Don't shoot me down is a 50/50 Spring and Gas Ram Possible?

[tinbum]

Don't wish to contradict Tin but I have been fitting needle roller thrust bearings for a while to counteract spring torque, if you have a rotating piston it makes little difference although it does help, I have tested this back to back, but on a non rotating piston like a HW77 it makes a big difference to the lateral movement of the rifle.

I test the bearings by firing the rifle at a 1cm square grid at 10yds, I aim at a highlighted point and freeze in place after the shot , then measure the distance the crosshair has come of target, do this ten times to get an average reading, fit the bearings and run the test again, in every case the bearings reduced lateral movement to practically nil, you can actually feel the difference.

It's not contradicary, just another approach. As for testing, I just shoot and watch the crosshairs. I'm not saying rollers dont work, or rotating pistons. But roller bearings are susceptible to getting crud in them and a rotating piston with a slip washer works better than a rotating piston alone. And if people want to fit roller bearings at the rear then it can only help. 🙂

[Muskett]

Both ends seems a good idea.

[Artfull-Bodger]

Once you allow either end of the spring to rotate feely then there is no benefit to adding a second bearing, I have tried this.

One problem is bearing size, because of the standardisation of sizes you can only fit a needle bearing on the spring guide of a rifle with a tube diameter of 28mm and above (BSA, HW77/97 etc), so on anything smaller the bearing has to go into the piston, I don't ideally want to do this as it adds weight obviously so you have to be able to set the weight of the piston if your working around a lightened piston, but the benefits outweigh the negatives.

When the bearing goes on the spring guide I make the guides with a precise seat at the base for the bearing to sit on, the spring then locates on the hardened washer of the bearing, the important bit is guide to spring fit, some people like to use a tight fitting guide, well that won't work with the bearing as the spring must be able to rotate on the guide without restriction, so I make the spring guide in aluminium and a precise sliding fit into the spring.

I have tried Delrin and different steels but after talking to an aerospace guy about resonance he mentioned the dissimilar frequency approach, basically steels resonate at similar frequencies, so making a guide in alloy interrupts the resonance so you get a similar damping effect to delrin but a much stiffer installation, also alloy has good abrasion resistance, after all pistons in car engines are alloy and go up and down millions of times in their life cycles.

If the bearing has to go into the piston then I make up a top hat that locates the bearing under it and sits again on a hardened washer, and again the spring must be able to move without binding.

So the installation requires a slightly different approach but once you figure it out it works extremely well, Tinbum mentioned crud getting in, whilst I understand the concern so far I have had bearings in my HW77 (three years) and my HW98 (two years) I strip the rifle and inspect the bearings every six months or so and neither are showing any signs of wear, with no pitting or witness marks in the bearing, but if you think about it that's expected as a delrin spacer or top hat survives without splitting so a lubricated hardened bearing should have no problem.

[Rickenbacker]

To fit a rear thrust bearing - You have to machine a bit off the trigger block doncha? I know that's what big tony did to a 77K of mine, plus he fixed a spring guide in the trigger block.

Damn, that gun was good too... you've convinced me Arty, I need thrust bearings in all my '77s.

[Artfull-Bodger]

When you fit the spring guide into the trigger block you can machine the seat for the bearing on the guide, this then also becomes the depth stop for the guide in the block, so you don't need to machine the rear block other than to allow the guide to be inserted.

[oldskoolzzz]

Save me creating a new thread thought I’d bring back this one from 6 years ago

This stupid idea of a 50/50 Spring/ram has been on my mind for many many years.

I probably already know it’s a completely flawed idea from the start but what the heck I’m going to give it a whirl anyway

I’m going to be using a Webleysan (Webley VMX Hatsan in drag) as the test bed which seems ideal as it’s being totally stripped again whilst I work on some other bits it makes sense for some experimenting

Just need to source a few bits and bobs but hopefully I’ll start this crazy idea and report back what happens along the way.

Yep it’s probably got disaster written all over it but unless I get off my backside and at least try it that’s half the fun eh?

[oldskoolzzz]

No, a slim sealed unit with a wrap-around spring would be interesting to try. With the rams steady pressure at all times it could have a big effect on piston bounce

probably not, but I say go for it!

Finally going to give it a whirl Tinners

[cooper_dan]

Why not start with a theoben or HW90 and put a spring inside the ram?

[oldskoolzzz]

Why not start with a theoben or HW90 and put a spring inside the ram?

It’s a good shout Dan but the last time I buggered about with springs in those pukka rammers it left a sour taste

I don’t really have the budget for messing about with those setups buddy hence I’m going the cheaper route with something that doesn’t matter if it ends up a complete mess

[Neil54]

A spring in line with a ram wouldn't work in my mind as the ram would compress the spring flat.

