Reducing fps slightly

[ghostwalker]

So yesterday saw the second chance to use my much maligned g&g predator.

On its previous adventure I was fairly sure it was shooting low on fps as it seemed to lack the punch of my other aegs (not range etc, just the punchyness).

So you can imagine my surprise when I stepped up to the chrome and it shot 356,357,357,357 and 357, was declared hot and put back into my gun bag(fortunately I still had my l86 as a back up).

Whilst at the chrono I was advised to trim a coil off the spring to bring it under limits. But frankly I have no idea how to do this and any advice would me greatly appreciated.

The gun is relatively new so I don't know if there's anything else I can do to lose this few fps.

Details as follows

G&g gc16 predator (full metal). No upgrades.

9.6v 1600mah Nimh battery

Using .20bb's

Has shot maybe 1500 bb's since purchase, but this was its first time across the chrono.

 

[Sitting Duck]

First off you are just over - 2% over

Secondly what about first time or not chrono'd first time out ???

(is site chrono 101% accurate or a little out - weak batteries can throw readings out but then all guns would be out too I guess)

Also fps "usually" will go down rather than up, admit warmer weather can affect the bucking a bit

but in general springs fade, seals wear etc.......

Two suggestions come to mind:

Easiest is to start using 0.25's - not to cheat the chrono

but adjust the hop a whisker more for 0.25's then chrono on 0.20's should show readings under 350fps

This is "generally allowed" and use .25's anyway for better performance

(on average 0.25's will probably show around 310fps using .25's at chrono - but you inform site you got .25's or use .20's to chrono at say 347fps)

another method is to place a few bits of tape between box & hop unit to lighten the seal a hairline so you create a tiny tiny leak that will drop fps

(later on as stuff wears and fps drops in say 6 months - remove tape to improve the seal and get a little fps back)

Or place gun on full auto - ahh bugger you got ETU

Ok that idea out the window - the idea was to fire gun leaving it pre-cocked say at 90% retraction to effectively break the spring in a bit

but alas the ETU will bloody complete the cycle all the time me thinks - so it would be tricky to pre-cock it

(suppose you could pull the tamiya off but probably not wise to kill power while ETU is doing its stuff)

Think the other options are perhaps the easiest to do

reckon get some .25's dial a smidge more lift/hop and when you next just use .20's to chrono it should be below the 350 mark

use .25's anyway but chronoing with hop set for .25's is usually accepted as not directly cheating the chrono

just the hop is set with the weights you will be using

obviously if you was shooting say 375fps then yes a mod or downgrade would be needed

but 5-7 fps just over is really not going to be worth any downgrade/tweaks tbh

some sites give a small margin or a little discretion for these moments when guns are just just shooting a tiny bit over

but yeah a bit of a pi$$er if gun is just just over and site says nope

think many of us have been there - but the site goes by their chrono - even if not 101% accurate and also their rulings

think you could just scrape under without really cheating chrono - not wise to attempt this btw

but hop set for .25's should scrape under

or hairline shim forward of the hop would probably do it without needing to open her all up for 2% over

 

[ghostwalker]

Cheers sitting duck.

On the first visit to the site, my gun wasn't chronoed, so I had no real guide as to what it was firing.

But on this visit they were being super strict. It may have been as it was more of an 'open' day wth a lot of rentals, as opposed to my last visit where it was a milsim.

I figured the gun would settle a little with time and wearing in.

I use .25's as standard as I find them a little better for accuracy and range over .20's

The guy at the chrono advised cutting a coil out of the Spring, but I'm a little remiss to try that as its not exactly a reversable mod. Someone else suggested fitting a silencer to give a little more distance before the bb reaches the chrono.

Yeah the gc predator is fitted as standard with a ETU and MOSFET, so trying to keep the spring compressed is a little harder to achieve without taking the gun apart.

 

[Sacarathe]

The guy at the chrono advised cutting a coil out of the Spring, but I'm a little remiss to try that as its not exactly a reversable mod. Someone else suggested fitting a silencer to give a little more distance before the bb reaches the chrono.

