Lightening the ram/piston?

[aidave]

I know there's a lot of theory about a lot of things in life -- with fire arms it's reducing mass to lessen lockup time.  With motorcycles, it's about lightening the rotating mass.

Since I have the rifle torn down; I was polishing the ram (not the gas spring, but the ram with the seal on it).  It dawned on me that if it was lightened up, either by drilling or machining, as long as it was done evenly; that this would allow the gas spring to expand faster.  Day dreaming more; I thought about taking measurements and having my local machinist or one of the online prototype builders do one in T3 aluminum.

Has any one tried this? if so, did it improve anything?
 

[shorty]

 I decreased the weight of the piston in search on higher fps. Well, I didn't get any more fps. The fps stayed the same. What it did was reduce the recoil.
I used a cut off wheel on an air grinder. That piston metal is pretty "dang" hard. A drill bit ain't gonna do it.

work was done on trail np .22.

Iam still running in the 800's (fps) with RWS hobby wad cutters 12 grain and 680 to 690 fps with H and N barracuda hunter extreme HP 19.09 grain.

[Privateer]

I don't think you would get anything better from lighenting as far as a better FPS.
A Piston or spring only does one stroke. So it's the swept volume that produces power.
And that's from a dead stop to dead stop for the most part.
In an enternal combustion engine you have multi strokes at VERY high rates and the lighter the load on things like bearings and rods help produce the extra power.
Mostly from reduced friction and the rotation force being reduced on the offset pistons in such a design.
Remember, we need to move all that dead weight once the piston is done doing it's job in that application.
You may get a better acceleration at firing time with lighter parts but it is probably so small as to make the effort not worth the time as the stroke is so small.

That's just my opinion and hope to see the real experts give us the scoop.
 

[Laser-Fist]

First post here, I actually joined to research this exact question. Does removing a small amount of weight from a Nitro ram gun's piston skirt improve performance and how? My plan is to machine material out of my xl1100's piston skirt, but it still needs to be stable enough to not deform. I am looking to mostly smooth out the overall firing sequence/reduce recoil without loosing velocity. If I gain velocity great, time for a heavier pellet. Thanks guys, I am really enjoying the forum thus far. -Craig

[Privateer]

Hi Craig,

I hope the experts join in soon. (I'm new myself)
But I have a background in High output engines.
Given you have a single stroke with a limited pressure behind it?
I doubt you would gain much from chopping weight from the piston and moving parts.
I'd tend to think reduceing any friction would gain you more power.
That may involve buttoning the piston (Old Drag racer trick) to doing a total re-bore-hone depending on how tight you want to get.
I still doubt that is worth the effort for the hobby shooter.

Now if you have a semi-auto or full auto? That may be a different thing.
I know on full auto it is something to consider depending on the Gun.

I look at it this way.
IF a lighter piston made any real world difference? There would be a gazillion people out there selling them to you!
Find me one with the data to prove it.
 

[Paul68]

You wont gain any increases in either FPS or FPE. Lightening the piston is usually done to reduce recoil. Since it also reduces the mass of the piston, it reduces the momentum as well. Would you rather get hit by a golf ball going 50 mph, or a ping pong ball going 50 mph? Same thing. The lighter weight of the piston reduces its ability to overcome the pressure of the air compressed in the cylinder, so usually if you lighten the piston, you will also need to go to a slightly lighter pellet to maintain velocity and hopefully FPE. Typically though, you lose FPE regardless.

This is less a problem with gas piston rifles though because they do not work in the same manner as a spring and maintain a higher force through their full stroke rather than a gradual decrease in force as they extend as happens with a spring. It is still basic physics though, so it still applies.

[OleTomCat]

Most people add weight to the piston to gain energy from the shot cycle, this increases the felt recoil since you are moving more weight over a distance you are doing more work this work is then transfered to the air being compressed which is then transfered to the pellet, the pellet has to be tight enough not to move until most of the energy is transfered yet be out of the barrel before you start to get deminishing returns, lots of math in there but yes the mass of the piston affects both the power and shot cycle of the gun....

[shorty]

I couldn't agree with Paul 68 anymore than what he said. He commented to me about this whole fps/fpe increase idea I had a  few months ago. Unless your ready to buy new parts that you screwed up, don't do it.