Now a ram inside the spring perhaps as a guide could be onto something.
The ram I have to hand the body measures 18x151mm, with 3mm spring wire this would make 24mm.
I wonder what the piston internal diameter of a 28mm cylinder gun is.

[oldskoolzzz]

A spring in line with a ram wouldn't work in my mind as the ram would compress the spring flat.

Now a ram inside the spring perhaps as a guide could be onto something.
The ram I have to hand the body measures 18x151mm, with 3mm spring wire this would make 24mm.
I wonder what the piston internal diameter of a 28mm cylinder gun is.

Thanks for the reply Neil.

Yes I see what you are saying.

My plans involve two routes that I want to experiment with the ram inside a spring as you mention but also a shorter ram eg pistol type with a front spring as well.

The latter will probably not work but I’m intrigued to try it as the curiosity has finally got the better of me as it’s something I’ve been wanting to try for many many years.

Now I’ve got a suitable test bed all stripped ready I feel more confident of trying to see what works and what’s obviously not going to work.

This was going to be a winter project but I’ve started it earlier and hopefully should be getting the ball rolling soon whilst I gather parts and also do some other work.

I’m really intrigued to see how the shot cycle will fair as a dual setup it might be absolutely horrid but I’ll never know unless I give it a whirl

[tinbum]

Finally going to give it a whirl Tinners

Cool! And further to the mention of roller bearings at the back, we found a way to adapt rear guides allow the rear of the spring to spin too, even when the spring guide is a tight fit.

This has been a good thread

[robs5230]

Thanks for the reply Neil.

Yes I see what you are saying.

My plans involve two routes that I want to experiment with the ram inside a spring as you mention but also a shorter ram eg pistol type with a front spring as well.

The latter will probably not work but I’m intrigued to try it as the curiosity has finally got the better of me as it’s something I’ve been wanting to try for many many years.

Now I’ve got a suitable test bed all stripped ready I feel more confident of trying to see what works and what’s obviously not going to work.

This was going to be a winter project but I’ve started it earlier and hopefully should be getting the ball rolling soon whilst I gather parts and also do some other work.

I’m really intrigued to see how the shot cycle will fair as a dual setup it might be absolutely horrid but I’ll never know unless I give it a whirl

Talking from experience, as someone who converted a Theoben rammer to spring power, in the mid 90's, I'd say a spring within the ram is more logical than a spring outside a ram as you have the perfect space within the ram (Theoben or HW90 ram) to house a spring.
But I think the rate at which the air in the ram decompresses / expands, in relation to the expansion of the spring, may partly negate one or the other, as well as adding unwanted weight to the action.
Mildly curious, but only on a technical level

Springs have been used in conjunction with air or oil, in motorcycle / mountain bike shocks, for a long time, but the function of both is different to your intended use. In bike shocks, the springs provide the shock absorption and the oil/air, provides the damping (almost the reverse of what you want in a rifle).
In my experience with gas ram rifles, there is far less bounce (or felt bounce), so you're trying to create a solution, to a problem that doesn't exist.

As I said though Nick, interested.

[oldskoolzzz]

Cool! And further to the mention of roller bearings at the back, we found a way to adapt rear guides allow the rear of the spring to spin too, even when the spring guide is a tight fit.

This has been a good thread

Nice one re the guides Tinners.

Yes I agree been a good thread hopefully once I start experimenting I can add my findings.

Talking from experience, as someone who converted a Theoben rammer to spring power, in the mid 90's, I'd say a spring within the ram is more logical than a spring outside a ram as you have the perfect space within the ram (Theoben or HW90 ram) to house a spring.
But I think the rate at which the air in the ram decompresses / expands, in relation to the expansion of the spring, may partly negate one or the other, as well as adding unwanted weight to the action.
Mildly curious, but only on a technical level

Springs have been used in conjunction with air or oil, in motorcycle / mountain bike shocks, for a long time, but the function of both is different to your intended use. In bike shocks, the springs provide the shock absorption and the oil/air, provides the damping (almost the reverse of what you want in a rifle).
In my experience with gas ram rifles, there is far less bounce (or felt bounce), so you're trying to create a solution, to a problem that doesn't exist.

As I said though Nick, interested.

Cheers Rob,

Yes buddy I’m no stranger to spring converted Theobens done a couple myself few years back with mixed results.

I just honestly wondered if a dual setup ram and spring was actually achievable something I’d been thinking about and meaning to do for many years.

The idea sounds stupid and certainly bizarre on paper but it’s that I wonder what it would be like in practice curiosity 🤔

Unfortunately I’m fairly limited with my abilities as I’m certainly no engineer just a grease monkey who likes taking things apart and mending stuff with the pragmatic approach although I’ve a few good mates that are very handy with the lathe and engineering side if needed.

[Hsing-ee]

It sounds like the most expensive and painful Relum Tornado Revival possible. Two components storing energy and releasing it at different rates.

Sorry but it’s the answer to a question that hasn’t been formulated.