is it the seals

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   that's a variable question. are you after the pressure that spring will impart to pellet which so far I've found to be ( in limit research so far) 30% of the spring energy. The actual pressure if there was no air port which probly need a formula, or the pressure of the cylinder that is needed to start the pellet which from memory is about 1200 (don't quote me on that)
rechecked Here's the info from download below

The pressure in the chamber does not begin to build up significantly until the piston is about 1/2 inch from the end of the chamber. At this point, the pressure goes up dramatically from around 120psi to 1200 psi at 1/10th inch from the end when the piston stops. This dramatic increase is only because the pellet is totally blocking the escape of any air. At around 1200psi, the pellet releases it's grip and accelerates up the barrel. Without the pellet, there will not even be close to enough pressure to stop the piston so the piston will slam into the end of the chamber.
Which leads me to the question, if your precharging a chamber will it hold the piston back, and if so when firing will the piston then travel the rest of the way creating shock/recoil. If so will it be less? 

Edited by kruzaroad - 27 Aug 2022 at 8:18am

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kruzaroad Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 02 Jul 2022 Location: Hastings 4 now Status: Offline Posts: 1686	Post Options Post Reply Quote kruzaroad Report Post Thanks(0) Quote Reply Posted: 27 Aug 2022 at 7:40am
	that's a variable question. are you after the pressure that spring will impart to pellet which so far I've found to be ( in limit research so far) 30% of the spring energy. The actual pressure if there was no air port which probly need a formula, or the pressure of the cylinder that is needed to start the pellet which from memory is about 1200 (don't quote me on that) rechecked Here's the info from download below The pressure in the chamber does not begin to build up significantly until the piston is about 1/2 inch from the end of the chamber. At this point, the pressure goes up dramatically from around 120psi to 1200 psi at 1/10th inch from the end when the piston stops. This dramatic increase is only because the pellet is totally blocking the escape of any air. At around 1200psi, the pellet releases it's grip and accelerates up the barrel. Without the pellet, there will not even be close to enough pressure to stop the piston so the piston will slam into the end of the chamber. Which leads me to the question, if your precharging a chamber will it hold the piston back, and if so when firing will the piston then travel the rest of the way creating shock/recoil. If so will it be less? Edited by kruzaroad - 27 Aug 2022 at 8:18am

kruzaroad Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 02 Jul 2022 Location: Hastings 4 now Status: Offline Posts: 1686	Post Options Post Reply Quote kruzaroad Report Post Thanks(0) Quote Reply Posted: 27 Aug 2022 at 7:47am
	https://www.mediafire.com/?5mcemcyutrm Pdf of book "Trigger to muzzle" comprehensive study of internal workings of springer air guns. More formulas for working out stuff that you can shake a stick at. Older study by 3 independent guys. Equations all relevant to modern springers guns if you have the input data. Edited by kruzaroad - 27 Aug 2022 at 7:48am

Pauly5 Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 10 Mar 2013 Location: Titahi Bay Status: Offline Posts: 1176	Post Options Post Reply Quote Pauly5 Report Post Thanks(0) Quote Reply Posted: 27 Aug 2022 at 8:45am
	You would need a non return valve between piston chamber and plenum to store the pressurized air, or else the benefit of the "swept volume" with piston momentum is lost, and then you've really only got a single stroke Pneumatic

kruzaroad Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 02 Jul 2022 Location: Hastings 4 now Status: Offline Posts: 1686	Post Options Post Reply Quote kruzaroad Report Post Thanks(0) Quote Reply Posted: 27 Aug 2022 at 10:34am
	One shot is all you will get out of a standard size springer set up. It's all I'm looking at. The increase in volume for doing multiple shots I have no dought would be to large and heavy. The addition of a larger storage chamber for high pressure would facilitate the ability for more than one shot but need multiple pumps. Im working on the principle of springer convenience of one pump, no outside precharging and getting rid of the recoil while shooting. If you want to increase the air chamber size for more than one shot your going to need custom seals, custom piston, custom receiver. I'm trying for the idea adapting a cheap air rifle for experimentation for proof of concept. What diameter air chamber do you think is the largest you can go without getting to big and I'll look at the volumes and pressure, see how much air a single pump will store under pressure and volume, the increase of friction over seal diameter, increase of heat through port to high pressure chamber, increased piston weight (though design could drop that) extra force needed to cock the barrel, etc etc, but I dought it will be more than two or three at max. Thats if you don't want to do that yourself. You will never get the volume storage of a pcp ( which is highly compressed from machinary using multiple compression strokes) in a single stroke action (in my view) but you can get enough for high pressure storage for a single shot from what I've looked at so far and even that may require a larger cylinder diameter or longer piston stroke to over come the loss of energy compressing into chamber. Havent worked all that out yet. Anyone who wants to and post results please do.

