, so that all you have is the plastic part. This setup will give you around a 6 pound takeup, 8 pound break. I've fired a few hundred rounds in exactly that configuration on my Glock 23 (plus the ground down striker hood), no problems. Probably one of the best possible "combat" trigger jobs you can do, if you also shoot wheelguns. And because it uses the NY-1 trigger spring, you don't have to drill a hole through the diamond-hard trigger bar.
If you want the trigger to feel like a
true two-stage single-action trigger, I recommend an 8 pound connector, increased power trigger return spring, and the hole drilled in the trigger bar. In this configuration (plus the increased power striker spring, which I wouldn't recommend for a two-stage feel), my gun has a 2 pound takeup and 6 pound break. I estimate with the regular striker spring it'd be 1 pound takeup and 5 pound break probably. Or if you'd rather have a heavy single action trigger, skip drilling the hole and you'll have about a 7-9 pound break or so, same takeup.
The other guns, I don't know nothing about.
He put a mag in the gun, racked the slide, pulled the trigger and it fired 7 times before it stopped. Put another mag in & 5 rounds later, he put it down and never fired it again....I think it still sits in the back of his safe 
