Need a little help with diagnosing an issue

[binicb2r]

I have a Dboys full metal M4 with an M120 spring. The factory spring died quite quickly and needed to be replaced and the M120 was free to me. The hopup is the factory plastic one as the metal hopups Ive tried cause feeding issues. Compression is perfect. The piston can be held back by placing a finger over the nozzle in the cylinder head and dropping the piston.

My issue is now that Ive solved all the rest of the issues on the gun and actually had a chance to chrono it I find Im shooting 267 + or - 1FPS. Consistency is there but I feel that is much too low for an M120 spring even with .23 BBs. The range is also terrible. For long shots I just go to my side arm.

I am unsure of how to continue diagnosing and finding where air might be leaking out.

[Jester316]

Probably the seal between your hop bucking and barrel.

[Toonvater]

I'm wondering what do you mean "the factory spring died quickly"?

[binicb2r]

Probably the seal between your hop bucking and barrel.

I was thinking more of the plastic nozzle but Im unsure how to test either of those.

I'm wondering what do you mean "the factory spring died quickly"?

It completely collapsed. I know some one will be thinking "stupid n00b" and tell me to release the spring tension but that was always done with all of my electric for years. Besides, that doesnt release 100% of the tension, just some of it. The less continuous strain the better though.

The spring is now the exact length of the area between the rear of the gearbox and where it sits in the piston. Im assuming sub par materials in the spring. It died in less then 4 months with moderate use.

[Mindspeed]

+1 bucking. I would start there. Easiest and cheapest thing to check.
Then maybe piston head and nozzle? O ring on piston head could need replaced.....

[Jester316]

Probably the seal between your hop bucking and barrel.

I was thinking more of the plastic nozzle but Im unsure how to test either of those.

place finger over barrel and fire. Try to keep as much air in as possible. When you remove your finger there should be an audible sound of air escaping that was being held in by your finger.

I'm wondering what do you mean "the factory spring died quickly"?

It completely collapsed. I know some one will be thinking "stupid n00b" and tell me to release the spring tension but that was always done with all of my electric for years. Besides, that doesnt release 100% of the tension, just some of it. The less continuous strain the better though.

The spring is now the exact length of the area between the rear of the gearbox and where it sits in the piston. Im assuming sub par materials in the spring. It died in less then 4 months with moderate use.

[spazzticsmurff]

I have a Dboys full metal M4 with an M120 spring. The factory spring died quite quickly and needed to be replaced and the M120 was free to me. The hopup is the factory plastic one as the metal hopups Ive tried cause feeding issues. Compression is perfect. The piston can be held back by placing a finger over the nozzle in the cylinder head and dropping the piston.

My issue is now that Ive solved all the rest of the issues on the gun and actually had a chance to chrono it I find Im shooting 267 + or - 1FPS. Consistency is there but I feel that is much too low for an M120 spring even with .23 BBs. The range is also terrible. For long shots I just go to my side arm.

I am unsure of how to continue diagnosing and finding where air might be leaking out.

you need to be putting pressure on the piston to properly test piston seal not just letting the weight of the piston hold it up and call it good. but it sounds like your compression is good. how hard was the spring to put in the gun? if it was pretty easy i bet its not realy a m120. an m120 while not overly dificult will not just pop in easy. i dont think you have a seal issue weather it be from the piston/nozzel or bucking there is usualy more variation in your fps.
one way to test if your nozzel to bucking seal is good: flip the gun upside down (mag out), put a piece of t.p. over the hop-up hole, fire the gun. if the tp flys away from the hole you have a leak between the nozzel and bucking.

im betting the spring isnt what you think it is though. doesnt matter what package it was in.

[Jester316]

I have a Dboys full metal M4 with an M120 spring. The factory spring died quite quickly and needed to be replaced and the M120 was free to me. The hopup is the factory plastic one as the metal hopups Ive tried cause feeding issues. Compression is perfect. The piston can be held back by placing a finger over the nozzle in the cylinder head and dropping the piston.

My issue is now that Ive solved all the rest of the issues on the gun and actually had a chance to chrono it I find Im shooting 267 + or - 1FPS. Consistency is there but I feel that is much too low for an M120 spring even with .23 BBs. The range is also terrible. For long shots I just go to my side arm.

