-FPS upgrade
-Accuracy upgrade
FPS upgrade
The first thing to consider about an FPS upgrade is that greater FPS doesn’t equal more range. It CAN, but it doesn’t always.
Here is a list of parts to consider for an FPS upgrade:
-Spring (This is the most obvious. Choose a spring from the spring chart that should put you in the FPS range you want. Keep in mind there are many variables to FPS other than spring, and the guide is just a starting point)
-Spring guide (if yours isn’t metal, you will want a metal one. A plastic spring guide will wear out with a stiffer spring.)
-Bushings (plastic bushings will wear out quickly with a stiff spring, causing a catastrophic gearbox failure. They are all basically the same except for ball bearing bushings, which allow your gears to spin more freely)
-Shims (not always needed, but sometimes you need to. Many guns come from the factory shimmed correctly, some don’t, and some need to be re-shimmed after significant use. If you change your bushings, you must re-shim)
-Battery (stiffer springs will require more juice. This varies by shimming, spring guide, wiring, and motor)
-Piston, piston head, cylinder(Not always necessary as many guns come with good parts here. If you are extending your inner barrel, you will likely need a different cylinder.)
-Gears (sometimes people want higher RoF, or tougher gears for REALLY high FPS, or helical gears because they are supposed to run smoother.)
-Gearbox shell (non-reinforced shells will warp or crack)
Each replica is different, so we won’t cover how to get to the gearbox in this guide.
Step 1:
Discharge your spring by firing in semi-auto. Disconnect your battery and strip your gun down to the gearbox.
TIP: Before opening the gearbox it helps to screw the long gearbox locking screw into the back of the box, this locks the spring guide in place and helps things no to go flying when you open it up. See Figure 2.
Step 2:
Open your box while holding onto the locking screw to keep things from going flying. Press down on the cylinder and slowly pull the spring guide and spring out.
Step 3:
Pull the old spring out. Most modern guns the spring will come right out, if it’s a gun with the spring held into the piston, pull out the screw on the piston head and the spring will come right out.
Step 4:
Replace the bushings if they aren’t metal. You’ll need to pull the gears and anti-reversal latch out to do this. Make sure not to lose your shims. You’ll need to re-shim the gearbox after replacing the bushings. See re-shimming guide.
NOTE: You may need to clean out the old lube and re-lube the gears if it is an old gearbox. Use alcohol to clean, and white-lithium to relube the gears. A very small amount is all that is needed. The piston/cylinder should be lightly lubed with 100% silicon gel.
Step 5:
With your gears and anti-reversal latch in place, put in the new spring and spring guide so it is not compressed. Press down on the cylinder and ease the spring into place, and the spring guide into the grooves to hold it in place.
Step 6:
While pressing down on the cylinder to hold the spring in place, place the other half of the gearbox shell into place. You may need to jiggle it around to get the gears and anti-reversal latch to line up with the holes.
TIP: Use a knife to move the gears into place to get the shell to fit.
Step 7:
Put your gearbox back into your gun and test fire. If this is a version 3 gearbox, you can test fire without putting it back into the gun.
Note: You may need to adjust motor height after this, see the motor height adjustment article.
Re-shimming your gearbox:
If you have an old gearbox, new bushings or are concerned that the factory didn’t shim your box well, you will need to buy a shim set and re-do it.
With your gearbox opened, remove the anti-reversal latch, spring/spring guide and piston. All you need in place is your gears, bushings and shims.
There is no magic formula for how many shims to use, keep in mind they come in different thicknesses.
With your shims in place, put the gearbox shell back together and put in two screws, at either end of the box. With an eraser tip pencil or your finger, reach in to the top of the gearbox and try to rotate the gears. See Figure 1.
If your box is over-shimmed, the gears will be hard to move or will be tight feeling, and it may be difficult to fit the gearbox into the gun body (as with Metal bodied M4/M16s)
If your box is under-shimmed, the gears will wobble. Wobbling gears wear out quickly.
If your box is shimmed correctly, the gears will move freely, but not wobble.
Accuracy upgrades:
Since each hop up unit and replica is different, we won’t go into how to disassemble each one. Instead we will discuss how the parts affect accuracy.
Parts to consider
-Inner barrel (A tighter inner barrel will allow the BB less “bounce” room going down the barrel, and will result in better accuracy)
-Hop up unit (A better hopup will provide better barrel fit, and less hop-up backoff)
-Hop up bucking (A better rubber will grip the BBs better and provide a more consistent backspin)
-Hop up nub (H-type nubs put straighter backspin on the BBs for flatter shots)
-Air nozzle (Smooth bore type air nozzles put a less chaotic burst of air behind the BB, so it bounces less down the barrel. Think of it like pushing a bb versus kicking it)
Notes on these upgrades:
-Putting a new air nozzle in requires opening up the gearbox.
-When putting a new hop up nub into your hop up unit, use a bit of chapstick to hold the nub onto the hopup arm while you assemble the unit
-Use 100% silicon spray to lube the bucking for insertion into the hop up unit.
-Soft type buckings are better for low-FPS guns and cold weather. For very high FPS guns, a hard type bucking is preferred. This has to do with the amount of “grip” they have. Hard buckings have less grip. Cold weather turns buckings harder.
-Soft type buckings also seal the hop up unit to the barrel better, for higher FPS.
-If your hop up unit backs off as you fire, tighten down the screw or put a small washer behind it.
-The bump a regular hop up nubs makes versus a H-type (illustration)
-With all hop ups it is important to periodically lube them with 100% silicon spray.
Figure 1: Testing your shim job (even though this gearbox actually doesn’t need shims)
Figure 2: Put the screw into your spring guide to help lock it in place.
Figure 2: Put the screw into your spring guide to help lock it in place.
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