G&G GC16 Upgrade Issue, 420fps -> 290fps.

[d.j]

Hi All,

I have a G&G GC16 that I bought about a year and half ago. When I purchased the gun, literally the day, it was shooting 420fps with .2 gram bb's. Though after extensive testing, hundreds of dollars in parts :banghead: :banghead::banghead: , and successfully rebuilding another gun; I think mine is flawed.

I only recently bought a chrono, but I think the gun settled from 420fps to roughly 350fps and a continual decline has happened. I haven't been able to monitor it, because I've been steadily adding parts that would make the fps jump by 10 here and there.

Anyway, I did a lot of testing, and searching (especially here, and I have to say, ASC is one of the best and most helpful forums on the internet) to find my issue. I documented everything I did, so nobody thinks I'm crazy. Hopefully with my findings an experienced gun tech can make sense of it, because I really cant.

G&G GC16 Rebuild:

Brand New:
*420fps* <— Goal, closest was 385fps with m115.
Stock re-chrono with everything factory on June 21st, 2015 was *290fps*

*Unrelated mods include: Mosfet hard wired, deans connector, new trigger switch with silver wiring to fuse, (stock from fuse to mosfet), 11.1v lipo battery, Corrected AOE with sorbo pad (3/16 40 thickness) *

*All chrono results taken over 10 shots, with the hop-up incased in the upper receiver in the OFF position, using Evike .20g BB’s with the stock magazine and the above non-related mods, on an Xcortech X3500 at approximately 75 degrees Fahrenheit*

*All pre-testing is done with finger held over outlet nozzle to locate air leaks, as well as cylinder port for the cylinder to piston head test. Otherwise it’s left open*
*All testing is done using the gear box shell, with tappet plate and tappet plate spring*


TEST 1:

Pre-Notes:
-Stock spring is warped, and not perfectly straight. Therefore it’s safe to assume fps loss is definitely happening because of it, the questions is how much.

Parts:

Stock Piston + Piston Head
Stock Cylinder + Cylinder head (No teflon)
Stock Air Nozzle + Tappet Plate + Spring (Nozzle glued to tappet plate, half of air nozzle ring broke)
Stock Barrel 363mm
Stock Hop-up + Bucking (No nub for test)
Stock Spring Guid
Stock Spring
Stock Motor + Grip
Stock Gears (Re-Shimmed)
Stock Gearbox Shell
Stock Gearbox Screws
Stock Bushings
Stock AR Latch + Spring
Stock Trigger + Spring
Stock Safety Switch + Spring
Stock Cutoff Lever + Spring

Pre test compression:

1. Cylinder to piston head
- Perfect

2. Cylinder to air nozzle
- Perfect

3. Piston to cylinder
- Leaking, decent at times, but can always be pushed fully to cylinder head

4. Piston to air nozzle *Extended*
- Pretty good, 8/10. Strong resistance, but successfully goes all the way to the cylinder head.

5. Piston to air nozzle *Closed*
-Decent compression, 7/10. Resistance but successfully goes all the way to the cylinder head.

6. Hop-up to barrel
- Completely leaking around bucking.

7. Piston to barrel
- 6/10, Sounds like leaking from air nozzle to bucking.

Chrono Results:
1. 310.3
2. 311.6
3. 311.4
4. 309.6
5. 311.1
6. 309.9
7. 308.4
8. 312.7
9. 309.6
10. 309.1

Average:
310.3fps, 4.3fps variance.

Notes:
- Lubricated gears with concentrated silicon oil
-Sounds like its short stroking and not completing a proper cycle.
-Could be the sorbo pad cutting into valuable air volume.
-Piston head, hop up, and bucking all have compression loss.
-Took an in-depth look at the hopup chamber and noticed a port in front of the feed port, which allows air to escape. How much is unknown.

TEST 1B:

Pre-Notes:
- Going to create a perfect seal from hop-up to barrel, without disassembling gear box to see if that’s the problem.
-Going to swap hop-up to G&P full metal one, with stock G&G green bucking. This hop-up has no port before the feed port.

Parts:
Stock Piston + Piston Head
Stock Cylinder + Cylinder head (No teflon)
Stock Air Nozzle + Tappet Plate + Spring (Nozzle glued to tappet plate, half of air nozzle ring broke)
Stock Barrel 363mm
G&P Metal Hop-up + Stock Bucking (No nub for test)
Stock Spring Guid
Stock Spring
Stock Motor + Grip
Stock Gears (Re-Shimmed)
Stock Gearbox Shell
Stock Gearbox Screws
Stock Bushings
Stock AR Latch + Spring
Stock Trigger + Spring
Stock Safety Switch + Spring
Stock Cutoff Lever + Spring

Pre-Compression test:
1. Hop-up to barrel
-Perfect

Chrono Results:
1.323.1
2.324.9
3.324.3
4.325.5
5.325
6.324.4
7.324.3
8.324.8
9.323
10.320.7

Average:
324fps, 4.8fps variation

Post-Notes:
-Suffice it to say the stock hop-up in this setup was robbing the gun of on average 13.4fps.
-All testing from here forward will use the G&P metal hop-up chamber.

