Pressure buildup dump valve for springers?

[K.O.]

me I always wondered about giving it a big Shot of CO² into the piston chamber right as the piston is released...

wondered what temps it would hit since it expands much more than air with rising temp... would it just slow the piston...

would cooling in the barrel negate any gains...

just one of those things have been curious about for a long time... sounds silly tho... a CO² springer..  

https://www.catalinacylinders.com/faqs/dangers-of-heat-exposure-to-co2-cylinders/

[Jim-in-UK]

I don't know about all the scientific stuff but when I've accidentally dry fired my Weihrauchs it sounds like a gunshot. I assume that's detonation from a very rapid increase of pressure. My guess is the detonation reverses the piston direction violently before it reaches the end of the compression tube. I also believe it reverses much harder and further than normal piston bounce.

I've had factory Weihrauch seals ruptured and useless by a single dry fire. I've also noticed premature spring breakage in guns that have been dry fired.

Interestingly enough it's supposedly ok to dry fire a Hw45. I have one and have done it several times. It too detonates but it has a tougher Teflon piston seal. Not sure why the Hw45 spring handles the dry fire better than their rifles.

Dry firing has been a topic many times and people have varying opinions. I can say I've absolutely damaged seals and springs in Weihrauch rifles. Ymmv with other guns.

I did not get any obvious detonations with my dry fire tests, possibly because our springers have less spring potential energy, but a deliberate detonation in the same poor little Anschutz 335 produced massive piston bounce, and it is not unknown for detonations to re-cock springers. The peak temperature with 'FAC' springers may well be enough to cause damage to seals, and the violent piston bounce will do mainsprings no good at all.

It would be useful to get a chemist on board to explain the conditions that can cause detonation.

[Bayman]

I don't know about all the scientific stuff but when I've accidentally dry fired my Weihrauchs it sounds like a gunshot. I assume that's detonation from a very rapid increase of pressure. My guess is the detonation reverses the piston direction violently before it reaches the end of the compression tube. I also believe it reverses much harder and further than normal piston bounce.

I've had factory Weihrauch seals ruptured and useless by a single dry fire. I've also noticed premature spring breakage in guns that have been dry fired.

Interestingly enough it's supposedly ok to dry fire a Hw45. I have one and have done it several times. It too detonates but it has a tougher Teflon piston seal. Not sure why the Hw45 spring handles the dry fire better than their rifles.

Dry firing has been a topic many times and people have varying opinions. I can say I've absolutely damaged seals and springs in Weihrauch rifles. Ymmv with other guns.

I did not get any obvious detonations with my dry fire tests, possibly because our springers have less spring potential energy, but a deliberate detonation in the same poor little Anschutz 335 produced massive piston bounce, and it is not unknown for detonations to re-cock springers. The peak temperature with 'FAC' springers may well be enough to cause damage to seals, and the violent piston bounce will do mainsprings no good at all.

It would be useful to get a chemist on board to explain the conditions that can cause detonation.

I'm not sure a chemist is needed. As an automobile mechanic detonation is a common problem. Detonation is an unplanned violent explosion of combustible materials caused by heat. In cars it can be from any combination of causes. It can be caused by excessive cylinder pressure like a high compression engine running on low octane fuel. Here the heat from the cylinder pressure exceeds  the fuels ignition point. The compression ignites the fuel before the plug sparks. It can also be caused by rapid cylinder pressure build up. Running too much spark advance lights the fuel mixture too far into the compression stroke and the compression stroke is now try to compress an already expanding burning mixture. That creates very high cylinder pressure that can light pockets of yet unburnt mixture. That's the pinging you hear. Along with that glowing hot spots from irregularities in the combustion chamber can light the mixture early. Irregularities can be large carbon deposits burned valve heads, sharp machined edges on pistons and heads and the edges of head gaskets.

Bottom line all the detonation involves extreme pressures, heat, combustible mixture and an unplanned, uncontrollable explosion. There's not a lot of chemistry involved. It's mostly mechanical.

[subscriber]

Bayman,

Surely dry firing a springer is like running an engine with the spark plug removed.  The resultant compression pressure should be lower than with the plug or pellet installed, not higher. 

Now, in a dry fire I can see that the air at the periphery of the compression cylinder would have to squish very rapidly towards the transfer port.  The airflow velocity through the TP would also be very high - to the point of choking the flow, probably.  Possibly either or both of those air flow conditions might raise the air temperature drastically via molecular friction.  Else dry firing should be less likely to diesel than with a oversize pellet jammed in the breech.