kruzaroad Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 02 Jul 2022 Location: Hastings 4 now Status: Offline Posts: 1686	Post Options Post Reply Quote kruzaroad Report Post Thanks(0) Quote Reply Posted: 30 Aug 2022 at 9:31am
	Happy days. Barrel just arrived. Wish he had left the cocking arms on as they are pressed over on ends. Still barrel rifling looks clean and crisp and most importantly there is no dirty great gouge around the rifling. You can guess what I'm upto now. Hopefully be posting a few targets that are tighter in groups later today. Edited by kruzaroad - 30 Aug 2022 at 9:37am

Billbobnz Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 13 Jun 2020 Location: Ashburton Status: Offline Posts: 778	Post Options Post Reply Quote Billbobnz Report Post Thanks(0) Quote Reply Posted: 30 Aug 2022 at 10:33am
	Awesome, let us know how it shoots

kruzaroad Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 02 Jul 2022 Location: Hastings 4 now Status: Offline Posts: 1686	Post Options Post Reply Quote kruzaroad Report Post Thanks(0) Quote Reply Posted: 30 Aug 2022 at 4:22pm
	So barrel on, had to change rear sight blade as the fiber optic wire was broken on replacent. Haven't tested all of my pellets yet. Grouping much better 20m some nice tight performance from gun City Javelin. ftt held inside an inch but bit spread in that inch. AA field showed some promise. 25m changed the story. AA field to spread out. hornet shows promise. ftt bordering the edge of inch. Javelin OK will look at that again. white field had so many damaged pellets and such a thin skirt I didn't shoot them and won't buy them again. GAMO Pro magnum preformed awful and three pellets of the ten I selected wouldn't fit in barrel ( I guess with a hammer they would have) But the one that beat them all at 25m was stoeger x-field. An under dog that didn't preform in old barrel at all. The gun seems to like 14.66gr. ftt was the best performer with old barrel and is same gr. Did OK this time too. I'll run through the rest of tins tomorrow but for now I'm happy gun shoots at last

Billbobnz Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 13 Jun 2020 Location: Ashburton Status: Offline Posts: 778	Post Options Post Reply Quote Billbobnz Report Post Thanks(0) Quote Reply Posted: 30 Aug 2022 at 6:43pm
	That's an improvement. The guncity javelins and stoeger are made by H&N and I've had good success with them before. I've just replaced the breech seal with the new seal from custom air seals on my Hatsan .25cal and put two pellets into a tin can at 43yards first pop, will do the piston seal once I've got time but so far so good. Nothing worse than having a gun that your not sure if your going to hit something, and particularly with an animal that you could wound it

kruzaroad Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 02 Jul 2022 Location: Hastings 4 now Status: Offline Posts: 1686	Post Options Post Reply Quote kruzaroad Report Post Thanks(0) Quote Reply Posted: 30 Aug 2022 at 7:59pm
	true that. I imagine at 43 yards the .25 would have a good whack to it. I must try a larger cal one day. keep us informed of its progress Edited by kruzaroad - 30 Aug 2022 at 8:00pm

mercs Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 24 Apr 2020 Location: Stratford Status: Offline Posts: 243	Post Options Post Reply Quote mercs Report Post Thanks(0) Quote Reply Posted: 30 Aug 2022 at 8:17pm
	Nice result with the barrel change and the X-Field pellets. A frustrating journey but rifle now looks to be a genuine hunter with those groupings. I use the H&N Barracuda Match or H&N Hunter Extreme and H&N FTT are a reliable go-to. Interested how the Air Arms test as they are a well respected option. Never tried the Hornets so keen to see how they stack up. Full marks for perseverance and taking the time to share on the forum.