Low FPS

[jdizzy]

Just a quick one guys, does anybody know the rough fps on a standard G&G Cm16 raider? I got it chronographed yesterday and it was shooting 247, now to me that's frigging low. If it is low, there's obviously a problem, compression maybe?

Any help would be great.

[Stealthkiller]

Re: Low FPS

Or the spring has been left compressed in storage ?

[Lt3033]

Re: Low FPS

I would say that is low even for a TM never mind a G&G.

Is it a new gun?

[Stealthkiller]

Re: Low FPS

New guns always lose a bit of fps once they bed in . If its a consistent fps you may have to fit a more powerfull spring to bring it back up . What did it originally chrono at ?
Could the chrono be reading wrong .?

[jdizzy]

Re: Low FPS

I would say that is low even for a TM never mind a G&G.

Is it a new gun?

It's not new, but it's not even a year old. Does have a madbull tight bore and a different hop.

New guns always lose a bit of fps once they bed in . If its a consistent fps you may have to fit a more powerfull spring to bring it back up . What did it originally chrono at ?
Could the chrono be reading wrong .?

First time I had it chronoed as it's my back up gun. So I couldn't tell you the previous fps. Well there was a few chaps that were abit shocke at their low fps on the sites chrono. So that's a possibility.

[Lee 303]

Re: Low FPS

I would expect 320ish but have found that most air leaks on the G&G Raider are due to the seals on the smaller cylinder on top of the main cylinder for the pneumatic blow-back leaking
Mainly its the O-ring on the rod but sometimes it can also the cylinder end cap seal

[Caldymoose]

Re: Low FPS

That is low, you have said the gun is not brand new, but even after bedding in the FPS wouldn't drop by nearly 100. So, my guess would be that the spring has been left in a compressed state for a long period of time, or that an O ring has failed inside and is causing an air leak.

I'm not sure how comfortable you are with taking gearboxes apart, but I would suggest opening it up and taking a look at the spring to start with. Has it been clipped previously? Does it look a bit, errr, fubared? Shorter than normal? If the spring looks in poor shape then try switching that to start with and see where that gets you. If that doesnt really help, then its probably an air leak. Take your compression components out, clean them all well, and re-apply a load of silicone grease. Pop your finger of the cylinder head/nozzle, and insert the piston. You should be able to compress the air inside a bit, but then no more. If you can push the piston in further, its a poor seal in there.

If the gearbox parts are OK, look to the hop unit. Tears in hop rubber?

[jdizzy]

Re: Low FPS

That is low, you have said the gun is not brand new, but even after bedding in the FPS wouldn't drop by nearly 100. So, my guess would be that the spring has been left in a compressed state for a long period of time, or that an O ring has failed inside and is causing an air leak.

I'm not sure how comfortable you are with taking gearboxes apart, but I would suggest opening it up and taking a look at the spring to start with. Has it been clipped previously? Does it look a bit, errr, fubared? Shorter than normal? If the spring looks in poor shape then try switching that to start with and see where that gets you. If that doesnt really help, then its probably an air leak. Take your compression components out, clean them all well, and re-apply a load of silicone grease. Pop your finger of the cylinder head/nozzle, and insert the piston. You should be able to compress the air inside a bit, but then no more. If you can push the piston in further, its a poor seal in there.

If the gearbox parts are OK, look to the hop unit. Tears in hop rubber?

When you say compressed? Do you mean not fired in a while?

I'm pretty confident, so ill whip her apart and take a look, not sure what you mean by clipped? The spring in the gearbox? Not a clue if it has.

Compression parts? Piston ect? I'll give that test ago? If that compresses? New o ring?

Where does the hop up rubber sit?

Thanks for your help

[Caldymoose]

Re: Low FPS

Well, any main spring in the gearbox will be compressed to some extent when its installed, I mean that if the piston has been held in the 'back' position (ie, the gun has half cycled, piston has been drawn back but the gears haven't cycled fully so the piston has gone back forward), which puts the spring into its most compressed state. If its been left like this for a long time, it will have an adverse effect on it.

Clipped spring, could be to reduce the FPS, instead of a new weaker spring being installed, somebody has clipped a few coils off the existing one, thus shortening it. If you clip too many off, the FPS would drop a fair amount. But, if you bought the gun new, this wont have been done, if you bought the gun 2nd hand, there is a potential it was done. Some people are lazy and don't buy a new spring!

