jai_landrover

Have tried preloading and re Oder spring the only affect was a twangy mess and no real power increase hence all the work

Indeed I can cut the piston down to gain all research suggests that an o ring will be over legal limit start long and cut down as neasasaey

Sorry for the poor pic phone pic not the best

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Right just got off the lathe we have a double o ring piston I have pics but need to upload then to imageshack first when I get home J

Best results so fr have been with this at 9 ft lbs its a Titan spring as supplied by welsh willy it's not loose but the spring must not be compressed any more than a mm when assembled. At the lathe now am about to spin up a new piston head see how it goes J

O ring is desirable due to cost and ease of field repair

I have tried it and got 4ft ft lbs no preload pn spring can double that with new type piston assy

Yes I have some nylon blocks I turn down but think Ali would be better. As it happens I unscrewed the seal after I posted and will indeed make several piston ends double and single o rings to try I'm in London today so may e able o pick up more material to play with. Lots of people mention limiting stroke to keep within the legal limit and I will not destroy the piston if I can get up close to the limit without having to re work it. Buttoning seems like a cleaver idea one which would be nice eventually the main thing is keeping it nice to shoot while getting 11.5 ft lbs or as close to 12 as possible with my chosen pellets yet to be decided. Been using pax guns own brand and had good results. I have no intention on getting 15 ft lbs and having a twangy mess to try and shoot. On a side note I'm quite happy as I tried rabbit yesterday for the first time all day in the slow cooker with loadsa stew and its just a variation on chicken which means I'm not wasting my time. The idea of getting the gun sorted is for a weekend away Offroad driving and only eating what you catch farmers permission beforehand of course as a kind of survival/green lane driving somewhere remote. Being totally self sufficient except vehicle fuel and water. Next stage is getting the gun up to power and then more practice at the range, eventually a rabbit or two and gutting and skinning. Slow as it might be we're getting there slowly!! J

To set my mind at ease my uncle has a PCP and we checked it with the chrono and it was bang on 11.7ft lbs so I know the Chrono is working. I think the next step forward is to use the leather type piston and modify it as its no use to me at 4Ft/lbs. I have a couple of O rings and will machine the end off the leather piston and weld in a new piston head giving maximum stroke and using an O ring. The question i'm now debating in my head is a single O ring or double with a 3mm gap between. The later may mean that I can not get much more cylinder volume. Any ideas or anyone with experience would be appreciated. I may well just make it one for now and see how it goes. still deciding.................... J

Ok more info I got a second hand old type leather piston complete from Ebay. The differences are the piston has a shorter stroke mainly due to the whole assembly being approx 6mm longer. I have just fitted and tried it as std and getting around 4ft lbs. there is also a difference in weight the new type with synthetic seal weighs in at 201g whereas the older leather type weighs in at 229g. Uploaded with ImageShack.us

Elliot What vehicle is it? I can send you details I think I posted a link before (nothing to do with me) but a friend that fits tracking systems. Jai

Cheers John, The Ali steel piston is purely a try out. I have got a second piston although the older leather type will compare to my piston assy. Will then machine off the piston head and make a new head with double O ring and increase its stroke as much as possible. Again as angry out. Have the old mans lathe and milling machine so seems like a bit of fun. I can't find anything fundamentally wrong with the gun cylinder is airtight, piston seal holds good pressure new breech checked or leaks and the max ingot with 14.5 Gr pellets was 9 Lbs feet. Still running the piston in o bed in but has had a hundred through it so will re chrono it later. I think an O ring piston is the way forward. I understand the twangy mess you describe I had that with all the spacers fitted and you can't hit a barn door now it's lovely and accurate with almost zero recoil just a few more lbs ft req before safe quarry kills.

Cheers John, The Ali steel piston is purely a try out. I have got a second piston although the older leather type will compare to my piston assy. Will then machine off the piston head and make a new head with double O ring and increase its stroke as much as possible. Again as angry out. Have the old mans lathe and milling machine so seems like a bit of fun. I can't find anything fundamentally wrong with the gun cylinder is airtight, piston seal holds good pressure new breech checked or leaks and the max ingot with 14.5 Gr pellets was 9 Lbs feet. Still running the piston in o bed in but has had a hundred through it so will re chrono it later. I think an O ring piston is the way forward. I understand the twangy mess you describe I had that with all the spacers fitted and you can't hit a barn door now it's lovely and accurate with almost zero recoil just a few more lbs ft req before safe quarry kills.

Tomorrow I'm marshalling a trials comp before the nationals unfortunatly my trials motor is not ready for this years mud but next year we shall be good to go!!