The 1st shot/Cold bore shot?

[nervoustrig]

I’d have to agree that a conventional unregulated PCP is the least susceptible to an errant first shot. However I have experienced it in the case where the valve body has an O-ring seal to the poppet stem. Whereas most PCPs simply use a slip fit so not susceptible to the breakaway friction of an O-ring.

Another example involved a valve stem that was bent ever so slightly. The rifle would hold a tight spread over a shooting session but any time it sat idle for a bit, the first shot was slow. At first I eyed the usual suspects like regulator creep and hammer friction. Eventually decided to remove the valve again and look harder. It was then I tried rotating the stem while pulling the poppet against the seat and was able to detect a slight hitch in the rotation. After making a replacement, the issue was completely gone.

Anyway, I consider these to be rare outliers...just something to consider if you ever run into a PCP that stubbornly refuses to give a good first shot.

 

[bustachip]

Hmmm. Idk.

As is "drop in" but set I hover around 835+850fps with cp-hp.177. now unset they can be hot at first till settled like 920+ , but eventually will settle in about 850 or so .. at least for me anyway.. I been well pleased with arh stuff and really never give the others much thought ..

Edit
Another quick 5 @ 50y ,irons, cp-hp a few min ago. I could say consistent?

View attachment 419448

Awesome for irons, you must still have eagle eyes..lol. I got into the airguns later and had to learn to shoot a scope with glasses, but I can hold my own now.

 

[JimD]

Our barrel doesn't heat up with a PCP like a powder burner does. Particularly a thin barrel center fire can get too hot to touch. That expands the barrel and it thus not unexpected that a centerfire may shoot differently with a ambient temperature barrel than it does with a "too hot to touch" barrel. My 30-06 is OK for about 3 shots close together which is all I should ever need to shoot it.

But I believe the complex vibratory effects of firing our PCPs are not at all insignificant. This seems to me to be the best explanation of why different pellets shoot so differently. The pressure pulse is much milder since the pressures are so different (less than 3000 for a PCP versus 60.000 or more for a centerfire). If the first shot point of impact is different from a PCP I would think it is a different vibratory response. Possibly because a gun changed temperature and the parts are not aligned exactly the same as they will be in a few shots. I did not see it in my tests of my guns but I think it is still a good idea to test to be sure. I don't think it is at all impossible for a gun to react differently. But I agree that PCPs are less likely to have significant effects than powder burners.

 

[bustachip]

My springers are all lubed very lightly with krytox, and I mean very lightly, a smidge smeared about.
I really think it's more about me than the rifle, if I've been shooting every day and have my hold, breathing, head placement behind the scope..etc. I have, and can be dead on from time to time with the first shots. On the other hand if I haven't shot for a long while, the first shots are usually low and left.
But after I shoot, say, 10 to 15 pellets it comes back to center. Each of my 3 under levers have a different personality so to speak, so I have to spend time to familiarize myself with the one I currently shooting.
My new prosport with it's factory piston seal seems to take more warmup than my 97K with it's O-ring seal, less rubber contact with the compression tube probably.
That's been my experience shooting springers, yours may be completely different. But they can be extremely accurate once you find your groove and pellet combo.

Also nced has done several temperature tests with his 95/R9 from extreme cold (freezing) to really hot, and he finds very little POI shifts with the first shot in his rifles lubed with krytox. He was the "one" that got me interested in O-ring piston seals and lubing with Krytox in the first place. There should be days of reading of his findings on the internet. My 02, it's worth what you paid for it..lol.

 

[Hateful McNasty]

My springers are all lubed very lightly with krytox, and I mean very lightly, a smidge smeared about.
I really think it's more about me than the rifle, if I've been shooting every day and have my hold, breathing, head placement behind the scope..etc. I have, and can be dead on from time to time with the first shots. On the other hand if I haven't shot for a long while, the first shots are usually low and left.
But after I shoot, say, 10 to 15 pellets it comes back to center. Each of my 3 under levers have a different personality so to speak, so I have to spend time to familiarize myself with the one I currently shooting.
My new prosport with it's factory piston seal seems to take more warmup than my 97K with it's O-ring seal, less rubber contact with the compression tube probably.
That's been my experience shooting springers, yours may be completely different. But they can be extremely accurate once you find your groove and pellet combo.

Also nced has done several temperature tests with his 95/R9 from extreme cold (freezing) to really hot, and he finds very little POI shifts with the first shot in his rifles lubed with krytox. He was the "one" that got me interested in O-ring piston seals and lubing with Krytox in the first place. There should be days of reading of his findings on the internet. My 02, it's worth what you paid for it..lol.

Well I posted above it seemed krytox I had that first shot bad most with it .. I did 2 tunes with it and never went with it again. . also with the high shot count I shoot I had to go back and add extra like it would loose it's effectiveness or ware off or something .. it worked great while it lasted I guess. Ijdk. Not impressed to rebuy again I guess in the end result . Lol

 

[Hateful McNasty]

Awesome for irons, you must still have eagle eyes..lol. I got into the airguns later and had to learn to shoot a scope with glasses, but I can hold my own now.

