The gen4 is a great marker but there are some manufacturing flaws that lead to the marker not working properly. I?m going to try and discuss these here and various ways to fix them and get your gen4 working flawlessly. Low Velocity Issue or Maker Not Recocking and ?Farting?
To fix a low velocity problem with the gen4 could be a number of things, but first make sure you have a full tank of air or CO2 and your marker is well oiled.
1.) Small nub between ball detents:
The most common reason for low velocity with the gen4 is the bolt sticking and not cycling smoothly. The first cause of this is a small notch inside the front of the gun on the top between the detents. This notch is from the hole for the front screw that holds the top rail on. If you have this nub of metal there just sand it off carefully until it is smooth and the bolt can move smoothly through the tube in the front of the gun without catching.
If the bolt still doesn?t move smoothly you may have to sand the notches on the side of the bolt a little deeper to help the bolt pass the ball detents easier. (Note: I used a dremmel tool to do this)
2.) Bolt sticking inside the barrel:
Also to cause the bolt to not cycle smoothly is the bolt on the gen 4 travels into the barrel a little ways. Usually aftermarket barrels are a little smaller bore so the bolt will stick inside of it and jam. You could fix this one of the following ways:
a.) Sand the start of the inside of the barrel wider so that the bolt can pass into the barrel smoothly. After you sand the small section of the inside of the barrel I would suggest polishing it with some metal polish to make it smooth. (Note: I used a dremmel tool to do this)
b.) Place a couple o-rings on the end of the threads of the barrel so that it will space it farther from the gun so that the bolt will not travel into the barrel. (Note: this will cause a gap between the barrel and the breach which could cause ball chops or inaccuracy.)
c.) You could also sand the outer diameter of the front of the bolt so that it will fit into smaller barrel bores if you did not want to sand the barrel itself as mentioned in section a. However, I would not suggest doing this to the bolt since it could cause air to escape behind the bolt and could cause the more friction for bolt operation.
3.) Check Hammer and Bolt O-rings:
A common cause for ?jackhammering? or ?farting? is one of the o-rings on the bolt or hammer are damaged or broken. Check all the o-rings the gun for tears and replace them with new o-rings. If the o-ring on the hammer has a tear or is damaged air pressure will leak behind it and not recock the gun.
4.) Get a Harder Drive Spring:
Install a harder drive spring and/or stack the drive spring with anther smaller spring. You can buy a spring kit from RAP4 or use other spyder spring kits. Use a heavier spring than the stock one and/or stack the spring with another spring towards the back on the white spring guide. You can cut the stock spring to almost the size of the spring guide and then add to the front of it a hard drive spring and this should jump your velocity up. This causes the hammer to press and hold the valve open longer and harder to allow more airflow.
5.) Get a lighter Valve Spring:
You can also make the valve easier to hold open and allow more air flow if you replace the stock valve spring in the front section of the gun with a lighter spring. You can get these springs in a spring kit, the same kits that have the drive spring have valve springs as well, they are the shorter cone shaped springs.
6.) Drill the bolts air hole wider:
If you?ve done the above steps and you still have low velocity you could widen the hole in the side of the bolt bigger to allow more airflow. Just make sure you stay between the 2 o-rings on the bolt.
7.) Drill more holes in the valve:
If you still have problems with velocity after steps 1-6 then you could take a more extreme route and drill a few extra holes in the valve. The stock valve has 2 holes currently in the middle section. You can add 2 more holes on either side of the valve to allow more airflow. Drill these holes inside of the valve in-between the o-rings as the picture shows.
8.) Sand down the valve pin:
This goes along with drilling more holes in the valve and is suggested against if you are mechanically challenged or not very steady handed. You can also increase airflow my sanding down the valve pin so that the diameter of the pin is smaller than the stock one. Just sand down the middle of the pin NOT the plastic part or the tick end. Be careful not to damage the plastic part on the end of the pin because this is what seals the valve and if it is damaged your gun will leak air.