GTA
All Springer/NP/PCP Air Gun Discussion General => Air Gun Gate => Topic started by: cherokee on September 11, 2014, 05:35:13 PM
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Is there a way to determine spring health without taking the gun apart?
Part two to the question, if the spring does LOOK ok is there any way to really tell if it is still up to snuff, is there a device like a valve spring compressor for airgun springs?
I have an older Gamo 440, and it just does not seem to shoot like it once did. It is really all over the place with pellets it has liked before, and it seems to have a great deal more "twang" after shooting. The cocking effort seems about the same, but it is hard for me to tell as I have some medical issues that weaken my upper body strength.....so really the question comes from the grouping and the louder "twang". I also have an EXPO 26 and it does not have the noise....both guns are about the same vintage.
I have never had the guns apart and truth be known I am a little afraid of them, partly because I don't want to mess them up, partly because I don't know what I am doing and don't want to hurt myself with a spring under load. Is there any load on the spring if it has not been cocked. I have read about having to have a spring compressor, I do not have this bit of kit so I am not sure if there is any point in taking it apart.
I do all the work on my own firearms and no worries there, I also know the correct end of a screw driver....so I am not worried about the taking it apart, it is damaging the rifle, or not having what I need to put it back together.
Can anyone give me some advice.
Thanks.
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Sometimes the spring breaks and can't be detected visually without opening it up. A Chrony can help to see a drop in power or high fluctuations in fps.
There is always pre-load on a spring. The amount differs from model to model.
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Shoot that thing! If it's up to snuff, it should chrony with the best of 'em. I mean comparing to what others get out of the gun, same brand/model. Compare performance with new and old, should tell you the spring health. If it's not you to snuff, you'll need a rebuild anyway. Replace spring/piston seal. ;)
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Sounds like a Crony is a tool that is very useful in checking the overall health of these guns. I have one for when I was hand loading, but always thought that using it with airguns was for those that was much more serious about this then I am. Don't get me wrong I am having the time of my life and don't miss my firearms one bit (those medical issues I talked about before make me very recoil sensitive) Looks like I will have to dig it out and put it to work.
Can anyone point me in a direction to look up specs on what FPS this thing should be shooting at with (X) grain pellet. I have quite a large sample up to about 16g.....or could you tell my what you are getting out of your Gamo 440 hunter using what weight pellet.
If that question is better asked in the Gamo sub forum just let me know.
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Greg,
A 440 should shoot a 7.9 gr (Crosman Premier Hollow Points aka CPHP) pellet at ~ 900fps brand new after a few thousand shots may be down around 850. If you are getting much lower than that you have an issue. The issue may not be your spring though, it could be you piston seal or your breach seal. Breach seal is easiest to check with a piece of toilet tissue draped over the breach when shooting the tissue should not move or have holes in it. Next easiest to check is a visual on the spring it's self, pull the action out of the stock and look into the cocking slot, the spring should be nice and evenly spaced all along the slot if you see doubled coils it is broken. The Piston seal inspection require disassembly...
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Thank you for that, I will check it this weekend, and dig out my old chronograph, I will report back with the results.
Greg,
A 440 should shoot a 7.9 gr (Crosman Premier Hollow Points aka CPHP) pellet at ~ 900fps brand new after a few thousand shots may be down around 850. If you are getting much lower than that you have an issue. The issue may not be your spring though, it could be you piston seal or your breach seal. Breach seal is easiest to check with a piece of toilet tissue draped over the breach when shooting the tissue should not move or have holes in it. Next easiest to check is a visual on the spring it's self, pull the action out of the stock and look into the cocking slot, the spring should be nice and evenly spaced all along the slot if you see doubled coils it is broken. The Piston seal inspection require disassembly...