I am not suggesting your observation is incorrect.  I just can't wrap my head around the mechanism.  Perhaps the air in the annular groove of (some) Weihrauch piston seals is trapped and super compressed during an un-cushioned dry fire, to the point where the seal material itself is the fuel for a dieseling event.

[Bayman]

Bayman,

Surely dry firing a springer is like running an engine with the spark plug removed.  The resultant compression pressure should be lower than with the plug or pellet installed, not higher. 

Now, in a dry fire I can see that the air at the periphery of the compression cylinder would have to squish very rapidly towards the transfer port.  The airflow velocity through the TP would also be very high - to the point of choking the flow, probably.  Possibly either or both of those air flow conditions might raise the air temperature drastically via molecular friction.  Else dry firing should be less likely to diesel than with a oversize pellet jammed in the breech.

I am not suggesting your observation is incorrect.  I just can't wrap my head around the mechanism.  Perhaps the air in the annular groove of (some) Weihrauch piston seals is trapped and super compressed during an un-cushioned dry fire, to the point where the seal material itself is the fuel for a dieseling event.

The empty spark plug hole is a bad example because the build up of pressure in a combustion engine cylinder is very slow compared to a spring piston gun. The piston is attached to a rotating crank by a connecting rod. The design inherently decelerates the piston at the top and bottom the stroke. I do understand your logic. Without a cork in the hole pressure shouldn't build up at all.

It may not be the amount of pressure but rather the rate of pressure build up. When you dry fire a petroleum based lubricated gun, something explodes. It's quite evident by the loud crack and the smoke that comes out of the barrel. The transfer port may be just enough of restriction that it creates a super rapid build up of pressure. Albeit possibly less pressure overall.

I believe it's the rate of pressure build up that causes heat. Pump up a bicycle tire slowly and the pump cylinder never gets hot. Now pump up the tire quickly and you can almost burn your hand on the pump cylinder. Both case the there's little back pressure from the tire.

Perhaps it's the heat from that super rapid pressure build up ignites every petroleum particle in the compression chamber. Or perhaps the air passing through the port so rapidly creates a super heated gas jet which in turn lights the petroleum vapor. I can't tell you exactly how it happens. I can tell you something explodes in there. If you don't believe me dry fire one of your Weihrauchs and prove me wrong. You'll likely be replacing the OE seal after a time or two. Ask me how I know 

The only other possibility I can think of is the loud crack may be the air exiting at supersonic speeds. I'm not even sure if air by itself could cause a sonic crack. I also don't know how that would account for the smoke and ruptured piston seals.

Sometimes knowing why something happens isn't as important as knowing it does. It's still interesting to ponder.

Be well my friend
Ron

[subscriber]

If you don't believe me dry fire one of your Weihrauchs and prove me wrong.

My mechanical sympathy won't allow me to do that.  It is like deliberately jumping off a second story roof, just to see what it is like.

The only springer I have dry fired deliberately is my HW 45 (P1), as this is how the Teflon piston seal is form fitted to the compression cylinder.

The idea that the unobstructed airflow through the TP is supersonic when dry firing a springer seems reasonable.  If so, airflow from the muzzle might also be supersonic.  In which case the cracking noise has at least one explanation.

I think that the airflow is more complicated that a simple ratio of areas, piston to TP, but if anyone knows the velocity of a springer piston when dry fired, perhaps that might be an interesting thought experiment.  From memory, (based on a PA educational video) peak piston speed of a normal firing event is 50 to 100 FPS.  But, then initial airflow through the TP is zero, until the pellet starts moving.  Then airflow follows the pellet, so can't be any faster, until the pellet uncorks from the muzzle.

Anyway, ignoring air compression and acceleration during expansion, just looking at the ratio of areas of a 25 mm diameter piston and a 4.5 mm pellet, if the piston moves at 100 FPS, the air travelling through a 4.5 mm "pipe" needs to move at  3080 FPS.  Now, even accounting for the speed of sound being higher when air is above atmospheric pressure, that air probably can't flow that fast due to friction losses and the TP acting as a choke; but it seems that dry firing a springer reasonably could cause air to leave the muzzle at over 1150 FPS.  So, it would crack loudly.

[Bayman]

If you don't believe me dry fire one of your Weihrauchs and prove me wrong.

My mechanical sympathy won't allow me to do that.  It is like deliberately jumping off a second story roof, just to see what it is like.

