GTA
All Springer/NP/PCP Air Gun Discussion General => European/Asian Air Gun Gates => German AirGun Gate => Topic started by: byhsu on March 24, 2021, 08:32:09 PM
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i put my piston with the seal on and it goes down by gravity. It seems too lose for me. But then I cover the little hole on the outside of the receiver with my finger and turned the receiver up, the piston stayed in place and didn't fall out. Does that mean the Pistol seal fit is good?
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Which gun, and which seal (Brand - ARH, Vortek, Weihrauch, etc.) does this pertain to?
Also, what lube did you use on the seal and piston?
:D
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Which gun, and which seal (Brand - ARH, Vortek, Weihrauch, etc.) does this pertain to?
Also, what lube did you use on the seal and piston?
:D
The HW35E, original seal. I have not put any lube yet, just working on the internals first. Honda M77 Paste will be the lubricant. Thanks
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In my experience, it usually requires a finger push to get the piston to slide down, not just gravity. That being said, the ultimate test is a chrony reading.
If your testing the fit without lube, then yeah, it may just fall on its own, but I've never done it that way. I always just go ahead and lube it first.
More experienced people will certainly chime in, I'm sure.
:D
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Sliding by gravity is fine on a Weihrauch oe seal. The outer lip expands from the air pressure and creates a tight seal. They are commonly called parachute seals for this reason. Is this a new seal or one being reused? Make sure that the seal has no cuts in it from the cocking slot or body threads. Also on a loose fitting seal use very little moly behind the seal and absolutely none in front. Loose seals don't have great lubricant control and are sensitive to the slightest excess lubricant. Use just a little too much and it will get in front of the seal and detonate. Then you'll likely need a new seal and have shortened the life of the spring.
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Sliding by gravity is fine on a Weihrauch oe seal. The outer lip expands from the air pressure and creates a tight seal. They are commonly called parachute seals for this reason. Is this a new seal or one being reused? Make sure that the seal has no cuts in it from the cocking slot or body threads. Also on a loose fitting seal use very little moly behind the seal and absolutely none in front. Loose seals don't have great lubricant control and are sensitive to the slightest excess lubricant. Use just a little too much and it will get in front of the seal and detonate. Then you'll likely need a new seal and have shortened the life of the spring.
Thank You, So i guess a tighter fitting seal is actually better than a seal that fits a little loose then? It is the original seal. I took the gun apart, the seal seems fine.
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That seal looks well....ok....to me. I don't see any scars on the edges or the typical circumferential split or crack inside the outer lip.
What Ron was describing is that the "parachute' design creates a tight seal upon compression of the stroke, so there is nothing wrong with that design. Some other (non-parachute design) seals do not expand outward, and so need to be sized to fit tight without the power compression of the spring. Sizing a seal for proper fit is a rather difficult thing to do.
Personally, whenever I have a Weihrauch apart, I replace the OE seal with either a JM, or more recently, the Vortek Vac-Seal. Pretty much every Weihrauch that I taken a part had some flaw in the seal, be it a clip or cut in the lip, or that circumferential split.
What ever you do, be sure to de-burr the inside of the cocking slot with a half-round jewelers file. I buy mine from the hobby shop and you can get a whole set of sizes and shapes of files for about ten bucks. I use the one that is half-round on one face and flat on the other.
And then be very careful about re-fitting the new seal when re-inserting. It really doesn't take much to nick the lip of the seal.
:D
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Sliding by gravity is fine on a Weihrauch oe seal. The outer lip expands from the air pressure and creates a tight seal. They are commonly called parachute seals for this reason. Is this a new seal or one being reused? Make sure that the seal has no cuts in it from the cocking slot or body threads. Also on a loose fitting seal use very little moly behind the seal and absolutely none in front. Loose seals don't have great lubricant control and are sensitive to the slightest excess lubricant. Use just a little too much and it will get in front of the seal and detonate. Then you'll likely need a new seal and have shortened the life of the spring.
Thank You, So i guess a tighter fitting seal is actually better than a seal that fits a little loose then? It is the original seal. I took the gun apart, the seal seems fine.
from the pictures the seal looks fine. Tighter isn't always better. There's different designs and they all have there points. That seal maybe loose because of the seal or the bore. If it was making good power beforehand, reuse it. Just don't go nuts with the lube, you'll regret it. Here's the results of somebody's idea of a "lube tune". They smothered the thing with grease and moly to lubricate and dampen the spring noise. It eventually got in front of the piston and detonated until it burned a hole in the piston seal and collapsed the spring.
