GTA
Airguns by Make and Model => Weihrauch Airguns => Topic started by: Bob H. on February 19, 2021, 11:07:47 AM
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Hi Folks,
I saw the Short Stroke Piston Seals on 'bay. Has anybody tried them in their Weihrauchs? When they are back in stock, I want to try one in my Hw30. I would like to hear your experiences with these long seals.
Thanks,
BobH.
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Bob, I'm using those seals in most of my HW's 26mm guns, I always purchase more then 1 at time, I find these seals are pretty much a drop in seal, the reason I buy at least 2 is because 1 might fit a little snugger then the other, I have not had to size any of them and I have not had any that were under sized either, IMO I think these are decent piston seals ;D
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Mark,
I thank you for your input. Perhaps you can guide me along. Does the extra length of the seal dampen the impact of the piston hitting the end of the stroke? I would think that the reduced travel of the piston would lower the velocity of the pellet. I'm trying to turn my Tyrollean stocked R7 (Hw30) into a poor man's 10MM air rifle. Looking for less velocity and a softer cycle.
BobH.
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JMO I think u also need to tune the rifle to work along with the piston being stroked, by reducing its power! ;D
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Mark,
I have yet to tune a spring gun. I have no idea when custonairseals will have a 25mm short stroke seal in stock. I think that they do their own manufacturing.
There may need to be more detuning done. I would like to end up at about 550 -575 fps. I haven't a feel for how the short stroke seal will effect the R7's velocity.
BTW are the short stroke seal difficult to install?
Thanks,
BobH.
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is it just a seal? or a seal that has an adapter? ::)
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Looks like a long seal to me
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Artie,
Thank you for posting the photo.
BobH.
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I think you will need other modifications to use that seal.
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I think you will need other modifications to use that seal.
You should be able to use it without any modifications. Whether or not the rifle would be better if you modified other parts in concert with the change of stroke is a different story. The only thing the longer seal changes mechanically (besides the stroke) is shortening the springs installed length. Thus increasing preload. The springs compressed length and pressure remain the same as with the OE seal. This is very intriguing I'd like to see how much difference this makes.
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I was talking to OC about these when I seen them, as he was making some of his own. These should snap right on the piston. The only change I can think of is when you break open the barrel, it will fall farther before the slack is taken up between the cocking arm and the piston. My HW30 with the Vortek kit at 10m will give my FWB300's a good run for the money,
Jason
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I think you will need other modifications to use that seal.
You should be able to use it without any modifications. Whether or not the rifle would be better if you modified other parts in concert with the change of stroke is a different story. The only thing the longer seal changes mechanically (besides the stroke) is shortening the springs installed length. Thus increasing preload. The springs compressed length and pressure remain the same as with the OE seal. This is very intriguing I'd like to see how much difference this makes.
Ok, I don’t get it. The seal is way taller/longer, won’t it slam into the end of the chamber?
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The piston will slam into the end of the chamber regardless. With the short stroke seal there will be less swept volume, decreased cocking stroke, lower power, and likely a "snappier" firing cycle.
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The piston will slam into the end of the chamber regardless. With the short stroke seal there will be less swept volume, decreased cocking stroke, lower power, and likely a "snappier" firing cycle.
Technically the piston only slams the end of the chamber when the gun is dry fired. When it's loaded there's enough resistance that the air can't exit the chamber quick enough to for the piston to slam into the end. That resistance creates a high pressure cushion of air that the piston pushes against until the air finally exits and the piston sinks to the end of the chamber. It happens so fast it may sound and feel like it slams but it don't. In fact the piston often bounces off the air cushion multiple times before the air fully leaves. This is why dry firing spring guns is a good way to break them. If that piston slammed the end as one might think, people like NCED couldn't run full metal pistons with only o-ring seals.
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I stand corrected and do agree, ideally a piston should not slam.
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You may want to look at this?
https://www.youtube.com/watch?v=ZwC9qRjFZlk (https://www.youtube.com/watch?v=ZwC9qRjFZlk)
If you short stroke you should also reduce the spring pressure, either cut coils or use a lighter spring.
-Y
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I am no expert when it comes to using any method of stroking a rifle like this, but my common knowledge tells me and I could be very wrong but if ur adding more length to the piston, that seal looks pretty long at least 11mm, which is going to change ur stack height of ur spring and as mentioned preload, depending on how much more preload can be added to the to the spring before it stacks up? before its to much and the trigger will not engage or lock up? The reason I say this is I have OC HW98, it has a stroker set up on the piston, it also has a R10 compression tube that has a longer stroke then the HW95/R9 tubes, I took this rifle apart first thing I noticed is the spring was not a full length spring, It was missing about 4 coils, I do not know if he did that for the power level he was looking for or other reasons? I replaced the spring with a JM Hornet 120dia wire that JM uses in his HW50 spring kits, The rifle functions perfectly but the barrel does fall a little bit further when breaking it open vs a full power spring, The velocity with a 7.9gn CPHP is around 725fps with the spring I put in it, its a fantastic shooting and very accurate rifle ;)
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Good video Yogi 8)
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Good video Yogi 8)
When I had my HW 50 short stroked, John in Pa said he had to cut 9 coils off.... :D
-Y
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Short stroking a springer is done to reduce its power, without increasing its lock-time (time lapse from trigger releasing piston, to pellet starting to move - or, more strictly speaking, leaving the muzzle). It is harder to shoot a springer well if it has a sluggish piston, compared to one with a short shot cycle.
The R7 / HW 30 is already very easy to shoot well. If you short stroke it and take just enough preload out of the spring to maintain its lock-time (or shorten it slightly), the air rifle should be just as easy or a little easier to shoot well.
