I have been reading around about techt bolt modifications and so I opened this thread to see what people have done.
Here's what I have found in other threads so far:
For the G3 supposedly you can trim off .026" off the bolt tail and it will allow the spool valve to open a little earlier. Supposedly this will allow the gun to run at lower pressures (135-145psi) than the unmodified Techt bolt and with increased efficiency.
Can this also be done with the Techt G4 bolt? Has anyone tried it? What else have people done to their Techt bolts?
I know that you can sand/file down the bolt stop so that the bolt retracts a little further, but then Techt has already provided a slightly thinner bolt stop and shorter bolt so the bolt face clears the breach more. If your Techt bolt protrudes into the breach too far and causes balls to not drop fully into the breach, contact Techt for their shorter bolt and bolt stop. If you do shave down your bolt stop beyond the point where the back of the bolt hits the back o-ring inside the gun then the bolt will slowly chew up that o-ring. So the idea is to shave back the bolt stop so the bolt stops just short of the back o-ring.
I have a longer/old revision of the techt bolt for the G4 that causes ball/breach jams. I will take down the tail a little and also take a little off the back of the bolt to see if I can get it to clear the breach better.
Lowering your G4 or G3 Techt operating pressure bolt tail MOD:
You need to carefully file off a very small amount of the tail length. Dont scratch the tail with the file! Take off a little tiny bit at a time and then test fire the gun. You don't want to be blowing air back up the feed neck by having the spool valve open too soon. Before you begin attach the barrel, air up your gun, turn off the eyes and lay a tissue over the feed neck. Fire the gun. The tissue should not blow off the feed neck because 100% of the air is going down the barrel. If you shorten the bolt tail too much, the spool valve will open too soon and you will waste air by blowing it out the feed neck rather than down the barrel. Since the spool valve will be open longer, dwell can probably be lowered a little.
My DP G4 Techt bolt tail mod:
******If you want me to do this for you...http://www.pbnation.com/showthread.p...75990191******
I did the bolt tail mod and I have to tell you that I went a lot further than the .026" (.077" when I finally stopped) and never got to the 140psi operating pressures that others have gotten. That's not to say I didn't see improvement. With the stock bolt my G4 needs 200psi to get 280fps. With the unmodded Techt bolt it needs 180psi to get 280fps. With the modded bolt tail as it stands right now (see below for details) it needs 160psi to get 280fps. Since I incrementally went beyond the .026" in 3 steps I tested FPS at each step of bolt tail length removal. I can say that with each step my velocity continued to go up indicating that less air pressure was needed to fire at 280fps.
What I did:
Note: I used the same tank, barrel, gun, lube, loader and paint balls (Premium brand) for all my tests to eliminate as many variables as possible. I never touched the regulator screw after chronoing with the unmodded bolt to 280fps so that any changes had to be from the bolt tail mod.
1. I measured the bolt tail before starting with my micrometer (see below pictures) to find it's length. Then I marked off that magic .026" with a sharpie.
2. I took a 2" long piece of 3/8" dowel and wrapped masking tape around one end until I had more tape diameter than the inside diameter of the bolt front. Then I tore off 1" sections of tape until the dowel and tape diameter were a really snug fit in the bolt front. This allowed me a secure way to hold the bolt in the drill press. The bolt slides over the tape on the dowel and the bare wood end of the dowel is clamped in the drill chuck. This kept the bolt secure on the drill without any chance of damage to the bolt surfaces.
3. Next I ran the drill press at its fastest speed and used a very fine file to shorten the bolt tail length to the .026" mark.
4. Then I used a diamond sharpening stone to "finish" the grind off and to put a new bevel on the bolt tail.
5. Next I slid the bolt off the dowel/tape and hand rounded and beveled the end a little more if needed with the diamond stone.
5. Then I carefully cleaned out every tiny glittering speck of aluminum from off the bolt.
6. Since the bolt was now completely clean, it needed new lube so I put a thin coat of Militia Lube on the tail, bolt o-ring and on the bolt front. I attempted to be as consistent as possible with my application of lube so that too much or too little lube wouldn't be a variable.
7. I put the modded bolt in the gun, turned on the air and fired 20 shots or so over my chronograph. The .026" mod gave a slight increase in FPS (280 to 290 at most). It was hard to be sure since these guns aren't the most consistent.
8. I then put my unmodded bolt back in just to be sure there was a difference and I could see that I was getting about 8-10fps increase with the modded bolt.
9. Since I had already gone to the .026" mark, I went another .026" and repeated steps 3 through 6.
10. This time the gun was shooting consistently over 300fps with no regulator change or adjustment.
11. I then took off another .026, repeated the above steps and was chronoing in the 310+fps range. Considering this was a first attempt and that I had gone 3 times further than the magical .026" I decided to stop and do more tests. See the below pics. They speak volumes!!!
Techt bolt measured for the original .026"
Unmodded Techt bolt tail length
Modded Techt Bolt tail length after taking it down 3 times
Comparison of unmodded and modded bolts. You can see the length difference.
FPS with unmodded Techt bolt. Once I set the reg screw I never touched it again until I was ready to chrono with the modded bolt at 280fps so I could determine the new reg output pressure at 280fps. Look at the time in the lower left corner of the display. You can see that there is just a couple of minutes difference between this picture and the next picture. I had just enough time to swap the unmodded bolt with the modded bolt and chrono again. Obviously I checked the FPS with the stock bolt again after modding the other bolt. The gun was still shooting in the low 280's just like it was before I started.
Final FPS after 3 removals of bolt tail length. I did 20+ shots over my chrono and they varied from 309 to 321 so 317fps is kind of in the middle of that range. Again the regulator was never touched during these tests.
As you can see this is a legitimate mod. The pictures don't lie! I will take the bolt tail down further on another day. I'm fairly certain that I haven't reached the minimum bolt tail length yet. I haven't done any efficiency tests to see if that has changed. In the past with the Techt bolt I typically got around 800 shots on 3000 psi in a 68/4500 tank. My field doesn't have 4500psi because some dumb -ss blew himself up by filling his 3000psi tank to 4500psi!
Make your own pressure tester:
I found a small tapping kit for 1/8" NPT threads at the local hardware store for $10. It included a drill bit and 1/8" NPT tap. The first thing I did was drilled out the allen hole in the back cap just about 1/2" deep with the drill bit that came in the 1/8" NPT kit. You don't want to go too deep or you will compromise the strength of the stem. Then I used a 1/8" drill bit to go deep enough to meet up with the hole in the side of the back cap stem. The hole in the stem is 1/16" in diameter and goes through half way. Drilling and tapping the back cap requires a fair bit of torque and so you will need to hold the back cap in some way that doesn't damage it. My solution was to take a 5" long piece of pine lumber and drill a 1" diameter hole in the center of it. I then broke it in half along the grain. Then I put the back cap in the hole and clamped the two halves of wood around the back cap with a vise. When you thread the gauge into the back cap orient it so that when the back cap is fully screwed into the gun that the gauge is right side up. Use some blue locktite on the gauge threads to seal them and to keep it from turning in the back cap. You can now use the gauge instead of an allen wrench to remove the back cap. This MOD could be done to the Techt back cap too, but be much more careful since there is less material to work with.