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Piston seals need about 2lbs of pressure to push in the tube! seals that fall under their own weight of the piston are way to lose IMO, and will cause damage to the rifle, I've had a few new out of the box HW rifles with seals that were to lose or under sized, on 1 of my rifles it actually cracked the stock after 30 shots test firing it! If use a seal that needs to be sized I leave it a tic tight because they will break in on their own! JMO 8)
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Lots of great info here learned the hard way ! pay attention and learn from others and you should be GTG
kindly
ron
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I've had a few new out of the box HW rifles with seals that were to lose or under sized, on 1 of my rifles it actually cracked the stock after 30 shots test firing it!
Gotta wonder if an undersized factory seal was the reason my HW95L's stock cracked in two places within the first 100 break-in shots, using mid-weight quality pellets and proper cocking / shooting technique. They replaced the stock free of charge, once I presented the evidence with some mighty heavy words, but things were a bit tense for awhile, having invested over 400 euros into my first high-quality airgun ever. Since then, I've learned how even 400 doesn't give you a problem-free pellet shooter. Gotta go for the 600-euro LGV for that.
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Sliding by gravity is fine on a Weihrauch oe seal. The outer lip expands from the air pressure and creates a tight seal. They are commonly called parachute seals for this reason. Is this a new seal or one being reused? Make sure that the seal has no cuts in it from the cocking slot or body threads. Also on a loose fitting seal use very little moly behind the seal and absolutely none in front. Loose seals don't have great lubricant control and are sensitive to the slightest excess lubricant. Use just a little too much and it will get in front of the seal and detonate. Then you'll likely need a new seal and have shortened the life of the spring.
Thank You, So i guess a tighter fitting seal is actually better than a seal that fits a little loose then? It is the original seal. I took the gun apart, the seal seems fine.
Something no one has mentioned:
Question: Are those two "dark dimples" a "footprint" of the TP?
If so, that gun is clearly oversprung for that design of gun/seal.
JMHO
HM
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Sliding by gravity is fine on a Weihrauch oe seal. The outer lip expands from the air pressure and creates a tight seal. They are commonly called parachute seals for this reason. Is this a new seal or one being reused? Make sure that the seal has no cuts in it from the cocking slot or body threads. Also on a loose fitting seal use very little moly behind the seal and absolutely none in front. Loose seals don't have great lubricant control and are sensitive to the slightest excess lubricant. Use just a little too much and it will get in front of the seal and detonate. Then you'll likely need a new seal and have shortened the life of the spring.
Thank You, So i guess a tighter fitting seal is actually better than a seal that fits a little loose then? It is the original seal. I took the gun apart, the seal seems fine.
Something no one has mentioned:
Question: Are those two "dark dimples" a "footprint" of the TP?
If so, that gun is clearly oversprung for that design of gun/seal.
JMHO
HM
The two dark dimples next to each other on the same radius is a print of the transfer port. The smaller dark dimple opposite of those on a different radius is remnants of the molding process. Pour stub. All these traits are common on most Weihrauchs. Especially higher output guns that have been dieseling. Which I suspect by the looks and the loose rotation of the seal on the piston.
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Could this also be a byproduct of shooting to light a pellet??
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When you cover the transfer Port with your finger AND press the piston down, is there much resistance? It should fight you the whole way, IE not move. >:(
-Y
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The two dark dimples next to each other on the same radius is a print of the transfer port. The smaller dark dimple opposite of those on a different radius is remnants of the molding process. Pour stub. All these traits are common on most Weihrauchs. Especially higher output guns that have been dieseling. Which I suspect by the looks and the loose rotation of the seal on the piston.
Yes, the dark dimples are the transfer port, opposite one could be from the molding, as it is a little above the rest of the seal.
Now the reason I opened her up was because I was getting some shots about 2 inches either high or low, don't know now which is the actual zero of the gun, as is sometimes high and sometimes low, I have not really been able to tell which point of impact corresponds to the zero.
I do not have that problem with my other rifles HW97k .22, R1 .22, HW30s .177, HW50s .177.
Could the loose fitting seal be the cause of the problem? maybe too much recoil slamming on the receiver tube that is causing my shots to go high or Low?
before I took the HW35 apart it was shooting the Crosman Premier HP 7.9gr .177 at about 800fps, JSB RS 7.33gr at 860fps, JSB exact 8.44gr at 790fps and the H&N FTT at 784fps.
