GAS PISTON UPGRADE TO 180 BAR

[SMOKEY]

Hi well here are the test results of the n-forcer yellow 180 bar mf 19 x 100 nitro piston upgrade. I am left with questions that hopefully yall can help with. 1st off a little back ground this was done on a Remington npss 22cal. which with the short stroke is why you have to use the 100 mm ram the ram is very close to the std ram dimensions. i had to machine out the I.D. of the piston because the std. ram is .72 inches and the nforcer ram is .75 the std clearance between ram O.D. and piston I.D. was 14 thou. i decreased this to 10 thou to help stop the rocking action when cocking kinda like that kit that gene sells for the beji trails. then i machined the std plastic tophat that hold the ram centered in th chamber to accept the nforcer ram, also i had to machine the tophat deeper because the nforcer ram body is 10 mm longer than the std one. i took 2 mm out of the depth of the tophat so that when cocked the nforcer ram was only 1 mm from completely bottomed out. full power setting, now for the suprises stock with home tune my npss was shooting cphp at.
717.1
707.4
711.3
708.2
715.4
that was the last 5 shot string i did on 1/18/2012 gun has brass washers trigger foam in stock and off the bench ragged 1 hole groups at 40 yds with jsb 15.9. so after ram install and lube it went like this again with cphp which i use for testing cheap & available
732.2
730.9
733.5
730.0
733.5
i would think those #s would allow us to assume the lube job was good and there was no dieseling.i am leaving out the details that cocking was smooth no weird stuff going on.
here's some more details cocking lbs with bathroom scale went from 39 to 47 lbs it was a pretty hard cocking motion also with another scale and a hydraulic press i measured the starting force of the std ram so compressing the std ram and right when the shaft moves 1/16th of an inch the poundage was 185 lbs this is not pressure of charge in the ram its the amount of poundage that it took to compress the ram i had no way to measure ending force. did the same test with the nforcer ram and it moved at 220 lbs.
 The biggest suprise of all was that the shooting stroke was so much smoother than stock i mean hardly no recoil a huge difference in fact i thought something was wrong i fired it and was like aww man this thing is weak then i went to the crony.
 Why is it because piston weight i didn't measure the 2 pistons but it cant b much diffrent i didn't take that much weight out or does the nforcer ram have a slower fps shaft speed I'm confused now more pressure less fps shat speed doesn't make sense to me. so i tried the ram backwards with the ram body inside the piston oppsite from stock. thinking more weight going forward would maybe push the cushion of air through the hole harder well that was even worse and yes i had made the necessary spacers to have the ram come within 1 mm of bottoming like the 1st test again no dieseling or grinding it went like this with cphp by the way i tried jsb 15.9 and 18.1 with each test but am just posting the cphp #s there was nothing there.
711.7
702.8
714.2
710.9
705.3
well to sum it all up i was very disappointed and after spending all day testing and playing i put it back to stock and got out my r9 with vortek kit and punched paper that thing is awesome now I'm looking for a magnum springer and i think I'm going with the hatsan mod135 walnut 22.
1 more thing i did consider swept volume and that the gun may have been designed at full power already. any insight on all this would be much appreciated.i just decided that the 20fps gain with less recoil wasn't worth the stiffer cocking. 
 

[SMOKEY]

does any 1 have an idea why so much less recoil

[Tarheel]

Smokey,

Hmm . . . Your performance numbers certainly raise some questions.

I hope that other people with 180 bar-converted rifles will contribute here.

This is a modification that I am very interested in and will be watching this thread closely !

Dave

[Smackey54]

My only thought is that maybe a cylinder honing/polishing might help. What is the condition of the piston seal? Still a pretty tight fit?

[supertech77]

remember this is a remington,and it has a smaller chamber than the walther talon/hunter/125/135,so there may never be any big change,i bet if you do it to any of the hatsun/turkish 125/135 you will see a much bigger difference..