I use to be that hawk eyed rock steady 20 year old, lol... Also never been a scope guy on any gun ...

 

[A.G.R]

Hmmm. Idk.

As is "drop in" but set I hover around 835+850fps with cp-hp.177. now unset they can be hot at first till settled like 920+ , but eventually will settle in about 850 or so .. at least for me anyway.. I been well pleased with arh stuff and really never give the others much thought ..

Edit
Another quick 5 @ 50y ,irons, cp-hp a few min ago. I could say consistent?

View attachment 419448

I can tell you this, the r9 / HW95 platform is snappy after 12 ft lbs no matter how you slice the bologna

No free lunch in a 26 mm tube @85 mm stroke
Short stroking will tame it like a baby like the UK counterparts do

Lightening the piston as well

FAC POWER it’s gonna be a snappy direct reward feel

 

[bustachip]

Well I posted above it seemed krytox I had that first shot bad most with it .. I did 2 tunes with it and never went with it again. . also with the high shot count I shoot I had to go back and add extra like it would loose it's effectiveness or ware off or something .. it worked great while it lasted I guess. Ijdk. Not impressed to rebuy again I guess in the end result . Lol

IDK why you got bad results with it? Maybe factory piston seal or overlubed, head scratcher
for sure.

 

[JDGriz]

Tuned unregulated PCPs can have low-velocity first shots because of valve stiction and weaker first hammer strikes (for example due to bad lubrication); not-tuned or regulated PCPs can get around this by always hitting the valve stem hard enough to always bottom out the valve travel distance, or always open the valve "more than enough".

 

[Hateful McNasty]

IDK why you got bad results with it? Maybe factory piston seal or overlubed, head scratcher
for sure.

More like not impressed overall vs anything else. Not like a spring lasted any more or less shots with it .lol. Just another fact or myth air gun thing I guess ...

Well I was able to post I use krytox in my gun at the time ..

 

[Hateful McNasty]

I can tell you this, the r9 / HW95 platform is snappy after 12 ft lbs no matter how you slice the bologna

No free lunch in a 26 mm tube @85 mm stroke
Short stroking will tame it like a baby like the UK counterparts do

Lightening the piston as well

FAC POWER it’s gonna be a snappy direct reward feel

I guess every action has a equal and opposite reaction. Uk power here? No thanks . Shooting past 50y that don't seem too fun ...

 

[Mycapt65]

My springers are all lubed very lightly with krytox, and I mean very lightly, a smidge smeared about.
I really think it's more about me than the rifle, if I've been shooting every day and have my hold, breathing, head placement behind the scope..etc. I have, and can be dead on from time to time with the first shots. On the other hand if I haven't shot for a long while, the first shots are usually low and left.
But after I shoot, say, 10 to 15 pellets it comes back to center. Each of my 3 under levers have a different personality so to speak, so I have to spend time to familiarize myself with the one I currently shooting.
My new prosport with it's factory piston seal seems to take more warmup than my 97K with it's O-ring seal, less rubber contact with the compression tube probably.
That's been my experience shooting springers, yours may be completely different. But they can be extremely accurate once you find your groove and pellet combo.

Also nced has done several temperature tests with his 95/R9 from extreme cold (freezing) to really hot, and he finds very little POI shifts with the first shot in his rifles lubed with krytox. He was the "one" that got me interested in O-ring piston seals and lubing with Krytox in the first place. There should be days of reading of his findings on the internet. My 02, it's worth what you paid for it..lol.

O ring piston seals have less thermal dimensional change than tradition Weihrauch piston seals. That's a big advantage. It's a common situation for Weihrauchs PO I to slowly wander during long sessions. The piston seal is basically a full width cup seal that has plenty of surface area to expand over time from compression heat. That changes the drag> shot cycle > harmonics and ultimately the POI. It worse when using them in hot weather when the receiver can't radiate the heat well.

Last summer I was pulling my hair out trying to get my guns to shoot consistently for more than a hundred or two shots during abnormally hot sunny weather. After a couple hundred shots the velocity would tank, ES double and groups would fall apart. If I didn't have a chronograph I might have thought the scopes were tanking. Never got it fixed. A fine man from the UK explained to me what I just explained above about the seals thermal changes. Eventually when I get my shop set up I'm gonna design a new piston sealing system that will be less affected by temperature changes.

As to the original post I don't think cold bore accuracy issues on airguns has anything to do with barrel temperatures. I believe it has more to do with minor changes in harmonics from unsettled components.

 

[bustachip]

O ring piston seals have less thermal dimensional change than tradition Weihrauch piston seals. That's a big advantage. It's a common situation for Weihrauchs PO I to slowly wander during long sessions. The piston seal is basically a full width cup seal that has plenty of surface area to expand over time from compression heat. That changes the drag> shot cycle > harmonics and ultimately the POI. It worse when using them in hot weather when the receiver can't radiate the heat well.