Someone also suggested that to me once, but really it actually does nothing but allow you to use a hot gun. It's a tricky one. Have you also tried increasing the hop until 0.20g is at the right fps and then keep increasing the BB weight - up to 0.33g(23,25,28,30,32,33) to find the one which flies true. It may be that non of them do if the hop is insufficient. But its something you can do without opening the gearbox.

 

[Josh95]

trim the spring or buy a different one rated below 350 fps, if you're using a tight bore barrel that can increase fps

 

[ak2m4]

There's one more thing that may work. It you or a mate has a spare suppressor try fitting that. You may find that the extra 20cm is just enough so that the BB reading velocity is reduced. Never tried this myself so could be a load of old tosh...

 

[ghostwalker]

The gun is stock aside from a sight and grip being added.

I have a couple of suppressor I could try, if I can figure out how to get the one that's in there off. Seems to be a stupid split pin through a metal flash hider...grrr

Spring inside is stock which apparently should only give 335fps according to zero one lol.

 

[ak2m4]

Those split pins were designed by the devil himself I'm sure - may he burn in hell Springs can be over-rated. A M100 in theory is 335FPS max but who knows what Z1 put in there. You could just have super compression in your GB which is great, then you can downgrade the spring to a M90. If you need a Supershooter one I've got a bunch of them but it's a ballache opening up the gearbox if you don't have to.

 

[jcheeseright]

Drill a little hole through your cylinder about halfway down, start with 1mm and increase the bore til you hit the desired FPS.

Once you've done it make sure there are no burrs on the inside though or you'll destroy your piston head o ring.

 

[Samurai]

You will need an about 1.5-2 feet long suppressor.

http://mackila.com/airsoft/atp/07-a-02.htm

 

[ak2m4]

You will need an about 1.5-2 feet long suppressor.

http://mackila.com/airsoft/atp/07-a-02.htm

Sorted

 

[ghostwalker]

Despite the videos all screaming it's a split pin...it isn't. It's just a Allen key bolt with a fitting the size of an ants tadger....luckily I found an ant.....well an Allen key small enough.

I now feel a bit dirty as this doesn't feel right. Silencer on a a gun with a wire cutter style keymod rail.

Aside from the 'will it,won't it' drop the fps, I'm not sure it looks right. Yeah I'm a gun tart

View attachment 19736

 

[ak2m4]

Yeah it looks fugly indeed....You don't have a chrono do you?

 

[Sacarathe]

There's one more thing that may work. It you or a mate has a spare suppressor try fitting that. You may find that the extra 20cm is just enough so that the BB reading velocity is reduced. Never tried this myself so could be a load of old tosh...

It does work. But from a health and safety standpoint it is immoral. Though from an "is it legal(within rules not law)" standpoint it is not unacceptable or deserving condemnation.

I guess you could still get undervoluming if the suppressor is narrow enough internally.

 

[ghostwalker]

Well I want to stay within the rules as I don't want to shoot anyone with a hot gun and don't want to get shot with one.

That and there's the fact that the predator with a suppressor just looks ugly.

So that will be coming back off on both grounds.

But at least I can now order a decent muzzle break for it.

I guess initially all I can do is run rounds through it in the hope of bedding the spring in and taking off those few fps.

Gun techs aren't so easy to find here in Norfolk so I'm limited to options regarding a spring change. Doing it on a ics l85/86 is easy now I know how, but in one of these fun dangled m4's where you have to remove stock tubes, motors and all other techs bits....not so confident.

