CM16 Fps downgrading

[Funnyhat29]

Hey,

So a few years back I bought my first airsoft rifle, a cm16 raider, because who doesn't? I have already internally and externally upgraded it. Currently it has 363mm 6.03 tbb internally.  This put me originally on 348 fps, however since it hasn't been used as much, the fps has been seen to be nearly 360 fps, and due to laws I have obviously taken this apart and am needing to downgrade it, ideally I would like to hit 330fps as this keeps me safely under 350fps and means I can play at most cqb sites.  I am wishing to upgrade my hop-up unit to a flat hop system, this will presumably change fps, and I am going to need to change my spring and I thought I may as well do spring guide whilst I am in there.  So my question is what spring should I go for? Ideally I don't want to go over 350fps at any point, and the over time I know the spring will settle, getting under 330fps is not a must but it is a wish.  I was looking at an sp90 spring by guarder or possibly an m100 non-linear spring and maybe cutting it if need be.  Which one should I go for? considering possible fps changes due to spring guides and hop up.  I know this is a waffley post but any discussion or advice is very much appreciated

Richard

 

[Sitting Duck]

Have you already corrected AoE ?

if not that should drop you about 10-15fps

Did you fit a bearing spring guide

or is there still a spacer inside the piston ?

if so put back stock spring guide

or remove piston spacer will drop 15 to 20fps

Did you fit a new spring in there

was it a irregular spring and fitted wrong way round ?

the tighter coils should be at back of box/ spring guide

if you have the tighter coils at front of piston head

then that increases fps by 10 fps aprox

There is 3 options or ideas to drop or increase fps a smidge

no point buying a new spring that resets the guess work

there are other slight tweaks to drop say 5 fps

like spacing hop unit a fine whisker forward

so the lips just blow a tiny tiny bit and you lose a tiny bit fps

can't go nutz coz mag might not fit into hop feed tube

but it can if done just right drop fps a smidge

then as spring/seals get worn remove the thin card/rubber/o-ring

(thus boosting fps backup again)

 

[SCAR_Jester]

You can also get a ported piston or cut ports.
Do some research into volume matching, I think for the CM16 (363mm barrel), you want either a 3/4 cylinder or 4/5 one. (I believe it is unported stock)

These terms will all make sense when you look up volume matching and barrel to cylinder ratios.  

Good luck

 

[Funnyhat29]

Hi, thanks for the replies, I was thinking of doing a piston upgrade later down the line so may look at that later on in my slow upgrade process, I think I will stick with an m90 spring, as this will definitley lower fps, and if after all the other upgrades (hop up and spring guide) I find my fps is too low, I can always get another spring or cut my current one.

 

[SCAR_Jester]

Watch though, high speed builds about 18+ rps on 300+fps should be cautious of pre engagement.

 

[Sitting Duck]

Correct the AoE, stick a 3mm or 4mm thick 20mm diameter rubber washer on there

clean up head, washing up liquid to degrease

check, reglue the std thin rubber if needed

then superglue another washer on there

should use sorbothane, but a washer will do at a push

can do the silicone sealant mod for AoE too but needs 24 hrs to dry

Remove the 5mm plastic spacer and use a shorter M3 bolt with penny washer

But up to you

 

[Funnyhat29]

That was another question I had, I was thinking of making the jump to lipo, I am not too scared of wiring a mosfet into the gearbox, and I know a 7.4V lipo on stock motor should be fine, and 11.1V would probably lead to the quick death of my standard gears.  Will a 7.4V see a good increase in rps? or will it be barely noticeable, I normally play semi only though so it's the trigger response I am mainly interested in.

 

[Sitting Duck]

Solder deans connectors is a must

7.4v 20c or 25c will equate to a good 8.4v or even 9.6v

(once you upgraded to deans over small tamiya)

motor if a grey with black cap 18k std G&G is crap

if a blue or orange cap motor that is better 25k decent motor

change motor to a shs high torque or RA oem high torque

run a 7.4v will do you proud

but gets fps down, correct AoE is a wise move

motor can wait a while - not a real must tbh

see how it goes but deans if you can solder is best upgrade £ for £