Fortunately for me, I did some things to my trail thinking it would do something I wanted it to do (increase fps) and what it really did was reduce the recoil. No loss in fps yet no gain. Unless someone else can tell me their standard trail np (not xl) is pushing 12 grain pellets at 820fps and h and N ftt's pushing 750fps. Heck, the barracudas 19.09 grain are hitting 20.18 fpe.

I also should have listened to Paul68 and the rest of the guys about the transfer port hole size too. Stock is .125" and I opened it to .14". I definitely lost fps there (approximately 1.7% on light pellets but leaned out with heavy pellets-same fps). Positive thing, even less recoil (weird). the strangest thing when I opened the transfer port hole was when I put a .125" drill bit through the transfer port hole I would have expected it to go straight into the combustion chamber. It didn't. It went in about 3/4 the way and stopped like there was something blocking it on the combustion chamber side. I first drilled with the .125" bit all the way through ( should of stopped and checked there) but I got the other bit out and opened her up.

For what its worth, I think the lighter piston in a gas ram is better.2 reasons:
1) no loss in fps
2) reduced recoil

[john]

Excerpt from the latest in a long series of "technical" articles published monthly in the current issue of Airgun World:

"Reducing the length of the piston stroke is but one of the numerous modifications that people carry out to improve their spring air rifles, along with varying the mainspring and preload, varying the effective piston mass, altering the diameter of the transfer port, and more. Every modification has an effect on the shot cycle, but any perceived improvement comes at the price of less than desirable side effects."

The author and his cronies have taken up where the Cardews left off. Pretty good reading for shade tree physicists.

 

[Laser-Fist]

So do we agree that reduced recoil is an overall improvement? The force that a ram exerts is most likely consistent throughout its stroke, the piston is less likely to bounce off the cushion of air when lightend because the ram is still exerting significant force. Aren't we all ultimately looking for a smoother shooting cycle? -Craig

[Privateer]

So do we agree that reduced recoil is an overall improvement? The force that a ram exerts is most likely consistent throughout its stroke, the piston is less likely to bounce off the cushion of air when lightend because the ram is still exerting significant force. Aren't we all ultimately looking for a smoother shooting cycle? -Craig

I'd agree to that statement due to the fact a ram maintains a higher constant extended force in all states.
A spring has variable amounts of pressure and is highly prone to rebound.
Take the shocks off the front of your car once to see this effect first hand if you need a good example.

Now using the shocks on a car is a queer way to explain what I'm thinking as those are actually 2 way rams.
They have a some what neutral point and reduce rebound in both directions.

I can see a reason to mod weights in a springer due to the rebound effect.
In a gas piston? I can't see any reason other then just taking weight off the Gun.
And that is probably a waste of time for what you gain.

[OleTomCat]

So do we agree that reduced recoil is an overall improvement? The force that a ram exerts is most likely consistent throughout its stroke, the piston is less likely to bounce off the cushion of air when lightend because the ram is still exerting significant force. Aren't we all ultimately looking for a smoother shooting cycle? -Craig

I'd agree to that statement due to the fact a ram maintains a higher constant extended force in all states.
A spring has variable amounts of pressure and is highly prone to rebound.
Take the shocks off the front of your car once to see this effect first hand if you need a good example.

Now using the shocks on a car is a queer way to explain what I'm thinking as those are actually 2 way rams.
They have a some what neutral point and reduce rebound in both directions.

I can see a reason to mod weights in a springer due to the rebound effect.
In a gas piston? I can't see any reason other then just taking weight off the Gun.
And that is probably a waste of time for what you gain.

Not everyone is looking for a smoother shot cycle per say some want more power regardless of the recoil, by lightening the piston you reduce the energy transferred to the pellet...

[aidave]

I hadn't considered less moving mass for less felt recoil -- but that sounds worth it to me, during the winter when I won't be shooting much; take my time to cut out some mass, and chamfer/bevel everything nice and smooth.  even a slight drop  in fps wouldn't bug me, since it would probably help with lighter pellets.
Something to think about...
thank you for your input.