I am unsure of how to continue diagnosing and finding where air might be leaking out.

you need to be putting pressure on the piston to properly test piston seal not just letting the weight of the piston hold it up and call it good. but it sounds like your compression is good. how hard was the spring to put in the gun? if it was pretty easy i bet its not realy a m120. an m120 while not overly dificult will not just pop in easy. i dont think you have a seal issue weather it be from the piston/nozzel or bucking there is usualy more variation in your fps.
one way to test if your nozzel to bucking seal is good: flip the gun upside down (mag out), put a piece of t.p. over the hop-up hole, fire the gun. if the tp flys away from the hole you have a leak between the nozzel and bucking.

im betting the spring isnt what you think it is though. doesnt matter what package it was in.

Also this. If the spring is equal in length as the distance from the spring guide to piston heard bearing, than it is not an m120. Did it start out longer and compress that much? I left my Mp5 spring compressed for 3 weeks and it only dropped the FPS by 10. And that was on a crappy JG Mp5. Best thing you can do, is buy an actual M120 spring from a reputable retailer in a brand that is trusted and go from there.

[binicb2r]

I have a Dboys full metal M4 with an M120 spring. The factory spring died quite quickly and needed to be replaced and the M120 was free to me. The hopup is the factory plastic one as the metal hopups Ive tried cause feeding issues. Compression is perfect. The piston can be held back by placing a finger over the nozzle in the cylinder head and dropping the piston.

My issue is now that Ive solved all the rest of the issues on the gun and actually had a chance to chrono it I find Im shooting 267 + or - 1FPS. Consistency is there but I feel that is much too low for an M120 spring even with .23 BBs. The range is also terrible. For long shots I just go to my side arm.

I am unsure of how to continue diagnosing and finding where air might be leaking out.

you need to be putting pressure on the piston to properly test piston seal not just letting the weight of the piston hold it up and call it good. but it sounds like your compression is good. how hard was the spring to put in the gun? if it was pretty easy i bet its not realy a m120. an m120 while not overly dificult will not just pop in easy. i dont think you have a seal issue weather it be from the piston/nozzel or bucking there is usualy more variation in your fps.
one way to test if your nozzel to bucking seal is good: flip the gun upside down (mag out), put a piece of t.p. over the hop-up hole, fire the gun. if the tp flys away from the hole you have a leak between the nozzel and bucking.

im betting the spring isnt what you think it is though. doesnt matter what package it was in.

The factory spring kinda just fell out. I grabbed the M120 off of a buddy since it was too much for his motor on nimh. And not it wasn't too bad to get in there with a guide rod to hold it in place. Without one it would have been hell. I'd have to ask him what brand. I forget.

I did the paper over the feed area and the paper did move slightly then fall off. It poped up a little.

[spazzticsmurff]

I have a Dboys full metal M4 with an M120 spring. The factory spring died quite quickly and needed to be replaced and the M120 was free to me. The hopup is the factory plastic one as the metal hopups Ive tried cause feeding issues. Compression is perfect. The piston can be held back by placing a finger over the nozzle in the cylinder head and dropping the piston.

My issue is now that Ive solved all the rest of the issues on the gun and actually had a chance to chrono it I find Im shooting 267 + or - 1FPS. Consistency is there but I feel that is much too low for an M120 spring even with .23 BBs. The range is also terrible. For long shots I just go to my side arm.

I am unsure of how to continue diagnosing and finding where air might be leaking out.

you need to be putting pressure on the piston to properly test piston seal not just letting the weight of the piston hold it up and call it good. but it sounds like your compression is good. how hard was the spring to put in the gun? if it was pretty easy i bet its not realy a m120. an m120 while not overly dificult will not just pop in easy. i dont think you have a seal issue weather it be from the piston/nozzel or bucking there is usualy more variation in your fps.
one way to test if your nozzel to bucking seal is good: flip the gun upside down (mag out), put a piece of t.p. over the hop-up hole, fire the gun. if the tp flys away from the hole you have a leak between the nozzel and bucking.

im betting the spring isnt what you think it is though. doesnt matter what package it was in.

The factory spring kinda just fell out. I grabbed the M120 off of a buddy since it was too much for his motor on nimh. And not it wasn't too bad to get in there with a guide rod to hold it in place. Without one it would have been hell. I'd have to ask him what brand. I forget.

I did the paper over the feed area and the paper did move slightly then fall off. It poped up a little.

im willing to bet that you dont have much if any leak between the nozzel and bucking then. think about how light tp or any other piece of paper/tinfoil you would have used to test this weighs compared to how much and how fast the air is moving through the barrel. if you were leaking even 10% of the air moving through the barrel the paper you used wouldnt just pop a lil, it would fly away from the hole. what moved the paper was most likely vibration from firing or the lil bit of air that the nozzel moving pushed while it moved back and forth.
what kind of cylinder is in the gun? where is the port hole. that will also affect your fps.