I didn't know you add pressure to a gas ram??
After a while of looking at air rifles, all that were springers, I decided on the Hatsan MOD 65. I just feel like you can get more years out of them.
Upvote 0
Spring Piston vs. Gas Ram: Which is Your Preferred Powerplant?
- Thread starter JustNeedORingSize
- Start date
After a while of looking at air rifles, all that were springers, I decided on the Hatsan MOD 65. I just feel like you can get more years out of them.
Some you can "tune" some are factory sealed rams / as is.
My old hatsan mod25 can be adjusted with a hatsan fill port , but my Gamo is sealed.. kinda thing.
Upvote 0
All of the scope eating and harsher shot cycle from gas rams is due to poor design. Simply taking out the spring and placing a ram inside is the reason for all these issues.
I believe that a key problem with gas rams is also their strength - they have a shorter lock time because they decompress quicker and thus reach terminal speed faster than a spring. This results in very high peak compression. Ideally, this means that you need less air to expel the pellet at the same speed as you would with a spring design. Unfortunately, most gas ram designs kept the same long stroke (air volume) and heavy pistons that were needed by springers. This resulted in more power but also violent/short immediate recoil, as the mass of the piston and increased accelerate resulted in awful impact stress at the end of the compression cycle.
What the designers should have done is reduced the compression chamber diameter, reduced the piston mass, and optimized the transfer port diameter/length. Optimizing these variables would have resulted in less recoil, decent power, less cocking effort, and better accuracy than a springer.
I’m not sure if it’s been tried yet, but taking a Tony Leach kit and substituting its spring with a medium powered gas ram should provide most of the idealized benefits of a gas ram with less tendency to eat scopes. The most important questions/variables to answer with this swap would be the gas ram pressure and the diameter of the TP.
-Marty
Last edited:
Upvote 0
That is a fantastic idea. That would be an amazing gun. Not sure how that would work though. The piston rod is in the way
Last edited:
Upvote 0
Many gas rams have inversed action and thus low weight pistons and still are scope eaters
MMM
Upvote 0
I think most have inverted rams like in the pic below, but that is a small reduction in weight. In a springer only 1/3 of the spring counts toward the weight of the piston assembly. It’s the piston that needs to have its weight reduced for dramatic effects. Maybe there are some gas rams out there that have just a piston seal-end cap - not sure I’ve seen one yet…
-Marty
Upvote 0
Velocity has more of an impact on energy than piston weight does. A faster moving piston will
The older Theoben style rams (like the RX1) had basically zero ram weight in them, correct? The air was sealed between the piston and a sleeve that the piston rode on I believe.
Upvote 0
The Theobens, are a different story. I had an Eliminator/Crow-Mag with the H.E ram that has the anti-bounce weight inside and the ported piston seal - they were ahead of their time. Theoben really took gas ram design seriously.
That said, their design is still not optimum. In the photo of the Theoben Sirocco you posted above you can clearly see how massive the piston body is (its the lower left tube with piston seal attached on far-left side for those who are unfamiliar), the shiny piece on the right is just the end-plug of the ram. This is a better design than the Hatsan, Crosman and Diana N-Tec examples (see my earlier photo). Unfortunately, the mass of the Sirocco's piston is still too much. What I was suggesting is taking the inverted gas ram and putting the piston seal at the end of the stem, almost completely eliminating the massive piston body. This "stem piston" can then function inside a radius reduced compression chamber.
-Marty
Upvote 0
I don't believe so, since one side of the gas ram is both container and piston its moving mass counts toward the mass that is impacting the end of the compression chamber. Thats where all of the recoil was originating, mainly the mass of the piston side coming to an abrupt stop. The interesting thing to me is that if we take the F=MA formula we can get the same force out of the equation by reducing the mass and increasing the acceleration. I don't know exactly how much faster a ram is than a spring, but its enough to be noticeable. My best guess is that its more than 25%. Anyways, now combine this with the fact that you can reach peak compression faster with the same energy input if you downsize the compression chamber you can end up with less mass hitting the end of the comp tube/breech. Less mass = less recoil and better efficiency. Tony already proved that his kits are more efficient with a traditional spring and produce less recoil, but one has to wonder how much further they could be pushed with a gas ram...
