Can a heavy piston rob power?

[Shed tuner]

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.

they are thick and heavy, and seem to need more stroke than expected too.. same with an HW90..

[look no hands]

they are thick and heavy, and seem to need more stroke than expected too.. same with an HW90..

So if it was converted back to spring, would a lighter piston help?

[Shed tuner]

So if it was converted back to spring, would a lighter piston help?

depends on the stroke / bore, but quite possibly, yes...

[look no hands]

depends on the stroke / bore, but quite possibly, yes...

Not sure on the stroke but it's a 28mm bore.

[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.

[Barryg]

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

[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).