TEST 1C:

Pre-Notes:
-Going to put the prometheus 6.03 tightbore barrel into the G&P metal hop up to see if any more fps is acquired.

Parts:
Stock Piston + Piston Head
Stock Cylinder + Cylinder head (No teflon)
Stock Air Nozzle + Tappet Plate + Spring (Nozzle glued to tappet plate, half of air nozzle ring broke)
Prometheus 6.03 Tightbore Barrel 378mm (+15mm to stock)
G&P Metal Hop-up + Bucking (No nub for test)
Stock Spring Guid
Stock Spring
Stock Motor + Grip
Stock Gears (Re-Shimmed)
Stock Gearbox Shell
Stock Gearbox Screws
Stock Bushings
Stock AR Latch + Spring
Stock Trigger + Spring
Stock Safety Switch + Spring
Stock Cutoff Lever + Spring

Pre-Test Compression:
1.Hop-up to Barrel
-Perfect

Chrono Results:
1.336.5
2.332.9
3.330.9
4.333.5
5.332.4
6.333.7
7.332.4
8.333.4
9.332.5
10.332.4

Average:
331.1fps 5.7fps variance.


Post-Notes:
-Switching to the prometheus barrel increased average by 7.1fps.
-Externally the gun is sound, now it’s time to get into the internals.
-All testing will consist of the prometheus tightbore barrel from here on out.


TEST 2:

Pre-Notes:
-Going to start simple by teflon taping the cylinder head to try and boost internal compression.
-As well as change the piston head o-ring.

Parts:
Stock Piston + Piston Head (G&P o-ring)
Stock Cylinder + Cylinder head (Teflon)
Stock Air Nozzle + Tappet Plate + Spring (Nozzle glued to tappet plate, half of air nozzle ring broke)
Prometheus 6.03 Tightbore Barrel 378mm (+15mm to stock)
G&P Metal Hop-up + Bucking (No nub for test)
Stock Spring Guid
Stock Spring
Stock Motor + Grip
Stock Gears (Re-Shimmed)
Stock Gearbox Shell
Stock Gearbox Screws
Stock Bushings
Stock AR Latch + Spring
Stock Trigger + Spring
Stock Safety Switch + Spring
Stock Cutoff Lever + Spring

Pre test compression:

1. Cylinder to piston head
- Perfect

2. Cylinder to air nozzle
- Perfect

3. Piston to cylinder
- Leaking, can be pushed all the way.

4. Piston to air nozzle *Extended*
- Leaking.

5. Piston to air nozzle *Closed*
- Leaking

6. Hop-up to barrel
- Perfect

7. Piston to barrel
- Leaking.

Chrono Results:
1.331
2.328.5
3.329.4
4.330.3
5.328.6
6.328.8
7.330.9
8.330.5
9.329
10.330.1

Average:
329.6fps, 2.8fps variance.

Post-Notes:
-More consistent than previous test, but still low.
-Consistency is odd, considering the air leak from the piston to cylinder and forward.
-Next test will most likely consist of a perfect air seal piston head, to try and regain the lost air. That will hopefully give a bump in fps.

TEST 3:

Pre-Notes:
-Going to swap the piston head, with a Guarder ball bearing one, to see if I can regain some of the obvious loss in compression, then i can continue troubleshooting from there.

Parts:
Stock Piston + Guarder Ball Bearing Piston Head
Stock Cylinder + Cylinder head (Teflon)
Stock Air Nozzle + Tappet Plate + Spring (Nozzle glued to tappet plate, half of air nozzle ring broke)
Prometheus 6.03 Tightbore Barrel 378mm (+15mm to stock)
G&P Metal Hop-up + Bucking (No nub for test)
Stock Spring Guid
Stock Spring
Stock Motor + Grip
Stock Gears (Re-Shimmed)
Stock Gearbox Shell
Stock Gearbox Screws
Stock Bushings
Stock AR Latch + Spring
Stock Trigger + Spring
Stock Safety Switch + Spring
Stock Cutoff Lever + Spring

Pre test compression:

1. Cylinder to piston head
-Perfect

2. Cylinder to air nozzle
- Perfect

3. Piston to cylinder
- Perfect

4. Piston to air nozzle *Extended*
- Perfect

5. Piston to air nozzle *Closed*
- Perfect

6. Hop-up to barrel
- Perfect

7. Piston to barrel
- Perfect

Chrono Results:
1.347.5
2.349.2
3.352.5
4.348.5
5.349.3
6.347.3
7.352
8.345.8
9.351.3
10.347.1

Average:
349.1fps, 6.6fps variance.

Notes:
-Gained 19.5fps by improving compression all the way through the gun.
-Last thing to test is the warped, worn spring. This may be the final key to getting this gun shooting good again.

