Can a heavy piston rob power?

[Waddy]

From what I've gleaned over the years about this it more comes down to the weight being suitable for sub 12 rifles. I had a lot of weight removed from the piston in my Hatsan 55 & then downsized the TP to make it cycle better at sub 12. It was horrible before, and way hot with a full length Titan spring too.

Not sure if this exactly the same with rammers, can't you just up the pressure in to make up for the power loss, which as you say is possibly more likely to be down to effectively short stroking it ?

[look no hands]

From what I've gleaned over the years about this it more comes down to the weight being suitable for sub 12 rifles. I had a lot of weight removed from the piston in my Hatsan 55 & then downsized the TP to make it cycle better at sub 12. It was horrible before, and way hot with a full length Titan spring too.

Not sure if this exactly the same with rammers, can't you just up the pressure in to make up for the power loss, which as you say is possibly more likely to be down to effectively short stroking it ?

At the moment it has a Diana N-tech drop in gas ram, as the original Theoben ram setup can't be used, as it was knackered before I got the gun as someone had converted it to a springer (very badly may I say) and I'm having trouble converting it back to a proper rammer, so putting more air in isn't possible at the moment.

[BTDT]

...too light also robs power, as the piston lacks inertia....

Inertia is a property of a stationary mass, Jon. A moving mass like a piston has momentum, and too light a piston reduces momentum.

[Born Again]

Inertia is a property of a stationary mass, Jon. A moving mass like a piston has momentum, and too light a piston reduces momentum.

Not quite. Splitting hairs, inertia is the tendency of an object to remain in the same state, either stationary or in uniform motion, resisting change.

[BTDT]

Not quite. Splitting hairs, inertia is the tendency of an object to remain in the same state, either stationary or in uniform motion, resisting change.

To really split hairs, inertia is a property of a moving mass only if that movement is uniform, which the piston is not - it's either accelerating or decelerating (apart from an instant before it bounces).

The important point is that it is the reduced momentum of the lighter weight piston that makes it less able to overcome opposition from the compressed air.

[Barryg]

Does AA put these things in an TXHC to raise or rob power, simple question

[look no hands]

Does AA put these things in an TXHC to raise or rob power, simple question

I'd say to raise power as they use the same spec spring for all calibres, it's so they can adjust the power easier, exactly the same idea that BSA use with washers in the Supersport/star.

[Barryg]

I'd say to raise power as they use the same spec spring for all calibres, it's so they can adjust the power easier, exactly the same idea that BSA use with washers in the Supersport/star.

So I guess the simple answer is that a heavy piston doesn't rob power unless using extremes

But just for fun I wonder what springer has the heaviest piston, my guess is a Patriot

[Born Again]

To really split hairs, inertia is a property of a moving mass only if that movement is uniform, which the piston is not - it's either accelerating or decelerating (apart from an instant before it bounces).

The important point is that it is the reduced momentum of the lighter weight piston that makes it less able to overcome opposition from the compressed air.

As momentum is a simple function of mass and velocity, it could be argued that the reduced inertia, and thus higher attained velocity of a lighter piston would give it enough momentum to compress the air.

It would be fascinating to see high speed x-ray film of the whole firing cycle, but until then we have to rely on the painstaking empirical research of you springer experts, for which I'm grateful.

[junglie]

I only ask as I'm sure I read JB's tuning of the Airsporter RB2 and he said the piston was too heavy, I was chronoing the Fenman last night and it is running at 10ftp with the drop in Diana gas ram, it was also doing the same with the spring kit I have, but that didn't have any preload slip washers fitted, I had a 5mm thick disk welded to the front of the Fenman piston so I could fit a Diana 35 seal, I first thought it might be too heavy but have just thought that it's been short stroked because of the longer seal and the added disk, so tat might be why it is lower power with spring fitted.

The RB does not need any help making power apart from winding out the restrictor screw in the transfer port in the roller breech, I had to take a coil or so off mine after that mod & new breech seals to keep it below 12.....(RB airsporter carbine in .22) felt slammy & not nice to shoot before, improved it no end & it was the best airsporter I ever shot by far & very accurate too with FTT's.

[look no hands]

The RB does not need any help making power apart from winding out the restrictor screw in the transfer port in the roller breech, I had to take a coil or so off mine after that mod & new breech seals to keep it below 12.....(RB airsporter carbine in .22) felt slammy & not nice to shoot before, improved it no end & it was the best airsporter I ever shot by far & very accurate too with FTT's.

How true yo are, I'm actually confusing the subject by quoting something that isn't connected to this problem, as you say the RB2 doesn't have a problem making power with a heavier than usual piston, JB said that reducing the pistons weight helped with recoil reduction and a smoother firing cycle, I apologise for any confusion caused.

[TonyL]

I only ask as I'm sure I read JB's tuning of the Airsporter RB2 and he said the piston was too heavy, I was chronoing the Fenman last night and it is running at 10ftp with the drop in Diana gas ram, it was also doing the same with the spring kit I have, but that didn't have any preload slip washers fitted, I had a 5mm thick disk welded to the front of the Fenman piston so I could fit a Diana 35 seal, I first thought it might be too heavy but have just thought that it's been short stroked because of the longer seal and the added disk, so tat might be why it is lower power with spring fitted.

I think I read somewhere that Theoben rammer pistons are hefty old lumps because they have thick walls as they have a lot of pressure in them, so most probably heavier than a standard springer piston, and because of the extra weight they need extra high pressure to propell them.

... which as you say is possibly more likely to be down to effectively short stroking it ?

Yep, taking this into account, in this case I think the lower output is, most likely, down to losing some of that stroke. Sounding like a big, heavy piston to begin with also, so is going to require some extra ooommpphh to get it working properly? Upping spring force should help in terms of, hopefully, finding that power and quickening up the cycle. A lighter piston with the standard stroke should help, also. But if you are not wanting / able to source another piston, I'd be looking to up the spring (obviously keeping in mind the firing cycle and usability).

[TonyL]

Does AA put these things in an TXHC to raise or rob power, simple question

I'd say to raise power as they use the same spec spring for all calibres, it's so they can adjust the power easier, exactly the same idea that BSA use with washers in the Supersport/star.

So I guess the simple answer is that a heavy piston doesn't rob power unless using extremes

:

As Pete says.

But it's so easy to generalise, as said earlier. Some guns might benefit from more piston weight, others not. It depends on the design, dimensions, desired power and characteristics etc.

In the case of the TX HC item, this longer / heavier top hat increases weight, and therefore momentum and also spring preload. Many tinkerers remove this heavy steel item and substitute for a lighter acetal item, giving very slightly less initial recoil from the first compression stroke and a "quicker" feeling cycle but have to increase preload to restore power as this usually drops, thus quickening up the cycle even more, due to quicker piston acceleration (lighter piston / increased spring force). That extra preload will also come into play to combat potentially greater piston bounce displacement.

[TonyL]

Inertia is a property of a stationary mass, Jon. A moving mass like a piston has momentum, and too light a piston reduces momentum.

To really split hairs, inertia is a property of a moving mass only if that movement is uniform, which the piston is not - it's either accelerating or decelerating (apart from an instant before it bounces).

The important point is that it is the reduced momentum of the lighter weight piston that makes it less able to overcome opposition from the compressed air.

Great to see you on, Jim.

[Dornfelderliebe]

I would like to experiment with a metal top hat to increase weight but don't how much one would weigh. Any rough Ideas for a 25-26 mm cylinder?

I'll be coy about which gun I'm thinking of.