Compression parts are: Cylinder, cylinder head, air nozzle, piston, piston head.
Cylinder head and the piston head will certainly have o rings on them, so check these first. These O rings should always be slightly oversized to create an airtight seal, but some cheaper airsoft guns will come with slightly smaller o rings, so the airseal isn't always as good. Check these for any breaks, cracks etc, then add some silicone grease to them. The air nozzle could have a small O ring on the inside of it (some higher end ones and aftermarket ones do).

The little test I described above is a good way of checking. You will be able to push the piston in part way into the cylinder until the air in there has been compressed, but it should then stop. If you can push it in a fair way, or you can keep pushing it down, its an air leak.

The hop rubber sits around the inner barrel, inside the hop unit. This is what actually makes contact with the BB through the little window on the barrel. If there is a tear in this, or its not been installed correctly, air can leak out.

[jdizzy]

Re: Low FPS

Well, any main spring in the gearbox will be compressed to some extent when its installed, I mean that if the piston has been held in the 'back' position (ie, the gun has half cycled, piston has been drawn back but the gears haven't cycled fully so the piston has gone back forward), which puts the spring into its most compressed state. If its been left like this for a long time, it will have an adverse effect on it.

Clipped spring, could be to reduce the FPS, instead of a new weaker spring being installed, somebody has clipped a few coils off the existing one, thus shortening it. If you clip too many off, the FPS would drop a fair amount. But, if you bought the gun new, this wont have been done, if you bought the gun 2nd hand, there is a potential it was done. Some people are lazy and don't buy a new spring!

Compression parts are: Cylinder, cylinder head, air nozzle, piston, piston head.
Cylinder head and the piston head will certainly have o rings on them, so check these first. These O rings should always be slightly oversized to create an airtight seal, but some cheaper airsoft guns will come with slightly smaller o rings, so the airseal isn't always as good. Check these for any breaks, cracks etc, then add some silicone grease to them. The air nozzle could have a small O ring on the inside of it (some higher end ones and aftermarket ones do).

The little test I described above is a good way of checking. You will be able to push the piston in part way into the cylinder until the air in there has been compressed, but it should then stop. If you can push it in a fair way, or you can keep pushing it down, its an air leak.

The hop rubber sits around the inner barrel, inside the hop unit. This is what actually makes contact with the BB through the little window on the barrel. If there is a tear in this, or its not been installed correctly, air can leak out.

Thanks man, you've been awesome.

If I do need a new o ring for the piston or a new hop rubber, I take it most are a standard size across all guns?

[Caldymoose]

Re: Low FPS

No worries!

Hop rubbers are NOT universal. Some guns like some Gas Blow Back rifles, snipers (VSR series) and such take different hop rubbers. The majority of AEG hop rubbers are all the same, so you shouldnt have too much issue finding the correct type. Look for either a normal TM hop rubber (usually will say for TM AEG or something like that), or the Madbull Blue/Red rubbers. Have a look, find what you like then you can always post a link back (just make sure its not to another retailer as there is nobody else (there is, just not on this forum) to Z1) on this thread and we can help.

O Rings, do yourself a favour and dont buy these from an airsoft retailer! They will royally molest your wallet if you do. I bought a set of something like 200 assorted O rings from Amazon for about £4 posted. Just to put this in perspective, another airsoft retailer wanted to charge me £1.50 PER O RING, PLUS POSTAGE!! O rings are not unique to airsoft, so any hardware shop, plumbers store, anywhere will do o rings. I cannot remember the exact size off by heart, but if you buy a selection like I did, there will almost certainly be something in there that fits. Just remember, slightly oversized for best air seal!

[jdizzy]

Re: Low FPS

No worries!

Hop rubbers are NOT universal. Some guns like some Gas Blow Back rifles, snipers (VSR series) and such take different hop rubbers. The majority of AEG hop rubbers are all the same, so you shouldnt have too much issue finding the correct type. Look for either a normal TM hop rubber (usually will say for TM AEG or something like that), or the Madbull Blue/Red rubbers. Have a look, find what you like then you can always post a link back (just make sure its not to another retailer as there is nobody else (there is, just not on this forum) to Z1) on this thread and we can help.