I don't mind slower velocity as long as the rifle is accurate, but so far it is not.
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When you cover the transfer Port with your finger AND press the piston down, is there much resistance? It should fight you the whole way, IE not move. >:(
-Y
when i cover the transfer port with finger, and push down there is some resistance, but still goes down and if i flip the receiver upside down it won't fall down due to gravity.
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Replace the seal. If you can push it down, even slowly with your finger over the port its no good. Shifting POI can be a seal problem. Replace the seal. Definitely. I wasn't aware of these two conditions.
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I thought you were just doing a tune and all was well before hand.
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Pushing a piston with a lose seal by hand that has pressure and holds at the TP is not the same as a spring that has several hundred PSI of pressure when moving the piston
forward! ;)
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Replace the seal. If you can push it down, even slowly with your finger over the port its no good. Shifting POI can be a seal problem. Replace the seal. Definitely. I wasn't aware of these two conditions.
so definitely the conclusion is that the seal is too loose, correct?
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I thought you were just doing a tune and all was well before hand.
well, basically wanted to check out what is going on inside the rifle, why I am having accuracy issues, but since I have her open, yes, I am tuning her too.
Just made a plastic piston sleeve, deburred the cocking slot, will be polishing the outside of the spring as soon as i can get a hold of some 1200 grit sandpaper, found some online at Harbor Freight, will go check it out.
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What does polishing the outside of the spring do? I just don't remember hearing of anyone doing that.
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With the seal on the loose side, not holding pressure and POI shift. I would definitely replace it. After you take it off, press on the face of the seal and see if it reveals a split on the backside. Sometimes the seal will split in circular pattern that isn't easily detected on the face of the seal statically. When this happens it will seal to wide varying degrees and cause POI shifts. With this condition the bypassing pressure through the face of the seal balloons out seal diameter and the seal will spin easily. Brand new unfired seals can be turned by hand but should have some resistance
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What does polishing the outside of the spring do? I just don't remember hearing of anyone doing that.
Makes it look smooth and shiny? i don't know, i was given that advice by SpiralGroove.
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With the seal on the loose side, not holding pressure and POI shift. I would definitely replace it. After you take it off, press on the face of the seal and see if it reveals a split on the backside. Sometimes the seal will split in circular pattern that isn't easily detected on the face of the seal statically. When this happens it will seal to wide varying degrees and cause POI shifts. With this condition the bypassing pressure through the face of the seal balloons out seal diameter and the seal will spin easily. Brand new unfired seals can be turned by hand but should have some resistance
no split on the backside, maybe my tube is slightly out of round? probably using a bigger than 30mm seal will solve the problem of fitting too loose.
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I thought you were just doing a tune and all was well before hand.
well, basically wanted to check out what is going on inside the rifle, why I am having accuracy issues, but since I have her open, yes, I am tuning her too.
Just made a plastic piston sleeve, deburred the cocking slot, will be polishing the outside of the spring as soon as i can get a hold of some 1200 grit sandpaper, found some online at Harbor Freight, will go check it out.
your local auto parts store will have your sand paper in stock
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The bore is probably fine. I'd just get a new seal. Everyone has their preferred seals. I've used the JM and Weihrauch parachute seals and the Vortek seals. The Vortek seals are a cupped seal design and not a parachute design. I think JM has a second line of seals of this design as well as another company in Australia that are supposedly very good. I get the most power and life out of the Vortek. I just changed out one in my Hw95 that I installed in 2016 and probably has ten thousand plus rounds through it. They are a hard moly impregnated rubber. They are initially very tight so lots of people here whine about that. After a day or two of shooting they conform to the bore and loosen up. It's pretty common for the gun to pick up 20-40 fps from when first installed. Just changing to this design over a parachute design makes more power with no ill effects on the shot cycle. This will start a s-storm of opinions. You can do what you want this is just my actual experience.
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No visible scraping inside the bore where the seal rides?
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I thought you were just doing a tune and all was well before hand.
well, basically wanted to check out what is going on inside the rifle, why I am having accuracy issues, but since I have her open, yes, I am tuning her too.
Just made a plastic piston sleeve, deburred the cocking slot, will be polishing the outside of the spring as soon as i can get a hold of some 1200 grit sandpaper, found some online at Harbor Freight, will go check it out.
your local auto parts store will have your sand paper in stock
Went to Harbor Freight and got the 1200 grit sandpaper $2.99 for 7 sheets 9"x11", good price.