[Laser-Fist]

If the force exerted from the ram is constant, and enough weight remains in the modified piston, there will probably be little to no loss in Velocity. There will be a loss in felt recoil, less mass needs to slow down/speed up. Again I am going to modify and confirm over the summer months. -Craig

[OleTomCat]

They are easy enough to get from Crosman and less than $20.00 with a new seal already installed do go for it and let us know how it worked...

[shorty]

As far as my experiences go with the lighter piston, It did reduce recoil but did not increase fps and shot cycle appeared faster. Like I said earlier, I used a cut off wheel on my air grinder. No drill bit of mine would touch the metal. I say go ahead. Hack it up. a piston is fairly cheap to replace. I think the way I cut mine also reduced metal to metal contact (less friction) because I hacked off the top of the piston in a large area.
Its kind of funny how that "dang" gas piston works. Completely different than a spring.

What fun would this be if there wasn't people hacking up the stuff to make things better or adversely improving something we didn't expect. Just be safe doing it and think it through.

Everyone has crazy ideas and some work. If you have never done it " the lightening of the piston on a gas ram" all comments are theory only. Theory's are good and are very welcome. It really helps making that first cut decision.

[robtmc]

If the force exerted from the ram is constant, and enough weight remains in the modified piston, there will probably be little to no loss in Velocity.

What would be fascinating is instrumenting the compression chamber right at the port into the barrel and recording the pressure rise rate and amplitude.  They do this for firearms all the time when proofing guns and new ammo chamberings.

Would think that would answer most questions about what the effect is of less piston mass.

[Paul68]

If the force exerted from the ram is constant, and enough weight remains in the modified piston, there will probably be little to no loss in Velocity.

What would be fascinating is instrumenting the compression chamber right at the port into the barrel and recording the pressure rise rate and amplitude.  They do this for firearms all the time when proofing guns and new ammo chamberings.

Would think that would answer most questions about what the effect is of less piston mass.

It's easy enough to gauge the effect using a chrony. You simply shoot a ten shot string using the guns favorite pellet, then make your mods, then shoot another string and compare the numbers.

[shorty]

Robtmc has a good point to measure the psi at the transfer port hole. It would be great to measure BUT, too many dynamic things going on. I don't think Paul 68's idea of the chrony would be accurate either. When the piston comes forward and begins its compression, the pellet moves forward through the barrel before maximum psi is achieved. This in turn changes the volumetric area of the total combustion chamber (not measureable now). Its almost the same reason why two different 14 grain pellets can have a 50 -70 fps difference. More resistance in the chamber.

Finding out how much psi is generated in the combustion chamber is interesting though and would be cool to know what affects it. there must be some kind of way of doing it.

What would be even better than changing piston weight would be changing compressable air in the combustion chamber before the piston even moves. What I mean is compressing a small amount of air in the combustion chamber when the piston is in the "ready to fire" position. this would be like a supercharger or turbo increasing allowable compressable air without increasing the mechanical area of the combustion chamber. Way high fps "I think". Just day dreaming
so it would be like a cross between a pump and gas ram rifle. Pretty cool idea.

[Paul68]

Robtmc has a good point to measure the psi at the transfer port hole. It would be great to measure BUT, too many dynamic things going on. I don't think Paul 68's idea of the chrony would be accurate either. When the piston comes forward and begins its compression, the pellet moves forward through the barrel before maximum psi is achieved. This in turn changes the volumetric area of the total combustion chamber (not measureable now). Its almost the same reason why two different 14 grain pellets can have a 50 -70 fps difference. More resistance in the chamber.

Finding out how much psi is generated in the combustion chamber is interesting though and would be cool to know what affects it. there must be some kind of way of doing it.

What would be even better than changing piston weight would be changing compressable air in the combustion chamber before the piston even moves. What I mean is compressing a small amount of air in the combustion chamber when the piston is in the "ready to fire" position. this would be like a supercharger or turbo increasing allowable compressable air without increasing the mechanical area of the combustion chamber. Way high fps "I think". Just day dreaming
so it would be like a cross between a pump and gas ram rifle. Pretty cool idea.

The point is to measure the effect lightening has on the power produced by the rifle in a realistic and practical manner. Shooting the same pellets in each test, once before, and once after, will give a VERY accurate account of how your modifications have effected the actual performance of the rifle. Since the only variable changed would be the piston weight, any effect on performance would be directly attributable to this change.