GTA
All Springer/NP/PCP Air Gun Discussion General => Air Gun Gate => Topic started by: Tarheel on February 01, 2012, 03:40:42 PM
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What effect does the weight of the Piston have on performance in springer rifles ?
Would lightening the piston affect velocity negatively ?
Would it lessen or increase recoil ?
Would the effect of a lighter piston change, depending on pellet weight?
Thanks !
Dave
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Is has been said on the internet.
A heavy top hat and weeker spring can boost power of a springer with little affect on recoil. But if you add a heavier piston weight to an already powerful spring you will create much more recoil ( IE Hatsan 125).
The piston weight translates into inertia and momentum, the more inertia the more power, the more momentum the more recoil. Something like this... I am not a rocket scientist, but the guys explaning it on the web must have been.
Guys like Bob, Gene and shadow as well as other tuners probably play with this setup to tune for a specific pellet weight.
This has come from the web, while I was trying to boost power from my spring guns. You have to play with both ( spring and top hat) weights and wire size to come up with the best function.... This is the part I failed at.
Rob
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Is has been said on the internet.
A heavy top hat and weeker spring can boost power of a springer with little affect on recoil. But if you add a heavier piston weight to an already powerful spring you will create much more recoil ( IE Hatsan 125).
The piston weight translates into inertia and momentum, the more inertia the more power, the more momentum the more recoil. Something like this... I am not a rocket scientist, but the guys explaning it on the web must have been.
Guys like Bob, Gene and shadow as well as other tuners probably play with this setup to tune for a specific pellet weight.
This has come from the web, while I was trying to boost power from my spring guns. You have to play with both ( spring and top hat) weights and wire size to come up with the best function.... This is the part I failed at.
Rob
Rob,
I am curious if the piston weight should be decreased when switching to a 180 bar gas ram ?
I assume the easiest way to lighten a piston is by drilling holes in the skirt . . .
I'd like to hear more thoughts about this from anyone who would like to contribute.
Thanks !
Dave
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Drilling holes in the back side of a piston is one way to decrease weight.
This was done to my 34 .177, I believe it had been tuned for cphp 7.9 grain pellets as it was shooting them at 921 fps.
When I switched to the vortek spring (not kit) it dropped to 880 fps, as this spring was no where as long as the OEM one.
Before drilling anything I would install the gas ram then find out if it has too much recoil. Then you can try removing material one drill hole at a time to find the best setup.
Also if you go to a real heavy pellet you may want the weight of the piston to help the pellet down the bore, I would play with pellet weights first to see if one can be used with good accuracy that will also help dampen the forces being applied internally before doing something that is permanent.
Rob
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Is has been said on the internet.
A heavy top hat and weeker spring can boost power of a springer with little affect on recoil. But if you add a heavier piston weight to an already powerful spring you will create much more recoil ( IE Hatsan 125).
The piston weight translates into inertia and momentum, the more inertia the more power, the more momentum the more recoil. Something like this... I am not a rocket scientist, but the guys explaning it on the web must have been.
Guys like Bob, Gene and shadow as well as other tuners probably play with this setup to tune for a specific pellet weight.
This has come from the web, while I was trying to boost power from my spring guns. You have to play with both ( spring and top hat) weights and wire size to come up with the best function.... This is the part I failed at.
Rob
Rob,
I am curious if the piston weight should be decreased when switching to a 180 bar gas ram ?
I assume the easiest way to lighten a piston is by drilling holes in the skirt . . .
I'd like to hear more thoughts about this from anyone who would like to contribute.
Thanks !
Dave
I don't know about gas rams, but I've read that Chris from C.A.P. airguns reduces the weight of the piston in his webley patriots when tuning for power. I've read that he's also increasing the stroke length, so I'm assuming that the piston has to move faster to complete the stroke before the pellet begins to move, thus maximizing pressure in the compression tube and velocity. That may require a lighter piston. Plus, with a longer stroke, the piston might have a little more momentum. With the aded momentum, a heavier piston might do little more than just recoil harder, and maybe even slam. Imagine how many guns you'd have to sacrifice in order to find that perfect balance, playing with the length of the stroke. Then, you have to be able to repeat it.