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No visible scraping inside the bore where the seal rides?
no signs of scraping, i shone a light and was like a mirror.
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What does polishing the outside of the spring do? I just don't remember hearing of anyone doing that.
Makes it look smooth and shiny? i don't know, i was given that advice by SpiralGroove.
I heard of polishing the ends of the spring where they ride on the guide/thrust washer and the tophat/piston but never heard of polishing the outside of the spring.... maybe a misunderstanding.
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The bore is probably fine. I'd just get a new seal. Everyone has their preferred seals. I've used the JM and Weihrauch parachute seals and the Vortek seals. The Vortek seals are a cupped seal design and not a parachute design. I think JM has a second line of seals of this design as well as another company in Australia that are supposedly very good. I get the most power and life out of the Vortek. I just changed out one in my Hw95 that I installed in 2016 and probably has ten thousand plus rounds through it. They are a hard moly impregnated rubber. They are initially very tight so lots of people here whine about that. After a day or two of shooting they conform to the bore and loosen up. It's pretty common for the gun to pick up 20-40 fps from when first installed. Just changing to this design over a parachute design makes more power with no ill effects on the shot cycle. This will start a s-storm of opinions. You can do what you want this is just my actual experience.
I am considering the Australian Eco 30mm seal or the Vac Seal. Which one comes oversized? I rather get a tighter fitting seal than a loose seal.
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What does polishing the outside of the spring do? I just don't remember hearing of anyone doing that.
Makes it look smooth and shiny? i don't know, i was given that advice by SpiralGroove.
I heard of polishing the ends of the spring where they ride on the guide/thrust washer and the tophat/piston but never heard of polishing the outside of the spring.... maybe a misunderstanding.
Below is a quote from Spiral Groove:
I usually sand the entire outside, spring length.
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What does polishing the outside of the spring do? I just don't remember hearing of anyone doing that.
Makes it look smooth and shiny? i don't know, i was given that advice by SpiralGroove.
I heard of polishing the ends of the spring where they ride on the guide/thrust washer and the tophat/piston but never heard of polishing the outside of the spring.... maybe a misunderstanding.
Below is a quote from Spiral Groove:
I usually sand the entire outside, spring length.
Wow... well, you know what they say... life is full of firsts. ;)
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What does polishing the outside of the spring do? I just don't remember hearing of anyone doing that.
Makes it look smooth and shiny? i don't know, i was given that advice by SpiralGroove.
I heard of polishing the ends of the spring where they ride on the guide/thrust washer and the tophat/piston but never heard of polishing the outside of the spring.... maybe a misunderstanding.
Below is a quote from Spiral Groove:
I usually sand the entire outside, spring length.
Wow... well, you know what they say... life is full of firsts. ;)
this is my first time tuning my own rifle, so I am picking up whatever they recommend, I just hope to resolve my issue with the accuracy.
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Yeah Guys,
I just make sure the spring slides nicely in the plastic sleeve. This maybe overkill, but I'm usually pretty anal about making sure nothing has been missed ::).
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I don't doubt you Kirk. I know you know your way around an airgun... just never heard that before.
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Yeah Guys,
I just make sure the spring slides nicely in the plastic sleeve. This maybe overkill, but I'm usually pretty anal about making sure nothing has been missed ::).
I don't mind sanding it either, as long as it's gonna shoot good is worth a try, plus my spring fits kind of tight inside the plastic sleeve so seems like a good idea to me.
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I'm sure Kirk told you that alot of things go towards accuracy from a springer... pellet choice and hold being a big part of it. Even a perfectly tuned gun and miss the target with the wrong pellet or hold.
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The bore is probably fine. I'd just get a new seal. Everyone has their preferred seals. I've used the JM and Weihrauch parachute seals and the Vortek seals. The Vortek seals are a cupped seal design and not a parachute design. I think JM has a second line of seals of this design as well as another company in Australia that are supposedly very good. I get the most power and life out of the Vortek. I just changed out one in my Hw95 that I installed in 2016 and probably has ten thousand plus rounds through it. They are a hard moly impregnated rubber. They are initially very tight so lots of people here whine about that. After a day or two of shooting they conform to the bore and loosen up. It's pretty common for the gun to pick up 20-40 fps from when first installed. Just changing to this design over a parachute design makes more power with no ill effects on the shot cycle. This will start a s-storm of opinions. You can do what you want this is just my actual experience.
I am considering the Australian Eco 30mm seal or the Vac Seal. Which one comes oversized? I rather get a tighter fitting seal than a loose seal.