Strictly speaking, you could leave the spring full length. If you think about it, too long a spring results in coil-bind when cocked. Spring room when cocked is unchanged with the long seal. What will have changed is swept volume (down); and spring preload when uncocked. The latter will increase the amount of force on the spring clamp, when installing the spring.
The increased preload in the fired state may increase piston slam, due to the reduction in swept volume. Then again, there is less travel distance for the piston to pick up speed. In any event, if installing the long seal causes harshness not previously there, then reducing the spring preload is probably indicated.
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Thanks Subscriber for explaining coherently what I intended to say. :D
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Guys,
I'm soaking up your replies with great interest.
Let propose doing this. I increase the seal length by 12MM (.472")and the spring is .106 wire and 28.5 coils long. If I cut 2 coils off, that roughly keeps the spring at the same compression when the rifle is not cocked. When the rifle is cocked there is now less tension on the spring. The piston travel is now .480" shorter. Now the piston should have a lower terminal velocity and a smaller quantity if air is being force into the barrel. To me, it seems reasonable the velocity of the rifle should be less. The forward inertia of the piston should be less because the square of the velocity is less, a gentler shot cycle. The above would be my starting point of first attempt.
Am I seeing this correctly? (Clear as mud at midnight)
BobH.
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Bob,
Cutting off as much spring length as you are adding with the long seal seems like a natural thing to do. Cut off less, rather than more; because putting it back is tricky :)
If you like that minimalist change in length, then you leave it be. If the shot cycle seems harsh, you take off half as much length as before.
You may be able to some fine adjusting with spacers. Your rifle may have one or more in it from the factory.
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Short stroking a springer is done to reduce its power, without increasing its lock-time (time lapse from trigger releasing piston, to pellet starting to move - or, more strictly speaking, leaving the muzzle). It is harder to shoot a springer well if it has a sluggish piston, compared to one with a short shot cycle.
The R7 / HW 30 is already very easy to shoot well. If you short stroke it and take just enough preload out of the spring to maintain its lock-time (or shorten it slightly), the air rifle should be just as easy or a little easier to shoot well.
Strictly speaking, you could leave the spring full length. If you think about it, too long a spring results in coil-bind when cocked. Spring room when cocked is unchanged with the long seal. What will have changed is swept volume (down); and spring preload when uncocked. The latter will increase the amount of force on the spring clamp, when installing the spring.
The increased preload in the fired state may increase piston slam, due to the reduction in swept volume. Then again, there is less travel distance for the piston to pick up speed. In any event, if installing the long seal causes harshness not previously there, then reducing the spring preload is probably indicated.
Perfect analysis! To reiterate The long seal DOES NOT CHANGE compressed length. It can’t induce coil bind or increase compressed pressure. The only thing it changes is preloaded. Subsequent effects are best determined with actual experiments. Lock time will be reduced will it be harsh or not? You can guess all days long and you still won’t know until someone actually does it. It’s why I’m interested in following the thread. Someone said something to the effect, a thousand expert hypotheses isn’t worth one good experiment.
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Bob don’t cut anything until you try the seal alone. You’re inducing more unknowns and variables. It maybe perfect for you without cutting. It takes 10 minutes (or less) to get the spring out of the rifle for cutting. The bulk of the work is changing the seal. If it’s too harsh uncut take a coil off at a time until you like it. Very easy gun to work on.
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I was talking to OC about these when I seen them, as he was making some of his own. These should snap right on the piston. The only change I can think of is when you break open the barrel, it will fall farther before the slack is taken up between the cocking arm and the piston. My HW30 with the Vortek kit at 10m will give my FWB300's a good run for the money,
Jason
When I started with break barrels 4 years ago, it was difficult in the beginning to adopt the safe loading practice of holding the cocked barrel when loading. I have grown used to it now through repetition. But it is still easier at the bench than standing in the field. I have always wondered if a slightly more open break on a Break-Barrel would allow for a break-load-cock sequence rather than the current break-cock-load with hand on barrel sequence. Good to know it is possible with a short stroke seal!
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Thanks Guys,
The project will start when we start seeing 40 degree temperatures in the corn fields. It's tough to do good work when you are shaking from the cold.
While I'm waiting for the short stroke 25MM seal to become available, I may try to make my own. I have some nylon, other similar materials, and an old Logan lathe.
I used to be just stubborn, now I'm old and stubborn.
Again, thank you for your input, feel free to add more thoughts.
BobH.
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I would agree with Ron and subs, this is a topic I have not read up on or have done myself, so I'm curious to find ur results, without going thru what ur about too, we can only give our thoughts and insight on what may or may not occur, I personally do not tune for big power anymore unless its power plant larger the an R9/HW95 tube, and stroking the piston my be of some use on my smaller tubes like my HW50's and 95 size guns? 8)
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Interesting subject.
I have one of the short stroke piston adapters that OC made for a Diana 28mm piston and have been tempted to try it in my 54 but I like it the way it is.
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Folks,
The temperature in the corn field have risen above 40 degrees. This week I found some 1"dia. delrin and turned a seal adapter for my Hw30 / R7. The adapter adds 1/2" of length to the piston assembly. Re-assembling using the original seal and spring gave a velocity of 535 fps using CPHP pellets.
At 10 meters, the trigger pull to target flight duration seems to about the same as it was before. The felt recoil is less and the rifle is a bit more stable off hand. I suspect the elapsed time of the piston travel is less and the I know terminal velocity of the piston is less. For what I wanted to achieve, the results are positive.
What I learned was the delrin adapter had to pressed on and was very difficult to pry off the piston button. I need to change some diameters that I used in machining the adapter. There are assuredly better materials to use for the adapter, but I will keep experimenting with what i have. Did I say that I was stubborn?
BobH.