Spring Downgrade Problem

[bencrundwell]

I've got a JG full metal MP5 which has been chrono'd at 390fps. I want to bring the fps down so I can use the gun legally and so bought a 1J Systema spring off zeroone. However now i've taken my gearbox apart the new spring it nearly an inch longer than the old one! Is this normal or have I bought a spring for a rifle not an AEG or something? Don't really fancy cramming it in and ruining my gearbox without checking first.

Anyone else found this?

[Bullet]

Re: Spring Downgrade Problem

Have you compared the gauge of the wire the spring has been made from?? You should find the systema spring alot easier to compress.

[julesbloke]

Re: Spring Downgrade Problem

Not sure about the Systema but I tend to put PDI 140 springs in my AEGs - they give me around 340/350 fps. They are about an inch shorter than most of the other springs I've tried to achieve the same fps - making them much easier to install It must be something to do with the metal as Bullet mentions above!

[ThatblokewiththeScar.]

Re: Spring Downgrade Problem

I dont have one in front of me but if memory serves the JG has the same piston set up as the TM. Inside the piston there is a small metal shock block that the spring holds onto. This will account for about 1/2" of length. Ideally you should remove this block as well or you may find the new spring will be compressed more than is intended and raise the power slightly.

Many equally rated springs have different lengths due to wire gauge being linear or non linear and number of windings. Checking the gauge of steal is OK but unless you know the tensile properties of the wire how will you know if it's Hi or Low yield?

If you got it from Z1 then it is probably correct. The only other type of spring it could be is for a Bolt action and these are typically much longer and thinner in their cross section and probably wont fit the spring guide.

You may have to perform a little surgery to remove the metal block from the piston assembly as the piston head will not always unscrew from the piston when you want it to. You will find that the piston head if it is the direct TM clone has a small disk in the center of the piston this must be cut out to access the screw that connects to the block. This must be replaced with a machine screw, washer and nut to hold the piston head to the piston without the metal block. If you have a later version with the rarer vented head just unscrew as you would any other piston head. If you get into difficulty drop me a line.

Phil...