I'm not familiar with the Australian one. The Vortek one as I said start off very tight so I'm sure it would work fine.
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The bore is probably fine. I'd just get a new seal. Everyone has their preferred seals. I've used the JM and Weihrauch parachute seals and the Vortek seals. The Vortek seals are a cupped seal design and not a parachute design. I think JM has a second line of seals of this design as well as another company in Australia that are supposedly very good. I get the most power and life out of the Vortek. I just changed out one in my Hw95 that I installed in 2016 and probably has ten thousand plus rounds through it. They are a hard moly impregnated rubber. They are initially very tight so lots of people here whine about that. After a day or two of shooting they conform to the bore and loosen up. It's pretty common for the gun to pick up 20-40 fps from when first installed. Just changing to this design over a parachute design makes more power with no ill effects on the shot cycle. This will start a s-storm of opinions. You can do what you want this is just my actual experience.
I am considering the Australian Eco 30mm seal or the Vac Seal. Which one comes oversized? I rather get a tighter fitting seal than a loose seal.
I'm not familiar with the Australian one. The Vortek one as I said start off very tight so I'm sure it would work fine.
do you have a picture of the cup design? so i can compare how they look like?
I did get a Venom Power Pulse Seal before for my HW97K when I had it tuned, but i can't remember how it looked like, that was 15 years ago.
Thanks
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I'm not at home so I grabbed this from their site. You can see it's cupped but has no parachute groove and lip
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I'm not at home so I grabbed this from their site. You can see it's cupped but has no parachute groove and lip
Vac-Seal 30mm is the one I need?
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I'm not at home so I grabbed this from their site. You can see it's cupped but has no parachute groove and lip
Vac-Seal 30mm is the one I need?
Yes it doesn't list the Hw35 but it will work. It's the same as the Hw80
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I'm not at home so I grabbed this from their site. You can see it's cupped but has no parachute groove and lip
Vac-Seal 30mm is the one I need?
Yes it doesn't list the Hw35 but it will work. It's the same as the Hw80
Great, thanks. That cup design seems to offer some cushion and prevent the piston slamming against the wall of the transfer port. Am i correct in my assumption, seems the parachute type is flat in the middle section.
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I'm not at home so I grabbed this from their site. You can see it's cupped but has no parachute groove and lip
Vac-Seal 30mm is the one I need?
Yes it doesn't list the Hw35 but it will work. It's the same as the Hw80
Great, thanks. That cup design seems to offer some cushion and prevent the piston slamming against the wall of the transfer port. Am i correct in my assumption, seems the parachute type is flat in the middle section.
It would be logical to assume that. If the piston slams into the transfer port sometime is terribly wrong. There would have to be a terribly bad sealing situation going on or a dry fire. When the piston comes forward squeezing all the air behind the pellet the pressure builds up and the piston slows down on a cushion of air and sinks to the end of its stroke as the pellet moves forward and relieves the pressure. This is an oversimplification of what happens. Sometimes if there's too much resistance (the pellet is too heavy or fits too tight) the piston will squeeze all the air so tight it bounces backwards. Sometimes several times. It's really a very fine balance of forces. Usually the best shooting pellets for a gun are the ones that offer the right resistance. A bouncing piston induces pulsating pressure that is detrimental to accuracy. Also too light a pellet or too loose and there's too little resistance and there's little to no air cushion and the shot cycle is abrupt and harsh. There's a lot going on in there and a lot of cool stuff to learn but there's a lot of good people to help you along.
To your original question there's nothing really wrong with the Weihrauch parachute design. The flat face isn't an issue as pointed out above. I just find I get better sealing, more power and longer life out of the Vortek VAC seals.
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Now the reason I opened her up was because I was getting some shots about 2 inches either high or low, don't know now which is the actual zero of the gun, as is sometimes high and sometimes low, I have not really been able to tell which point of impact corresponds to the zero.
Pablo,
At what range was this +- 2" shift? Did you try more than one type of pellet to see if they are all similarly affected? If at less than 25 yards, it may not be due to velocity variations from a bad seal:
If all the work you have done does not resolve your point of impacts shifting, I wonder if it is possible that the barrel lockup is varying, and affecting the angle of the barrel relative to the action when shut? +- 2" sounds like a lot of variation, unless the pellet velocity is extremely unstable. And odd, for shifting between two positions:
The barrel latch may not move freely. If it sticks a little it may cause the barrel to lock up in two distinct positions. You might want to see if the speed and force with which you close the breech correlates with the shifting point of impact. If might be that a little moly grease on the latch related sliding surfaces fixes that, should the latch be sticky or suspected of being sticky. Of course, you could take the latch apart and lightly polish the tunnel is slides in. I would start with just checking and lubing it...