[Scotchmo]

SMOKEY,
You increased the spring energy by about 19% and got a 6% increase in FPE. Unless the gun is already way undersprung, that is about the best that you can hope for.

If you keep the original gas spring force but increase the stoke by 10%, you will see an increase in power without increasing the cocking force. Increasing the stroke by 10% gives you a 10% increase in total spring energy and it gives you a 10% increase in air volume. That will yield aproximately a 10% increase in FPE.

There are some purposely built low powered gas spring guns. But most gas spring guns are designed for maximum acceptable power. A 180 bar gas spring costs the same as a 130 bar gas spring. The manufacturers like to advertise high velocities. They are going to install the the most powerful gas spring that suits them and may even err on the side of too much power over smooth shot cycle since it is easier to sell a 1000fps gun.

The air is the transfer medium for the spring energy. You discovered first hand what happens when you try to transfer more energy through the same volume of air. The efficiency suffers and it is not worth the extra cocking effort for the small gain in velocity.

When converting from a wire spring to a gas spring, I choose the gas spring so that the maximum force is about the same or a little less than the wire spring. The average force of the gas spring can still be higher. That can result in a little extra power, the same or lower cocking force, and a smoother shot cycle. If your gun already has a gas spring, there is not much improvement to be had just by changing the spring.

As you saw, playing with the total piston weight can also affect performance. There is an optimum balance of spring energy and piston weight. I don't know how to determine the optimum except through experimentation.

[SMOKEY]

Hi and thanks for your input to smacky54 i have done a good hone job and polish and the piston seal is a stock seal it had about 100 shots on it for the test it still fits real nice and snug i would say just right it also looked fine after the test when i returned the gun to std. thanks for your intrest and willingness to help.
 Here's a little more info when turning the ram backwards i definitely got some piston slap and recoil jumped up to std. or more due to the weight i assume.
 Now i kinda feel like i hit sum magic # or spot whatever with ram power vs piston weight because this thing had no recoil it felt so detuned but yet the #s are up i wish i had more explanation of this.
 Another big mystry to me is ram shaft speed that has to play a part in power and recoil i am going to try and find out from n-forcer what the shaft speed is on there ram i will probably never know what the std.one is though
 Still more i have a kaller ram that i will be trying next weekend its yellow and same dimensions as n-forcer so hopefully that will shed sum light on the subject also.
 I feel like supertech and scotchmo and i think the limits of swept volume have been maximized pretty much from the factory so I'm not expecting to much from the kaller test, although the kaller ram has a much bigger difference in starting force and ending force, we will see next weekend!
 And just to let you know i have a nforcer and kaller 125 length coming for my new hatsan also that should be fun !
I have read that itpro has some super ram but i cant seem to get any info on it.So when i am done testing all these rams i would be happy to ship the ones i don't use to some of the guys on this website that plan on doing similar test just so we can all learn more and have fun doing it while saving a buck. thanks again and cant believe how much fun a grown man can have playing with air guns

[Scotchmo]

SMOKEY,

The Kaller and N-Forcer gas springs are about the same starting and ending force. When you measure the force of a gas spring, you don't measure when it starts to compress, you measure the force as you extend it. Gas springs are high friction devices. There is some hysteresis that you have to account for. The force to compress them is always higher than the force that they exert. In that respect, they are less efficient than a wire spring. The force to compress is probably about 10% greater than the force that they return. It will still be interesting to see how the Kaller spring compares. I have used them and they work well.

The manufacturer will not able able to give you the speed that the ram is operating at. That is a function of the gun that it is used in. Gas rams do have a recommended maximum operating speed. When used in an airgun, the gas ram far exceeds the manufacturers speed recommendations. Fortunately, airguns cycle very intermittently so there is not much heat buildup in the gas spring. The average speed in a spring gun is far less than the average speed in a progressive die.

Testing the gas springs in the Hatsan will be a more interesting experiment as the Hatsan has a wire spring when stock. I think you will have more room for improvement.

What is the stroke length and chamber inside diameter of your NPSS?