[d.j]

TEST 4:

Pre-Notes:
-Going to swap springs to matrix M115 to try and find the missing FPS.
-Upon doing my pre compression test i noticed a leak in the air nozzle.
-It will only leak with the piston, not the blow test. Both open and close in the gearbox shell.
-Decided to switch to Hawk air nozzle, and guarder tappet plate instead to achieve perfect compression.

Parts:
Stock Piston + Guarder Aluminum Ball Bearing Piston Head
Stock Cylinder + Cylinder head (Teflon)
[Hawk Air Nozzle + Guarder Tappet Plate + Stock Spring
Prometheus 6.03 Tightbore Barrel 378mm (+15mm to stock)
G&P Metal Hop-up + Bucking (No nub for test)
Stock Spring Guide
Stock Spring
Stock Motor + Grip
Stock Gears (Re-Shimmed)
Stock Gearbox Shell
Stock Gearbox Screws
Stock Bushings
Stock AR Latch + Spring
Stock Trigger + Spring
Stock Safety Switch + Spring
Stock Cutoff Lever + Spring

Pre test compression:

1. Cylinder to piston head
- Perfect

2. Cylinder to air nozzle
- Perfect

3. Piston to cylinder
- Perfect

4. Piston to air nozzle *Extended*
- Perfect

5. Piston to air nozzle *Closed*
- Perfect

6. Hop-up to barrel
- Perfect

7. Piston to barrel
- Perfect

Chrono Results:
1.320.6
2.323.3
3.328.1
4.330.1
5.340.6
6.333.3
7.343.5
8.334.6
9.340.9
10.342.2

Average:
333.7fps, 22.9 variance.

Post-Notes:
-Although the compression was good in testing it, it obviously wasn’t in shooting. The FPS dropped by 7.
-Going to put the stock air nozzle back in, and regardless what the testing will show, it clearly isn’t the end all to be all.
-Going to do my original test idea of swapping springs to regain lost fps.

TEST 5:

Pre-Test Notes:
-Swapping in matrix m115 spring.
-After testing the stock nozzle, the compression is horrible, as bad as it was in test 1. There’s no way im going to put that back into the gun as that may be the variable. It was perfect, and now it’s leaking air like crazy. Even though I lost 7fps, i’m putting the hawk nozzle back in with the m115.

Parts:
Stock Piston + Guarder Aluminum Ball Bearing Piston Head
Stock Cylinder + Cylinder head (Teflon)
Hawk Air Nozzle + APS Tappet Plate + Stock Spring
Prometheus 6.03 Tightbore Barrel 378mm (+15mm to stock)
G&P Metal Hop-up + Bucking (No nub for test)
Stock Spring Guide
Matrix M115 Spring
Stock Motor + Grip
Stock Gears (Re-Shimmed)
Stock Gearbox Shell
Stock Gearbox Screws
Stock Bushings
Stock AR Latch + Spring
Stock Trigger + Spring
Stock Safety Switch + Spring
Stock Cutoff Lever + Spring

Pre test compression:

1. Cylinder to piston head
-Perfect
2. Cylinder to air nozzle
- Perfect
3. Piston to cylinder
- Perfect
4. Piston to air nozzle *Extended*
- Perfect
5. Piston to air nozzle *Closed*
- Perfect
6. Hop-up to barrel
- Perfect
7. Piston to barrel
- Perfect

Chrono Results:
1.372.3
2.380.7
3.360.3
4.355.1
5.364.3
6.377.1
7.351.6
8.380.7
9.379.6
10.374.1

Average:
369.6fps, 29.1 fps variance INITIALLY, then gun lowered itself to an average of 343.5fps with approx 60 shots through it, over the last 30 it has a variance of 11.9fps, with 348fps being the highest and 336.1fps being the lowest.

Notes:
-There must be something wrong in either the gearbox shell, or the body of the gun to allow such variance and the inability to consistently chrono over 350fps with any spring, piston head, air nozzle, tappet plate, hop up, barrel, and hop up bucking with perfect compression.
-The wiring also got really hot, as well as the motor.
-Maybe the higher fps unsettles something? Unsettled it can only shoot 350fps?
-The first 10 shots have a 29.1fps variance, but by 60 it dropped to 11.9, which is still a lot higher than any of the earlier tests.
-Potentially the way the spring guide sits on the shell, or moves, isn’t allowing.
-The variances could go on forever.

[Hectic]

Well it almost definately has to be an air leak somewhere. Most likely hop/rubber/barrel combo or the piston head/oring/cylinder.
only other thing i could think would be if the piston is getting hung up durimg its forward motion.

Edit: unless the spring is missing from the front of the hop up.

[Zfurlong]

If your using a flat hop, put Teflon tape over the end of the hop rubber. You'll regain some of the lost air doing that

[ThunderCactus]

Did you ever check your air nozzle alignment to the barrel?
Was a major issue with g&p and always resulted in a very consistent 50-80fps loss

And do a light test with the air nozzle forward and see if it really is sealing fully against the hop chamber

[lurkingknight]

have you not tried tightening the buffer tube screw too much? Overtightening of grip or buffer tube screws can result in pulling the gearbox down or cant it upwards at the front.