Usually, the first thing I would check if there is unstable point of impact would be the stock screws. Then the sight attachment screws. After you reassemble the action to the stock, the stock screws should be good. If the instability returns, first check the stock screws. Don't forget the sight screws...
I may be in the minority, but if with the original piston seal, the piston could hang vertically when you blocked the transfer port, that was sealing pretty well. Especially if one considers that the direction is backwards, and that sealing can only improve on the forward stroke as the parachute lip seal opens. That said, A tighter seal might have more wear life before it starts to leak. But by your description, you did not have a leaking piston seal.
While you have your airgun open, you might consider installing a slightly snug fitting spring guide. That has a huge effect on reducing spring twang. With just the right fit, that can increase pellet velocity a little, rather than reducing it.
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Man, a lot of great advice in this thread.
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When you cover the transfer Port with your finger AND press the piston down, is there much resistance? It should fight you the whole way, IE not move. >:(
Yogi,
The piston has to move before it will build pressure. It should "fight" you after you get half way down the stroke. The pressure generated should not dissipate rapidly. Assuming you manage to keep the TP blocked off.
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When you cover the transfer Port with your finger AND press the piston down, is there much resistance? It should fight you the whole way, IE not move. >:(
Yogi,
The piston has to move before it will build pressure. It should "fight" you after you get half way down the stroke. The pressure generated should not dissipate rapidly. Assuming you manage to keep the TP blocked off.
Subs, he's been having issues with this gun a while and Pablo has had a few threads on it so you're missing some information. Check out reply 15 on this thread https://www.gatewaytoairguns.org/GTA/index.php?topic=184310.msg156105656#msg156105656 (https://www.gatewaytoairguns.org/GTA/index.php?topic=184310.msg156105656#msg156105656)
With a 300 fps extreme spread where the high is the normal velocity there's a problem other than lock up and stock screws. Until this information came forth I suggested the same attention as you.
Switching gears. After reviewing this thread something caught my attention and you said that the sleeve was kind of tight and sanding the spring may improve fit. Pablo don't sand your spring for sleeve clearance. Polishing the spring may reduce friction but won't really change the fit significantly. You may need to use a thinner sleeve material. A spring will expand about 0.007" when compressed. It needs room to grow. To give you an idea of 0.007" it's roughly 3 sheets of loose leaf paper. Unless your sleeve is made of a compressible material you should have some clearance between your sleeve and spring.
I do agree with Subs that you should look hard into you lock up components while you have the gun apart. I wish I could be of more help with this but I'm unfamiliar with the unique locking system in the Hw35.
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When you cover the transfer Port with your finger AND press the piston down, is there much resistance? It should fight you the whole way, IE not move. >:(
Yogi,
The piston has to move before it will build pressure. It should "fight" you after you get half way down the stroke. The pressure generated should not dissipate rapidly. Assuming you manage to keep the TP blocked off.
Agreed, but you should feel increased resistance shortly after pushing the piston down. Yes, the more you push, the more resistance... ;D
-Y
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With a 300 fps extreme spread where the high is the normal velocity there's a problem other than lock up and stock screws.
Thanks, Ron
300 FPS spread will shift the POI, but 4"? Of course, the range at which the POI shift occurs would help answer that.
So, it certainly could be the piston seal. Or a sticky breech latch that not only shifts the muzzle up or down, but when down it leaks air at the breech seal and reduces the velocity (so leaky breech seal, due to poor lockup). Such intermittent leaks (lack of cushioning) would also explain the TP mark on the piston face...
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We have a winner: Based on the link Ron provided (see Pablo quoted below), barrel latching is inconsistent, with the wedge occasionally failing to drop fully into lockup. This may be due to excessive barrel hinge tension, making it hard to feel the breech close properly. Or Pablo is closing the breech too gently. Or too fast - such that the barrel bounces partly open before the latch can drop home.
Or, the breech seal may be too tall, and is interfering with breech closure. Or the latch has some roughness in its channel. Or its spring has a sharp coil at the moving end. I rest my case :)
Only oil i've added is to the barrel lock latch. It was not closing smoothly and twice i've put the rifle on the shooting bag and the barrel got open and i fired without knowing it.