Last summer I was pulling my hair out trying to get my guns to shoot consistently for more than a hundred or two shots during abnormally hot sunny weather. After a couple hundred shots the velocity would tank, ES double and groups would fall apart. If I didn't have a chronograph I might have thought the scopes were tanking. Never got it fixed. A fine man from the UK explained to me what I just explained above about the seals thermal changes. Eventually when I get my shop set up I'm gonna design a new piston sealing system that will be less affected by temperature changes.

As to the original post I don't think cold bore accuracy issues on airguns has anything to do with barrel temperatures. I believe it has more to do with minor changes in harmonics from unsettled components.

So far my prosport is shooting consistent with it's factory seal, which is similar to a O-ring seal but has more contact area than a small cross section O-ring. But yes, I had the same problems with my 97K with the factory seal, it was all over the place. The O-ring piston seal conversion made a big difference.

 

[Hateful McNasty]

So far my prosport is shooting consistent with it's factory seal, which is similar to a O-ring seal but has more contact area than a small cross section O-ring. But yes, I had the same problems with my 97K with the factory seal, it was all over the place. The O-ring piston seal conversion made a big difference.

That hw factory installed seal don't hold much confidence.. most undersized I guess so they can easy cram in the tube with out snagging the cutouts razor blades..lol

 

[bustachip]

That hw factory installed seal don't hold much confidence.. most undersized I guess so they can easy cram in the tube with out snagging the cutouts razor blades..lol

I hear the new style is better, I had the old style thin lip parachute seal.

 

[Mycapt65]

I hear the new style is better, I had the old style thin lip parachute seal.

There is no "New Style" Weihrauch seal. I've tuned lots of original old guns and new guns. I'm talking about Weihrauchs. Weihrauch has flip flopped between the thick and thin lipped seals over the years. Almost all of the new guns I've gotten since probably 2019 had the thin lipped seal. I think it's simply a supplier issue.

Theoretically the thin lipped should be less susceptible to temperature expansion. There's a time and a place for them. Parachute seals are good at sealing out of round or tapered tube's. The price is the additional drag of a ballooning seal.

My preferred seal is the Vortek cupped seal. They more durable than factory seals and make more power than parachute designs. The drawback is temperature expansion changes their drag.

Non of this matters to a casual airgunner. Most people don't shoot long enough sessions to notice these various design flaws. I think part of AA success in FT is there seal design suffers less thermal expansion during the course of competition. Traditionally sealed Weihrauchs will suffer wandering POI until there's a better design.

Before anyone jumps down my throat for picking on Weihrauch design. I'll just reiterate that the levels of POI wander I'm talking about most people won't experience. I'm splitting hairs here.

 

[Hateful McNasty]

I hear the new style is better, I had the old style thin lip parachute seal.

I used a few different but the last 2 been the arh hornet seal ..

 

[bustachip]

There is no "New Style" Weihrauch seal. I've tuned lots of original old guns and new guns. I'm talking about Weihrauchs. Weihrauch has flip flopped between the thick and thin lipped seals over the years. Almost all of the new guns I've gotten since probably 2019 had the thin lipped seal. I think it's simply a supplier issue.

Theoretically the thin lipped should be less susceptible to temperature expansion. There's a time and a place for them. Parachute seals are good at sealing out of round or tapered tube's. The price is the additional drag of a ballooning seal.

My preferred seal is the Vortek cupped seal. They more durable than factory seals and make more power than parachute designs. The drawback is temperature expansion changes their drag.

Non of this matters to a casual airgunner. Most people don't shoot long enough sessions to notice these various design flaws. I think part of AA success in FT is there seal design suffers less thermal expansion during the course of competition. Traditionally sealed Weihrauchs will suffer wandering POI until there's a better design.

Before anyone jumps down my throat for picking on Weihrauch design. I'll just reiterate that the levels of POI wander I'm talking about most people won't experience. I'm splitting hairs here.

Yes, I was talking about the thick lip, which I thought was newer design, compared to the older thin lipped seal. I replaced my 97 and 77 with O-ring seals, although it is a snappier shot cycle, it's worth the trade off.

 

[bustachip]

I used a few different but the last 2 been the arh hornet seal ..

I also tried a hornet seal for awhile before switching to the O-ring seal.

 

[Mycapt65]

I also tried a hornet seal for awhile before switching to the O-ring seal.

The Hornet seal iirc is a cupped seal similar to the Vortek seal. The Hornet seal requires sizing in order to make proper power. I've used all the JM Weihrauch piston seals at one time or another but I may have the name of the styles incorrect. IMO the Vortek seals under most conditions are the best replacement seal for Weihrauchs. They size themselves with some use and typically make more power than parachute styles. It's a good combination of ease of installation, durability and output. Obviously not perfect but that falls more on Weihrauchs full span piston seal concept than anything else.