It is best if you understand trigger work and have a decent understanding of what you are doing. Attempting this modification may result in damage to your Neos if done wrong, or even by doing what I advise. There is also the possibility of your Neos malfunctioning due to an improper install or adjustment which could result in full auto fire, damage to property, serious injury and or death.
You will need two set screws, a twist drill (aka drill bit), a hand drill (electric not recommended, a tap wrench will work just fine), a file/sandpaper or something to shorten the smaller set screw a tiny bit if required, "gun-tite" or blue loc-tite is optional and probably not needed. These are available at any hardware, or home improvement store. I suggest two metric 8-32 sized set screws and the matching #29 twist drill. One set screw should be 1/8th of an inch long, and the other a 1/4th.
Taking the Neos apart
To do this you should first field strip the Neos. Then remove the grip, slide latch (the thing that holds the slide open) while being careful for the tiny spring that likes to jump out, and finally the firing pin block. Remember to take out and not loose the sear spring, and it's two guides.
Installing the set screws
You will have to drill one hole in front of the black trigger bar, it is the set screw with the blue gun-tite in the picture below. You want the hole to be square/parallel with the frame when viewed front to back, but at a 45 degree angle give or take if viewed from the side. The pictures help explain it.
You should have the sear support block already out, so rotate the trigger linkage to the front, the spring may have already done that for you. Push the drill into the corner, you want to drill into the front wall and go down at as shallow of an angle as you can without the drill touching the trigger bar. Drill 3/16ths of an inch through, you should not cut into the hole that the grip goes in to, if you do it is no big deal. If you did it right the set screw will be on the left side and when the trigger comes down will hopefully not brush against the corner of the set screw. Ideally you would want them to hit squarely, but that may not be impossible with the trigger in the way of the drill, and later the Allen wrench.
The shorter set screw will also be aimed at the same trigger bar. This time you will go in through the magazine well. The hole should be made on the left half, with about an 1/8th of an inch of plastic above the top of the hole. Drilled all of the way through until it hits the trigger bar, do not worry you can not hurt it. I had to file the head of the set screw a bit with a cloth file because it stuck out a tiny bit into the magazine well. I also used a small razor blade to cut the plastic lip off that the drill created.
Notes, and theory
If you look at the left side of the pistol you will see a pin that the trigger pivots on, both set screws will be above that to control travel. Basically this stopper holds the trigger against/close to the sear, but does not move it.
Your drill will cut through the frame like a hot knife through butter, be careful on the front set screw so that you do not cut into anything or any opening. I doubt you would damage anything, but still.
You will have to do a thorough cleaning of the trigger area by the spring because the plastic causes it to feel gritty if not cleaned out.
Another thing I fixed today was the slight amount of play in the front of the trigger guard. I used a soldering gun and lightly ran it up and down the male barb to melt a few ridges, then sanded them down a little so they fit smoothly and snugly. I no longer have any play in the front, it bothered me that my finger could move it a bit before.
The front set screw I tried doing by burning it in. That has worked very well for me in harder plastic, but in the Neos just use a drill bit and preferably a hand drill. The front set screw in the picture is a 6-32 size, if it does not work out for me I will replace it with the recommended(by me) 8-32 size with a drilled hole. I had to use loc-tite due to my burned hole not working out very well. I am guessing that Beretta used temperature resistant plastic because of barrel heat.
I know this article is pretty bad right now, but I just made it today(11-15-03) by cutting and pasting posts I made at www.rimfirecentral.com and throwing some pictures together.
These instructions for the Neos work for pretty much any fire arm, or paintball gun, I have more gun tips to share soon.
Basic tuning is as follows, adjust the rear(magazine well) set screw so there is a tiny bit of trigger movement when the gun is cocked and ready to fire. Use snap caps to test it, not live ammo. The front one you set so that it dry fires(use snap caps or emply spent casings) with less than 1/64th of an inch between the trigger bar and the front set screw. That 1/64th is your saftey margin to make sure no matter what it fires reliably. Another way it to see how far you can get it to barely fire reliably each time and then go an extra 3/8ths of a turn for good luck and a margin of error. I will post more theory later.