 

[Sitting Duck]

I'd avoid doing ANY internal work just for a few fps atm

It will drop in due due course

If you can source say a 8mm x 0.5mm or 1mm thick o-ring

stretch that over hop unit into gearbox it will push the hop a whisker away to slightly lessen the seal

The G&G hop unit - where it fits inside the gearbox is 11.3mm outer diameter aprox

So I would certainly consider:

http://www.ebay.co.uk/itm/Steel-Shim-Washers-Multi-Choice-3-5-6-8-10-12-16-19mm-x-0-3mm-Depth-/261824410376?var=&hash=item3cf5f37308:m:mkM7Z57Q_nyBdmHiDHhOA_w

grab a pack of 12mm x 18mm 0.3mm thick shims

place one between hop & gearbox - might need to file a tiny bit but think the outer 18mm would be ok and not foul anything

viola - hop is now pushed a whisker forward to lessen the seal and should drop fps

(probably also improve feeding a smidge too as nozzle or hop is now retracting a whisker further back to allow bb's to chamber a tiny bit better)

No Tech - no ripping box apart - a few quid and no permanent f*ck up made

6 months later as fps drops a smidge - then remove the shim and you should get some extra fps back

Loads of ways to do this sort of thing but I really would look at trying that myself with a wafer thin shim or something

Up to you though but opening her up you can do later when she needs it or something busts

Yeah you could simply correct AoE that will drop say 10 to 15fps which would normally be first thing I'd do

but if you ain't sure then leave box alone for now is what I'd recommend

 

[RR01]

grab a pack of 12mm x 18mm 0.3mm thick shimsplace one between hop & gearbox - might need to file a tiny bit but think the outer 18mm would be ok and not foul anything

viola - hop is now pushed a whisker forward to lessen the seal and should drop fps

(probably also improve feeding a smidge too as nozzle or hop is now retracting a whisker further back to allow bb's to chamber a tiny bit better)

Problem here is that pushing the hop forward slightly "could" mean the feed hole in the top of the mag is no longer in direct line with the feed tube in the hop unit and might cause feed problems for the BBs.

 

[Sitting Duck]

Problem here is that pushing the hop forward slightly "could" mean the feed hole in the top of the mag is no longer in direct line with the feed tube in the hop unit and might cause feed problems for the BBs.

If we was talking about 1.3mm yeah maybe but 0.3mm

plus the M4 hop is sprung loaded to push back, plus often there is the ol' M4 mag wobble of play

I said about a few layers of tape - couldn't find 0.1mm or 0.2mm shims in that size so 0.3mm might be his nearest option available

Other options will require a bit of modding - most would be permanent and with risk of balls up

OP "could" file the nozzle or even cut a slight nick or line in tip of nozzle to create a slight leak when sealed

But like I said these are permanent if a balls up takes place

This shimming of hop a whisker forward is a temporary idea to try, will not invoke warranty

pop the pin, slip the receiver forward, slip a shim on the hop

(could use a bit of double sided tape to affix it better but no doubt will alter the shim a touch thicker)

carefully refit the receiver back - if no tape or glue the suggest reassemble the gun downwards facing so shim stays on hop unit

What has OP got to lose ????

can be easily removed if problems arise (doubt it myself but I have been wrong)

or removed when the fps drops a bit due to wear or running in the spring etc....

£3 for 6 shims, a 50p idea to try - heck if it don't work I'll buy them off the OP so he is not out of pocket

 

[ghostwalker]

Well I have a mountain of orings etc upstairs, so I can give that a try.

 

[Sitting Duck]

Well I have a mountain of orings etc upstairs, so I can give that a try.

Result - I'm £3 richer then, but wtf I might buy some anyway as most o-rings I got to hand are quite thick

you want a really thin mofo to just push that hop a tiny whisker forward

Funny thing is - G&G don't always fit the spring at the front of the hop

much like they don't always use hex screws on gearboxes - they still use cross head screws now & then

(also in some rare cases/models can have bearings instead of 95% bronzey bushings)

In your case I reckon it may have a hop spring pushing hop back to seal nicely - too nicely

can't remember if the FFR had the spring on the hop unit - that was over the Mall's 330-340 limit first outing

I'm quite sure with a bit of experimenting you can just scrape her under by pushing the hop a whisker forward

best of luck sir