[thekid]

Do not have any experience with Gas pistons but do have experience with air guns.

Wonder if with the Nforcer Ram... you might have seen better numbers with much heavier pellets than the stock ram.

Like in a spring gun, if too heavy a pellet is used with a week spring/ram you will get negative numbers, as will you with lighter pellets with a much stronger spring/ ram.
The pellet would exit the barrel before maximum velocity is achieved.

Just a thought.
Rob 

[SMOKEY]

Thanks scotchmo for enlightening me on that i had no idea ! the stroke is 86.6 mm and diameter is 29 mm.also the info i have is that the n-forcer ram has a starting force of 200 and ending force of 260 while the kaller ram has a starting force of 202 and ending force of 360. but now after thinking about it for a bit i see what you mean its backwards starting force is when the ram is fully compressed and force builds to full extension of ram

[SMOKEY]

Thanks thekid i did consider this but the heaviest pellet i had was the 18.1 jsb and the #s dropped when shooting this pellet. ?? is it possible to have such great force that you actually blow by the seal, these types of seals look to me like they would expand equally to the pressure put on them

[supertech77]

smokey did you put a maccari seal on the piston or use stock seal?on my talon i used a mac seal because it has a bit larger o/d than stock"made a difference.if you used a mac seal and those are the fps number's ,then yep you are maxed out,as for NP speed" once you removed the amount of metal you did to get it to fit,you lightened up the piston,and it should of increased speed a little bit,but i think the Remington just don't have enough swept volume ,and any increase one one end like force,would show up on the other end,like power/harshness type deal,what i have learned from smarter air gunners than me,is all the speed/force/power you put into the chamber matters little if the swept volume is just not there,and that usually there is a price for power,either cocking effort or accuracy or recoil harshness.and once in a while you get lucky and hit just the right combination and all works perfect, i also noticed that on a really cold day there is a big difference in the fps of my talon NP,i would say 100fps,that is when a spring is more consistent.and on that cold day my ruger air magnum 177cal blew the doors off of the NP 22cal talon,so will i convert back to the spring on the talon?nope"cause even though the fps drops off  when real cold.the accuracy and smoothness of the shot cycle is still there at 25yards,only dropped 1 mil-dot vertical at 25yards on setting 12x ,and that's 1/2 inch ,so still in the kill zone.and it still blew threw a Pepsi can full of solid ice at 25yards,think that would probably penetrate most animals heads,imo 

[Scotchmo]

Thanks scotchmo for enlightening me on that i had no idea ! the stroke is 86.6 mm and diameter is 29 mm.also the info i have is that the n-forcer ram has a starting force of 200 and ending force of 260 while the kaller ram has a starting force of 202 and ending force of 360. but now after thinking about it for a bit i see what you mean its backwards starting force is when the ram is fully compressed and force builds to full extension of ram

360 does not sound right for the ending force on the 19mm x 100mm spring. Where did you get that information? My spec for the Kaller says 270.

The operating force works like this (N-Forcer example):
Apply 220 lbf. and the spring starts to compress. It takes 280 lbf. to bottom it out. As you release the spring it returns 260 lbf. and tapers off to 200 lbf. when it tops out. These numbers are approximate and can vary some.

[SMOKEY]

ok now i get it!! and im sorry but i was looking at 19 x 125 the info i got came off this website i forgot who posted it but it was a graph showing starting and ending force of a bunch of diffrent rams maybe supertech or smacky or you i cant remember.

[Tarheel]

I found a couple of charts online . . .  May be helpful



This one is in Russian, but it is decipherable. ( CLICK TO ENLARGE )



Dave

[Tarheel]

ok now i get it!! and im sorry but i was looking at 19 x 125 the info i got came off this website i forgot who posted it but it was a graph showing starting and ending force of a bunch of diffrent rams maybe supertech or smacky or you i cant remember.

N-FORCER "Mini-Forcer" SPECS

http://www.n-forcer.com/content/pdf/Mini.pdf

Dave