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With a 300 fps extreme spread where the high is the normal velocity there's a problem other than lock up and stock screws.
Thanks, Ron
300 FPS spread will shift the POI, but 4"? Of course, the range at which the POI shift occurs would help answer that.
So, it certainly could be the piston seal. Or a sticky breech latch that not only shifts the muzzle up or down, but when down it leaks air at the breech seal and reduces the velocity (so leaky breech seal, due to poor lockup). Such intermittent leaks (lack of cushioning) would also explain the TP mark on the piston face...
You're absolutely correct but I'm trying to address one thing at a time here, which is the internals of the gun. Once that's ironed out and we can address other issues. The guy has the guts apart already, so the horses have left the barn already and I'm just trying to get them back in. Correctly.
IIRC this gun accidentally popped open twice while being fired because the lock wasn't in place. This would be similar to a dry fire and would account for a damaged piston seal. The TP print incidentally happens on ever Weihrauch seal I've seen. I didn't want to argue with Hector. The fact that the seal is burned and the TP print moved is more important. This implies that the gun has been dieseling severely. Which I don't know the exact reason but after a gun diesels badly or detonates the following shot drops a couple hundred fps. This too fits the occasional very wide ES previously experienced.
The current issue is the oe seal is too loose, leaks pressure too quickly and needs to be replaced. Let's just get the guts back together right and out of the equation because he already has to.
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Let's just get the guts back together right and out of the equation because he already has too.
Yes. Can't diagnose anything with it all in bits.
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Now the reason I opened her up was because I was getting some shots about 2 inches either high or low, don't know now which is the actual zero of the gun, as is sometimes high and sometimes low, I have not really been able to tell which point of impact corresponds to the zero.
Pablo,
At what range was this +- 2" shift? Did you try more than one type of pellet to see if they are all similarly affected? If at less than 25 yards, it may not be due to velocity variations from a bad seal:
If all the work you have done does not resolve your point of impacts shifting, I wonder if it is possible that the barrel lockup is varying, and affecting the angle of the barrel relative to the action when shut? +- 2" sounds like a lot of variation, unless the pellet velocity is extremely unstable. And odd, for shifting between two positions:
The barrel latch may not move freely. If it sticks a little it may cause the barrel to lock up in two distinct positions. You might want to see if the speed and force with which you close the breech correlates with the shifting point of impact. If might be that a little moly grease on the latch related sliding surfaces fixes that, should the latch be sticky or suspected of being sticky. Of course, you could take the latch apart and lightly polish the tunnel is slides in. I would start with just checking and lubing it...
Usually, the first thing I would check if there is unstable point of impact would be the stock screws. Then the sight attachment screws. After you reassemble the action to the stock, the stock screws should be good. If the instability returns, first check the stock screws. Don't forget the sight screws...
I may be in the minority, but if with the original piston seal, the piston could hang vertically when you blocked the transfer port, that was sealing pretty well. Especially if one considers that the direction is backwards, and that sealing can only improve on the forward stroke as the parachute lip seal opens. That said, A tighter seal might have more wear life before it starts to leak. But by your description, you did not have a leaking piston seal.
While you have your airgun open, you might consider installing a slightly snug fitting spring guide. That has a huge effect on reducing spring twang. With just the right fit, that can increase pellet velocity a little, rather than reducing it.
very good points to consider, specially regarding the barrel locking. a few times i laid the rifle on the shooting bag and it popped open without me noticing, since I was looking thru the scope.
I did make a plastic piston sleeve from a plastic bottle. Spring fits real tight, but i've sanded it down so it just fits snug now. I will probably sand it a little bit more, so when the spring is compressed it goes in smoothly into the piston.
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Now the reason I opened her up was because I was getting some shots about 2 inches either high or low, don't know now which is the actual zero of the gun, as is sometimes high and sometimes low, I have not really been able to tell which point of impact corresponds to the zero.
Pablo,
At what range was this +- 2" shift? Did you try more than one type of pellet to see if they are all similarly affected? If at less than 25 yards, it may not be due to velocity variations from a bad seal:
If all the work you have done does not resolve your point of impacts shifting, I wonder if it is possible that the barrel lockup is varying, and affecting the angle of the barrel relative to the action when shut? +- 2" sounds like a lot of variation, unless the pellet velocity is extremely unstable. And odd, for shifting between two positions:
The barrel latch may not move freely. If it sticks a little it may cause the barrel to lock up in two distinct positions. You might want to see if the speed and force with which you close the breech correlates with the shifting point of impact. If might be that a little moly grease on the latch related sliding surfaces fixes that, should the latch be sticky or suspected of being sticky. Of course, you could take the latch apart and lightly polish the tunnel is slides in. I would start with just checking and lubing it...