O Rings, do yourself a favour and dont buy these from an airsoft retailer! They will royally molest your wallet if you do. I bought a set of something like 200 assorted O rings from Amazon for about £4 posted. Just to put this in perspective, another airsoft retailer wanted to charge me £1.50 PER O RING, PLUS POSTAGE!! O rings are not unique to airsoft, so any hardware shop, plumbers store, anywhere will do o rings. I cannot remember the exact size off by heart, but if you buy a selection like I did, there will almost certainly be something in there that fits. Just remember, slightly oversized for best air seal!

Ahh right ok, we'll I've got a set of assorted o rings at my moms house so I'll take a look in there.

I've pulled the gearbox apart and did the test you said..

If I pushed the piston in slowly with my finger on the end it went al the way in.

If I pushed a little faster is had some resistance but still went to the end.

I did notice a small purposely cut out hole on the bottom of the cylinder? Is this meant to be there?

Thanks again.

[emergencychimp]

Re: Low FPS

Ahh right ok, we'll I've got a set of assorted o rings at my moms house so I'll take a look in there.

I've pulled the gearbox apart and did the test you said..

If I pushed the piston in slowly with my finger on the end it went al the way in.

If I pushed a little faster is had some resistance but still went to the end.

I did notice a small purposely cut out hole on the bottom of the cylinder? Is this meant to be there?

Thanks again.

Was your raider the blowback version?

the blowback versions have another piston system that runs ontop of the gearbox and is powered by some of the air being released from a small hole in the cylinder. If someone has removed the blowback feature and not replaced the cyclinder that is allowing a load of air escape on every shot, through that hole, instead of a small amount of air previously, this will cause your fps to be around 240-250.

http://forums.zeroin.co.uk/showthrea...-amp-g-barrell shows a pic of my cylinder which I replaced after removing my blowback system. If it's like this, it was a blowback version and this is the cause of the low fps, which needs a new cylinder to fix. Standard cylinders need a section filing away to fit as a standard one doesn't allow the gearbox to close properly.

[Caldymoose]

Re: Low FPS

If you can push the piston right down to the bottom of the cylinder with your other finger on the end of the cylinder head nozzle with very little resistance then you have an air leak. Either between the piston head and the walls of the cylinder, or around the cylinder head, or both. Try swapping the O ring on the piston head if you can, or look at buying a new piston head and/or cylinder head.

Where is the hole in the cylinder? When you took the gearbox out of the gun, was the hole towards the back of the gearbox, visible on the side? What shape if the hole too? If it what i think it is, its the port of the cylinder. Its there to match the air volume in the cylinder with the air volume of the barrel. Cylinder sizes are pretty standard for gearboxes. Long story short, the air volume in there has to match the barrel. So, the port allows some air to escape before the rest is pressurised.

If the hole is in another place or looks home made....not sure. Pics might help!

[jdizzy]

Re: Low FPS

Was your raider the blowback version?

the blowback versions have another piston system that runs ontop of the gearbox and is powered by some of the air being released from a small hole in the cylinder. If someone has removed the blowback feature and not replaced the cyclinder that is allowing a load of air escape on every shot, through that hole, instead of a small amount of air previously, this will cause your fps to be around 240-250.

http://forums.zeroin.co.uk/showthrea...-amp-g-barrell shows a pic of my cylinder which I replaced after removing my blowback system. If it's like this, it was a blowback version and this is the cause of the low fps, which needs a new cylinder to fix. Standard cylinders need a section filing away to fit as a standard one doesn't allow the gearbox to close properly.

It's not the blowback version.

If you can push the piston right down to the bottom of the cylinder with your other finger on the end of the cylinder head nozzle with very little resistance then you have an air leak. Either between the piston head and the walls of the cylinder, or around the cylinder head, or both. Try swapping the O ring on the piston head if you can, or look at buying a new piston head and/or cylinder head.

Where is the hole in the cylinder? When you took the gearbox out of the gun, was the hole towards the back of the gearbox, visible on the side? What shape if the hole too? If it what i think it is, its the port of the cylinder. Its there to match the air volume in the cylinder with the air volume of the barrel. Cylinder sizes are pretty standard for gearboxes. Long story short, the air volume in there has to match the barrel. So, the port allows some air to escape before the rest is pressurised.

If the hole is in another place or looks home made....not sure. Pics might help!

Here's the picture of the hole, indicated by the red arrow
It's not even round its a slight oblong.