Tuning Short Stroke Piston Seal ?

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harrympope said:
I wasn't arguing at all, but it was kind of funny. I've never heard anybody replacing Air Arms seals with HW.

How are you testing and monitoring "thermal expansion"?
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It's been a suspicion of mine for years and when I moved to Arkansas I had terrible problems when shooting my rifles for extended sessions in the hot sun. I noticed my velocities and groups tank. A fine gentleman from one of the UK forums explained what was happening.

Long before that I've noticed during testing in my temperature controlled basement that guns would slowly lose velocity during long sessions. After cooling off a while the first few shots were the fastest.

It's not much of an issue as I said earlier if you're a casual shooter in normal conditions. For those that shoot a lot or in sunny hot conditions it'll have you chasing your tail.
 
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Mycapt65 said:
It's been a suspicion of mine for years and when I moved to Arkansas I had terrible problems when shooting my rifles for extended sessions in the hot sun. I noticed my velocities and groups tank. A fine gentleman from one of the UK forums explained what was happening.

Long before that I've noticed during testing in my temperature controlled basement that guns would slowly lose velocity during long sessions. After cooling off a while the first few shots were the fastest.

It's not much of an issue as I said earlier if you're a casual shooter in normal conditions. For those that shoot a lot or in sunny hot conditions it'll have you chasing your tail.
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No humidity in my area but Temps go from sub zero to 115 in the summer
Winter months it takes a few shots for the spring guns to settle their zero I've noticed.
 
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harrympope said:
No humidity in my area but Temps go from sub zero to 115 in the summer
Winter months it takes a few shots for the spring guns to settle their zero I've noticed.
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I don't believe humidity is a major factor. Humidity here in Arkansas as well as lower NY is very high. I've always seen a a slight change of velocity and poi during prolonged sessions in lower NY. I didn't notice significant accuracy problems until I got to Arkansas. There the heat and or intense sunlight would wreak havoc after a hundred or so shots in fairly quick succession. There's always room for improvement.
 
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I've noted the commentary in UK forums about POI shifts due to temperature at the upper levels in FT. The commentary seems divided between shifting to O-rings and scope problems. Is there any downside to using O-rings? To me it would appear cost effective to manufacturing but there doesn't seem to be concerted effort by the AA, Weihrauch and Gamo or Cometa. It might be that compression tube diameter is not well enough controlled??
 
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Star7 said:
I've noted the commentary in UK forums about POI shifts due to temperature at the upper levels in FT. The commentary seems divided between shifting to O-rings and scope problems. Is there any downside to using O-rings? To me it would appear cost effective to manufacturing but there doesn't seem to be concerted effort by the AA, Weihrauch and Gamo or Cometa. It might be that compression tube diameter is not well enough controlled??
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I think controlling compression tube tolerance might be more expensive than using the parachute seals. I have to do a little more research on oring style seals. It would seam to me that they'd be less forgiving of irregularities than a lipped seal.
I believe going to a hollow Diana style seal would be an improvement over the Weihrauchs full cap style. Perhaps I'll machine a Weihrauch piston to accept bolt on hollow seal.
 
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JM at ARH has been tuning for a long time and has often commented about the poor tolerance control of various brands' compression tubes. I imagine that is why he provides seals slightly oversize so they can be fitted. What you are doing sounds sensible to me. I've seen referenses in UK forums that recent Weihrauch seals are worse than before. I don't have knowledge to know one way or the other.
 
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Star7 said:
JM at ARH has been tuning for a long time and has often commented about the poor tolerance control of various brands' compression tubes. I imagine that is why he provides seals slightly oversize so they can be fitted. What you are doing sounds sensible to me. I've seen referenses in UK forums that recent Weihrauch seals are worse than before. I don't have knowledge to know one way or the other.
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Weihrauch constantly flip flops between slightly different piston seals. Sometimes they are thin lipped and sometimes they are thick lipped. It's a random occurance. Probably whatever vendor gives them the best deal of can make enough of them at the time.
I use the Vortek seals and have pretty good luck with them until the hottest days of summer. I've tried thin lipped seals of various brands like JM and they are slightly less affected by thermal expansion but start off with less power. I think the issue is that the seals spans the whole bore which gives alot of material nowhere to expand but out against the tube walls.

Honestly my issues with thermal expansion can be minimized by rotating guns more often and keeping them out of direct sunlight. I would just like to develop a better piston seal that wouldn't be as affected by heat.
 
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harrympope said:
With all this talk about different seals, it all makes sense but my HW and Air Arms all shoot fantastic with ARH and factory seals.I seem to be accuracy issue,being the loose nut at the end of the stock.
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I'm splitting hairs on already fine rifles. Most people don't shoot as much as I do so they'll never have the same issues. I'd still like to improve them
 
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