Usually, the first thing I would check if there is unstable point of impact would be the stock screws. Then the sight attachment screws. After you reassemble the action to the stock, the stock screws should be good. If the instability returns, first check the stock screws. Don't forget the sight screws...
I may be in the minority, but if with the original piston seal, the piston could hang vertically when you blocked the transfer port, that was sealing pretty well. Especially if one considers that the direction is backwards, and that sealing can only improve on the forward stroke as the parachute lip seal opens. That said, A tighter seal might have more wear life before it starts to leak. But by your description, you did not have a leaking piston seal.
While you have your airgun open, you might consider installing a slightly snug fitting spring guide. That has a huge effect on reducing spring twang. With just the right fit, that can increase pellet velocity a little, rather than reducing it.
very good points to consider, specially regarding the barrel locking. a few times i laid the rifle on the shooting bag and it popped open without me noticing, since I was looking thru the scope.
I did make a plastic piston sleeve from a plastic bottle. Spring fits real tight, but i've sanded it down so it just fits snug now. I will probably sand it a little bit more, so when the spring is compressed it goes in smoothly into the piston.
I'm out. Good luck to you.
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Put back the HW35E with a new Vortek Vac-seal 30mm piston seal, built a piston sleeve with a plastic bottle and deburred all the sharp edges and put Moly to lube the internals. Now the rifle is very consistent. I zeroed it today and started target shooting at 20 yards, now I can pretty much hit what I aim at. I think the Seal did the trick, but I also made sure all the screws were tight and the latch was polished and has a positive lock up everytime. Also that liner does make the rifle shoot with NO twang at all.
As for velocities, I've only tested it with Crosman 7.9 gr avg. 767fps and JSB 8.44 gr 750 fps. Before tune it was 807 fps for 7.9gr and 790fps for 8.44gr. Not too concerned with FPS as Accuracy is more important for me in this rifle, with 750 fps I think I'm good for my regular shooting range of 20 yards and I think even if I went 40 yards it would be OK.
Also it doesn't seem to have as much recoil as before and the rifle is more accurate for sure. I actually did my target shooting today with the 7.9gr, but i think with the JSB it would probably group better.
I am very happy with the rifle now. Thank You everyone for your advice.
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If the new seal was tight going in it'll probably pick up a velocity as it conforms to the bore. Also a too tight a sleeve to spring fit will slow a gun down. See what happens. All that counts is the POI and velocity is consistent and you're happy.
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Yes, the Seal did fit tight. As for the Sleeve, I redid how it was attached, originally there were tabs folding out that were hooked at the opening of the piston, so they were impeding the steel sleeve from expanding when the spring was fitted, so it was tight. I polished the spring and also I made a new sleeve with tabs that folded in and were placed at the bottom of the sleeve and they were retained by a metal washer (3/4") with 3/8" opening, so now the spring fits in perfect.
I no longer feel the piston slamming into the internals of the rifle when I fire, I was getting that with the old piston seal because it was fitting too loosely and it would slide down with gravity, this new piston seal won't slide down with gravity, I have to push it in.
Firing cycle is very nice now, and It is more accurate, even with the Cheap Crosman Premier Hollow Points.
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Yes, the Seal did fit tight. As for the Sleeve, I redid how it was attached, originally there were tabs folding out that were hooked at the opening of the piston, so they were impeding the steel sleeve from expanding when the spring was fitted, so it was tight. I polished the spring and also I made a new sleeve with tabs that folded in and were placed at the bottom of the sleeve and they were retained by a metal washer (3/4") with 3/8" opening, so now the spring fits in perfect.
I no longer feel the piston slamming into the internals of the rifle when I fire, I was getting that with the old piston seal because it was fitting too loosely and it would slide down with gravity, this new piston seal won't slide down with gravity, I have to push it in.
Firing cycle is very nice now, and It is more accurate, even with the Cheap Crosman Premier Hollow Points.
Excellent. Good news. POI steady now?
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Yes, pretty much, I will test it again this coming weekend when I get a chance. Thanks for the recommendation on Vortek Seals, I like the cup style and that they fit a little more snug, the OEM seal on mine was undersized.