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Imagine how many guns you'd have to sacrifice in order to find that perfect balance, playing with the length of the stroke. Then, you have to be able to repeat it.
lots, been there and done that, when I was in my crosman stage. Spent tons of money and ended up with lots of parts and back at the beginning.
Rob
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Drilling holes in the back side of a piston is one way to decrease weight.
This was done to my 34 .177, I believe it had been tuned for cphp 7.9 grain pellets as it was shooting them at 921 fps.
When I switched to the vortek spring (not kit) it dropped to 880 fps, as this spring was no where as long as the OEM one.
Before drilling anything I would install the gas ram then find out if it has too much recoil. Then you can try removing material one drill hole at a time to find the best setup.
Also if you go to a real heavy pellet you may want the weight of the piston to help the pellet down the bore, I would play with pellet weights first to see if one can be used with good accuracy that will also help dampen the forces being applied internally before doing something that is permanent.
Rob
Rob,
This is my line of thinking, too. I was just exploring my options.
Thanks !
Dave
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I just realized that I forgot to give any "particulars" about the rifle in question . . .
It will either be a Hatsan 125 or Walther Talon Magnum in .22 caliber, with a 180 bar gas ram swapped in. ( I still have a Hatsan 135 in the back of my mind if the "swept volume" is higher ).
After playing with some numbers, I believe it should be capable of producing these numbers:
14.3 gr - 1070 fps = 36.4 fpe
18.2 gr - 950 fps = 36.5 fpe
21.1 gr - 880 fps = 36.3 fpe
25.4 gr - 800 fps = 36.1 fpe
28.4 gr - 760 fps = 36.4 fpe
Dave
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Piston weight does affect performance but it is a tricky balancing act. I'm not an expert but have thought about it and done some experiments. So here are my thoughts:
The spring produces kinetic energy in the piston.The kinetic energy is used to compress the air. The piston should use up all of it's kinetic energy just as it comes to rest. At which time the pellet has moved far enough down the barrel so that the air pressure remaining against the piston is just enough to balance out the spring preload. Then you have no piston slam and no piston bounce. That is the ideal. But it is rarely perfect. Excessive piston bounce means you are not getting full power. Excessive piston slam can break things and hurt accuracy. Excessive bounce - increase the weight. Excessive slam - decrease the weight.
If you are increasing the spring energy, it is possible that you will need to increase the piston weight in order to achieve maximum power. Pellet weight may even affect the optimum piston weight
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i agree with all that has been said;i may be fortunate i did nothing to my piston other than put a maccari seal on it and polish it,and the chamber,and with the 180 bar/5k shots so far,no problems,now itpro drilled holes into his piston of the tf-87,and it was to lighten it up to increase the speed at which the piston traveled,and the piston he drilled the 1st time deformed after a while,he thought he may have taken a bit to much off,after the new piston assembly was installed i don,t know if he drilled holes again or not,his tf-87 was surely a powerhouse,and it loved the 28.4gr pellets from eunjin too.i am no sci-guy at all i would leave those things to bob and scotchmo,they seem to have that stuff down pretty good,i do know that itpro told me the talon has a lot more volume than the tf-87,and he taught me a lot,i have seen the piston on the tf-87 and it is not as thick as the one on the talon,i guess i got lucky the first time out with my talon and got that perfect setup.donno what the perfect set up really is, but i am very happy with this beast,as well as the r.a.m,both are powerful and very accurate and fun to shoot,, ;D
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i do know that itpro told me the talon has a lot more volume than the tf-87,
Speaking of "volume" . . .
Can anyone tell me if the Hatsan 135 has a great "swept volume" than the Hatsan 125 / WFH / WTM ?
Thanks,
Dave
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So how can I tell if I have excessive bounce or slap?
I am about to tune an old AA side lever and the recoil is awful.
Thanks
Jon
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i do know that itpro told me the talon has a lot more volume than the tf-87,
Speaking of "volume" . . .
Can anyone tell me if the Hatsan 135 has a great "swept volume" than the Hatsan 125 / WFH / WTM ?
Thanks,
Dave
same power platform,125/135
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So how can I tell if I have excessive bounce or slap?
