CA SVD (semi only v7 GB) advice required re: spring length

[eztiger]

Hi,

I am in the process of upgrading my CA SVD to 400 fps and need some advice on how to proceed:

When i opened my gearbox i noticed that the stock CA spring was about an inch shorter than my upgrade spring (systema energy m120). I was a bit wary but decided to get the m120 into the gearbox and see what happened.

When firing with the longer Systema m120 fitted i noticed that i had to perform 2 trigger pulls before the gun would fire on the third. I imagine based on the gearbox noise and behaviour that those initial 2 cycles were needed to pull the piston back on the longer spring before it was ready to be released on the third.

Now is this behaviour down to the spring being too long for the gearbox OR is this behaviour down to my motor not being powerful enough to pull a longer spring (TM high torque fitted)?

(i have since trimmed the spring to the same size as the stock CA one and the gb is cycling correctly now but would like to fit another m120 if my cut down systema has too low fps due to cutting)


Cheers,

[sj_asc]

Re: CA SVD (semi only v7 GB) advice required re: spring length

It's normal for aftermarket springs to be a little longer, particularly those like Systema that have non linear coils.
TM's highest torque motor is their EG1000, it's not that powerful on the grand scale of things, however pulling a Systema M120 on stock ratio gears should not be an issue, it's something that has been done in the US for many years without any issues.
If you have already cut the coils, be sure to finish them is as flattest way possible to minimize the risk of them binding on compression.
I would have suggested trying to cycle it through with a straight connection from the battery to the motor, because if it had cycled it would have ruled out the motor and spring length.

It would have been worth checking that the piston could be pulled all the way to the back of the box and over the spring guide bearings (showing that it can be fully compressed).

In the case of the spring being too big (tried fitting a V4 400% in a V2), you can remove the ball bearing block in the piston head and replace it with a lower profile block freeing up some space. The piston head bearings aren't necessary if you have them on the Spring guide. Just be sure that if you do replace the piston bearings that the replacement block is still capable of partially supporting the pistons metal release tooth rack.

[eztiger]

Re: CA SVD (semi only v7 GB) advice required re: spring length

Thanks for the advice, theres some very useful tips there i'll be using in future!

I forgot to mention that the piston used in my gb is a CA 19 tooth extended piston fro the CA-25, do you think that this type of piston coupled with the full length non linier systema spring may have added to the problem?

[richardy]

Re: CA SVD (semi only v7 GB) advice required re: spring length

Id double check you have it all assembled correctly, it should be one trigger pull and away it goes. If its anothing like the CA v7 in the ebr then the shell is a toughy to get back together and maintain shimming etc without it all failing apart i just remember it being a fiddly one verses a tm v7. Also the wireing was tiny, like speaker wire from a skoda. if you trying to push that bigger spring and your wirings similar it might be worth upgrading that and your motor to a high torque jobby.

[eztiger]

Re: CA SVD (semi only v7 GB) advice required re: spring length

Thanks for pitching in richardy,

Identifiying the gearbox has been a real pain and im still not completely sure what version it is, im settling for a M14 v7 semi only gb based on my research.

I finally got to the bottom of the problem after chatting to a friend who had nothing but problems trying to get a non linier upgrade spring to work with his vfc m4. After hearing about his problems I just had a feeling that maybe i was in the same boat so i went out and bought a Madbull linier M120 to see if it would sort the problem.

And it did! :D

Now I need to work out if theres any airseal problems as it chrono'd at 378 fps but to be honest i really didnt see any noticible range increase when i used it last w/e

[richardy]

Re: CA SVD (semi only v7 GB) advice required re: spring length

hmm fun and games, the diff between non linear and linear is simply a non linears rating is based over an average, the concept being the first portion is easier to compress... then the last portion harder, colmunating in a rating equal to the similar linear spring, the idea being to take some load off the pick up tooth.

Whats more likely is the over all compressed length is not compatible with your gearbox.. id try a madbull m130 then and see where it leaves you.. none or a non consistant increase of fps might indicate an air leak. Or you could try taking a few coils off the non linear spring to help reduce its overall compressed length. removing bearing spring guides and piston heads is also another option..

truth is most guns as theres such variety nowadays, we are all pioneers, certainly the first ive heard of with a CA dragonov, so maybe the CA m14 v7 gearbox is designed for a slightly shorter spring, maybe everyone with working upgraded CA m14s would be better off going one spring bigger and shorting it slightly for a less resistive gearbox dispite the stronger spring..

makes you think dont it