The only springer I have dry fired deliberately is my HW 45 (P1), as this is how the Teflon piston seal is form fitted to the compression cylinder.

The idea that the unobstructed airflow through the TP is supersonic when dry firing a springer seems reasonable.  If so, airflow from the muzzle might also be supersonic.  In which case the cracking noise has at least one explanation.

I think that the airflow is more complicated that a simple ratio of areas, piston to TP, but if anyone knows the velocity of a springer piston when dry fired, perhaps that might be an interesting thought experiment.  From memory, (based on a PA educational video) peak piston speed of a normal firing event is 50 to 100 FPS.  But, then initial airflow through the TP is zero, until the pellet starts moving.  Then airflow follows the pellet, so can't be any faster, until the pellet uncorks from the muzzle.

Anyway, ignoring air compression and acceleration during expansion, just looking at the ratio of areas of a 25 mm diameter piston and a 4.5 mm pellet, if the piston moves at 100 FPS, the air travelling through a 4.5 mm "pipe" needs to move at  3080 FPS.  Now, even accounting for the speed of sound being higher when air is above atmospheric pressure, that air probably can't flow that fast due to friction losses and the TP acting as a choke; but it seems that dry firing a springer reasonably could cause air to leave the muzzle at over 1150 FPS.  So, it would crack loudly.

You'll have airflow through the tp long before before the pellet moves. This is not hydraulics. Air is compressible so air has to move through the transfer port to behind the pellet to build enough pressure to pop it out.

Perhaps it is a sonic crack but would it have to rearward shock wave? That would explain the ruptured seals and the piston reversing. But what about the smoke and the burnt piston seals?

[subscriber]

Of course air has to move into the space behind the pellet, but that mass flow, while seeing high acceleration does not see high velocity before the pellet moves, because the bulk of that air does not move very far.   

That said, before the pellet moves, the air already in contact with it does not move.  The air one mm into the TP moves very little in order to build pressure.  The air upstream of the TP follows the piston, until it is squished into the TP.  That slows the air flow down, but increases its pressure (so the molecules move faster in random fashion).

Air behind the pellet, before the pellet moves, is more like the spring in a springer when you cock it.  The spring in contact with the endcap does not move anywhere, while the spring in contact with piston has to move to increase the force in the system.  So, some of it moves to establish the new cocked or pressurized state. 

That motion is insignificant compared to what happens as soon as the pellet pops the breech cone.  It is like the difference between parking your car in the garage, VS accelerating on a 1/4 mile drag strip. 

[subscriber]

While an R1 may have a "long" TP, the fixed barrel TX200 Jim used for his testing does not.  That is what I had in mind, when stating that flow in the TP before the pellet moves is negligible.  Practically zero.  Like parking a car in a garage...

[Jim-in-UK]

Bayman; thank you for the detailed information on the IC engine, all of which I am fairly familiar with. The reason I suggested a chemist might be of help is that the cylinders of springers do not contain a fine mist of petrol or diesel droplets, but a little grease of some kind, usually mineral oil based, lithium soap thickened, and with molybdenum disulphide, or a silicone oil base with various additives and PTFE.

In the case of the mineral oil base grease, we can take a stab at the flash point and autoignition temperatures, but need to know under what conditions the flame front propagation exceeds Mach 1, the point at which a diesel becomes a detonation, in my understanding. In the case of silicone oil base greases, and any lubricant with a brand name ending in 'ox', I would like to know what happens to the considerable amount of oxygen they contain when the cylinder temperature passes the point at which they break down (400C). Both are firmly in the territory of the chemist.

[Bayman]

Bayman; thank you for the detailed information on the IC engine, all of which I am fairly familiar with. The reason I suggested a chemist might be of help is that the cylinders of springers do not contain a fine mist of petrol or diesel droplets, but a little grease of some kind, usually mineral oil based, lithium soap thickened, and with molybdenum disulphide, or a silicone oil base with various additives and PTFE.

In the case of the mineral oil base grease, we can take a stab at the flash point and autoignition temperatures, but need to know under what conditions the flame front propagation exceeds Mach 1, the point at which a diesel becomes a detonation, in my understanding. In the case of silicone oil base greases, and any lubricant with a brand name ending in 'ox', I would like to know what happens to the considerable amount of oxygen they contain when the cylinder temperature passes the point at which they break down (400C). Both are firmly in the territory of the chemist.

