For those of you that airsoft, and for those of you that like to work on your own guns to some extent, you know what the hop up system is. For those that don't, it's the mechanism of the gun that puts a backspin on the BB so that it can fly farther with a flatter trajectory. If you don't know much about your gun i suggest that you kindly not attempt such "repairs" because this type of messing around with your gun without knowing what you're doing can quite easily render your gun from a state where it isn't shooting that great to one where it is entirely useless if you lose any one of these tiny, tiny parts.
Also, note that this is ONLY MEANT AS A TEMPORARY FIX. It more than likely does not work as well as the bucking and nub combos that are designed specifically for this purpose.
That being said, Here was my problem:
I bought a used Classic Army M15A4, and it was a steal at a rediculous price because the guy didn't know what was wrong with his hopup. So i picked it up and gave it a look. The problem was an easy fix if you know what to look for. The BB was always falling way way short of its mark, indicating that it had no backspin, in turn indicating that there was a problem with the rubber bucking assembly of the hop up.
I broke it down and it turns out the little nub (or nubbin) that pushes down on the bucking to create backspin was not damaged, but entirely missing. Having no new bucking and nub on hand, i started getting impatient because i wanted to USE this thing, and all its fancy upgrades. (tightbore, upgraded spring, etc...) So i started looking around for things to use as a replacement nub. And lo and behold, right on my desk sat the perfect implement.
Step 1: Tools
You will need:
Standard Airsoft Gun Disassembly Tools
Allen Key Set
Leatherman OR pliers and a good knife.
A Glue stick. (you could even use an empty carcass of a glue stick, you really don't need much. Your saliva may even work in a pinch)
Fine Tip Felt Pen
Step 2: Materials
You will need
-Your airsoft rifle
-the knowhow to disassemble (and reassemble) it
-a ballpoint BIC pen. It does not have to be empty, only slightly used.
Step 3: Disassemble Your Airsoft Gun. CAREFULLY.
Seriously. Be careful. I'm not going to go into a lot of detail because there are several different types and brands of guns in existence. What i have is a Classic Army M15A4, whose hopup is notoriously obnoxious. Some of the steps may or may not apply to your specific hop up.
Again, i'll say that if you do not know your gun inside and out do not attempt this. Do not follow my lead and instead be patient and take it into your local shop and have them replace the nub and bucking FOR you.
Back to the disassembly. Pull apart your gun (keeping your parts in order) and pull out the barrel and hopup assembly. Turn your hop up all the way DOWN (i.e. NO backspin on the BB position.) There will be a place on the uppermost gear where its teeth are not cut, to prevent the hopup from being adjusted to too extreme of a measure. The gears will not turn beyond this point. When your gears will not turn anymore, take your felt pen and mark where the teeth meet on these gears, so that you can reassemble the gears correctly. Take off the little clip (careful, this part can fly) where the barrel meets the hopup assembly, and pull the barrel out carefully, while applying mild pressure so that it will pull out the bucking, brass spacer, and o-ring with it.
Next you will want to pull off the uppermost gear (MAKE SURE TO MARK IT FIRST) and the axle pin where the hopup arm rotates, making sure to save all the little e-clips and things that you pull off. This will leave you able to pull out the part in the next step, which is where we make our modification.
This little swingarm has a mounting point for the nubbin, as shown. If this is missing the hopup will not work properly and your BBs will always fall short of your target. This is where your ballpoint pen comes into play.
Take your pen and pull out the ink tube. Grab your trusty, trusty knive and clip a short, 2-3mm piece off of the end. then reassemble your pen and put it back in your desk, keeping the little temporary nubbin handy.
Now take your glue stick and rub some on your finger. you need a super minute quantity of glue. This is just to keep the nubbin on during reassembly. Rub the glue from your finger onto the nubbin and secure in place on your swingarm.
Step 6: Reassemble Your Hop Up.
Now reverse the steps in your disassembly process, and piece your hop up back together. CAREFULLY. Be sure to align your marked gears correctly, and not to lose any of the small pieces.
Step 7: Ensure Working Order of Gears and Nubbin, Reassemble Your Gun.
Take your hop up, and crank the gears so that it is all the way turned on. Look down the barrel end, and if you can see the nubbin protruding from the top of your chamber you've succeeded!
Turn the gears all the way back so that the nubbin recedes into the hop up body, and reassemble your barrel and bucking assembly. Put everything back into your gun correctly, and go adjust your newly-working hop up!
I'll say again, this is only intended as a temporary fix. I intend to go to my semi-local shop at the end of the week and purchase a new bucking and nubbin that is actually designed for this purpose.
Thanks for reading my instructable, please comment and rate as you see fit!