I am about to tune an old AA side lever and the recoil is awful.
Thanks
Jon
The harsher the recoil, the bounce is more pronounced.
The slap would be a forward movement followed by a metalic sound of the piston bottoming out.
The AA with bad recoil could several things... bent spring, sloppy spring guides, unpolished spring ends that are biting into spring guides.
The topics above your post are usually present when fitting much more powerful spring, or reducing weight in the piston or a combination of the two.
The recoil you are feeling is more than likely worn parts or to heavy/light a pellet with worn parts. There can be much said for nice tight spring guides which will reduce twisting(torque) and recoil.
A tune will help you and some new parts... maybe a vortek kit or a vmach kit, there is also maccari kits available these will take care of your problems as long as you do a complete tune.
Rob
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I have no idea and have been wondering the same thing, but i will let you know what my test results are. I am taking a npss 22 and i am machining i think about 25 thou. out of the center of the piston because the 180 bar nitro ram that i am replacing the stock ram with was a little fatter don't have all the #s in front of me there at the shop. Currently i am waiting on the correct tool for the lathe, should have all this done and tested by next sun. also i will be testing 3 pellets 18 jsb 16 polymag and 15.9 jsb i have a crony. and will post all the #s furthermore i will be testing with a special ram scale and my press at shop to get accurate psi on std ram and n forcer ram, I will test psi at initial stroke of shaft half stroke and full stroke. i will also measure weight of std piston vs. cut weight. I was told by the engineer at kaller that on there rams psi is linear so i plan on testing gas ram location if necessary. i have already made parts to b able to preload ram in 1/8 th inch increments up to half inch. these parts will take the place of the std cup that holds the but of the ram. so not only can i vary the pressure in the ram i can also back it up so as not to use full stroke therefore decreasing cocked psi. My goal is a lofty 1 i would like to see the 18jsb at 950 fps 36 fpe i will also be looking at cocking effort,sear strength,recoil,piston slam and cocking arm strength, don't know if i was lucky or not but my npss is very accurate 5 shot ragged 1 hole at 40 yds off bags i mention this because i do not want to loose any accuracy. other mods include brass washers, stiff chisel spring,debur and polish,foam in stock and trigger. For the record i have a kaller ram and dadco ram on the way have 3 pistons and lots of seals already. cant wait weekends are for playing will let you know what i find out. Hoping to knock a crow backwards of a limb at 50 to 70 yds. ;D
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I have no idea and have been wondering the same thing, but i will let you know what my test results are. I am taking a npss 22 and i am machining i think about 25 thou. out of the center of the piston because the 180 bar nitro ram that i am replacing the stock ram with was a little fatter don't have all the #s in front of me there at the shop. Currently i am waiting on the correct tool for the lathe, should have all this done and tested by next sun. also i will be testing 3 pellets 18 jsb 16 polymag and 15.9 jsb i have a crony. and will post all the #s furthermore i will be testing with a special ram scale and my press at shop to get accurate psi on std ram and n forcer ram, I will test psi at initial stroke of shaft half stroke and full stroke. i will also measure weight of std piston vs. cut weight. I was told by the engineer at kaller that on there rams psi is linear so i plan on testing gas ram location if necessary. i have already made parts to b able to preload ram in 1/8 th inch increments up to half inch. these parts will take the place of the std cup that holds the but of the ram. so not only can i vary the pressure in the ram i can also back it up so as not to use full stroke therefore decreasing cocked psi. My goal is a lofty 1 i would like to see the 18jsb at 950 fps 36 fpe i will also be looking at cocking effort,sear strength,recoil,piston slam and cocking arm strength, don't know if i was lucky or not but my npss is very accurate 5 shot ragged 1 hole at 40 yds off bags i mention this because i do not want to loose any accuracy. other mods include brass washers, stiff chisel spring,debur and polish,foam in stock and trigger. For the record i have a kaller ram and dadco ram on the way have 3 pistons and lots of seals already. cant wait weekends are for playing will let you know what i find out. Hoping to knock a crow backwards of a limb at 50 to 70 yds. ;D
good luck with all that smokey;;sounds like you got it all planed out;;keep us posted..