-Marty
Upvote 0
What I am really confused by from the parts diagram is the red highlighted piece. I do believe I saw that during my tear down but it was inserted all the way into the piston and absolutely would add to the pistons weight. Any idea what it is?
Upvote 0
Yea, this Theoben design is special because the gas ram is both the piston and ram all in one. The yellow part is same as the stem in the other design. Compared to the stemmed gas ram pictured before, Theoben decided to make the stem closer to the diameter of the ram housing, and to further reduce complexity they also made the outer ram body into the piston. Its genius in its simplicity.
As to the special "red" piece, that's the inertia weight. I've looked at Theoben's patents a few years ago and I believe they were either trying to reduce piston bounce or create a very simplified Giss like system to cancel out some of the recoil. You can take a look at the inertia weights in the following PDF document.
-Marty
PS. The yellow part doesn't move as you said, so indeed it doesn't add to the weight, but it goes the other half which does move and that's where we need to remove mass. Making that other half out of titanium or some other light alloy would certainly help.
Last edited:
Upvote 0
A reduced piston weight will reduce recoil and pellet speed in a time. A too low piston weight won't be able to deliver high power. And a minimum of air cushion is necessary, too. Just don't know how much.
Upvote 0
This is the reason you also need to reduce the diameter of the compression chamber and increase the acceleration. This is exactly what Tony Leach did with his kit, albeit he did it with a stiff spring, a skeleton piston and a sleeves comp tube. Quicker peak compression maintains pellet speed up to a point.
-Marty
Upvote 0
The Hatsan I have leaked from pretty much new. The owner just replaced it and asked if i wanted it.
So I would charge it and get a weekend out of it, until it it wouldnt hold air at all. I have springers from the eighties that still shoot fine.
Upvote 0
That's the way you also can tame any springpiston. A smaller piston and reduced piston weight will reduce recoil and piston slam.
Maybe the gas ram has a point here for it can be smaller than the spring. But still there's a minimum swept volume to properly accelerate the pellet, in both cases the same depending on caliber and aimed speed. Just don't know how much exactly. But I think more than a century of airgunning will have evolved about the proper dimensions by just trial and error. What we are talking about now is just smaller corrections to the genuine design.
Maybe a short barreled Diana 48 @ 0.177 is overblown, or it surely is but a Beeman R7 @ 0.22" is surely underblown. Too little swept volume (with respect to the spring power) will always be dry firing
Upvote 0
many people say that the cocking effort of gas rams is heavy at the stroke's beginning. How come that?
Unlike a metal spring the compression force of which increases linearly with stroke the compressed air in the gas ram is supposed to show a force linear to about:
1/x+s-sa
where x is the volume of the compressed gas in the cocked state, s the complete stroke length and sa the actual stroke position. Or am I mistaken?
And then the cocking effort should increase way more than linearly with respect to the actual stroke position.
(Ideal gas behaviour provided, real gas is supposed to show even steeper force increase at the stroke end.)
Unlike a metal spring the compression force of which increases linearly with stroke the compressed air in the gas ram is supposed to show a force linear to about:
1/x+s-sa
where x is the volume of the compressed gas in the cocked state, s the complete stroke length and sa the actual stroke position. Or am I mistaken?
And then the cocking effort should increase way more than linearly with respect to the actual stroke position.
(Ideal gas behaviour provided, real gas is supposed to show even steeper force increase at the stroke end.)
Upvote 0
Ok, I get what you're asking. I only have experience with Theoben. The preload is greater with the ram. Don't know anything about the longer stroke strut types(converted springers)
Upvote 0