I'm sorry I didn't understand the we were talking about different lubricant bases. Yes of course we'd need a chemist then. Interesting tid bit I've had guns clearly detonate with just a drop too much RWS silicone chamber oil. I found this out when I was brand new into spring guns. A newbie mistake. I never use the stuff any more. I've also had guns that were thoroughly cleaned smoke with Krytox when I got careless with the application. I'm not sure it's really smoke from burning or its vaporization. It's not supposed to burn. I've never dry fired a Krytox gun and I'm not willing to try it.

[Bayman]

But, then initial airflow through the TP is zero, until the pellet starts moving.  Then airflow follows the pellet, so can't be any faster, until the pellet uncorks from the muzzle.

Subs, This is what I was addressing. You said zero. Not very little or insignificant. You'd be surprised how much air gets stuffed quickly into that small space behind the pellet and in the TP before the pellet moving. Air is very compressible.

Also I'm not sure the second part of the statement is correct depending if your talking about the airflow velocity directly behind the pellet or the TP. The airflow velocity in the TP is definitely moving faster than the pellet because it's a smaller pipe filling a bigger pipe.

[subscriber]

Ron

You are correct that the flow velocity in the TP needs to be the inverse of the ratio of flow areas, compared to bore size, once the pellet is accelerating down the barrel.

I want to give you the first part of the statement, but when the pellet is sitting against the breech cone, technically there is no flow through the TP.  There is flow into the TP with the pressure increasing in the TP as the piston moves closer to the end of its stroke. 

For there to be flow through the TP the pressure at the TP inlet and outlet have to be different.   Pressure differential is what drives flow, not just high pressure.  Once the pellet pops the leade and starts moving, the pressure differential is not just between the rear of the TP and the front of the TP, but between the rear of the TP and the front of the pellet.  So, there is a massive pressure differential that drives flow once the pellet cannot hold back the force building on its skirt.

Technically, linguistically and legally, you are correct that there must be more molecules of air in the TP for pressure to build, before the pellet moves.  How did those extra molecules get into the TP?  They flowed there because for an instant there was a pressure differential across the TP, even before the pellet moved.  That process slowed down to a near stop, like when you fill a PCP tank from a pressure source that is at your target pressure.

So, pedantic perhaps, but I made a distinction between air flowing into the TP space, and coming out the front end.  Flowing into, VS through.

The TP length on an R1, for example is more that 3/4".  Whereas on a TX200 it is perhaps half of that.  So, since the results we are talking about were obtained TX200, I claim that the pressure differential across the TX200 TP is not very large because it is so short and has such a small volume that the filling to pressure is near instant.

Further, the TP restriction does not matter, until the pellet pops loose from the breech.  And yes, there is a ratio of air flow speeds, that can be predicted from bore and TP flow areas.  But once the pellet stars moving, the air directly behind the pellet flows at the same speed as the pellet moves - unless air leaks past the pellet. 

So, I am going to paraphrase you statement as advice to me:  "Be careful of making absolute statements that apply only under specific conditions.  Be clear about the exact conditions that apply."

[Bayman]

Ron

You are correct that the flow velocity in the TP needs to be the inverse of the ratio of flow areas, compared to bore size, once the pellet is accelerating down the barrel.

I want to give you the first part of the statement, but when the pellet is sitting against the breech cone, technically there is no flow through the TP.  There is flow into the TP with the pressure increasing in the TP as the piston moves closer to the end of its stroke. 

For there to be flow through the TP the pressure at the TP inlet and outlet have to be different.   Pressure differential is what drives flow, not just high pressure.  Once the pellet pops the leade and starts moving, the pressure differential is not just between the rear of the TP and the front of the TP, but between the rear of the TP and the front of the pellet.  So, there is a massive pressure differential that drives flow once the pellet cannot hold back the force building on its skirt.

Technically, linguistically and legally, you are correct that there must be more molecules of air in the TP for pressure to build, before the pellet moves.  How did those extra molecules get into the TP?  They flowed there because for an instant there was a pressure differential across the TP, even before the pellet moved.  That process slowed down to a near stop, like when you fill a PCP tank from a pressure source that is at your target pressure.

So, pedantic perhaps, but I made a distinction between air flowing into the TP space, and coming out the front end.  Flowing into, VS through.

The TP length on an R1, for example is more that 3/4".  Whereas on a TX200 it is perhaps half of that.  So, since the results we are talking about were obtained TX200, I claim that the pressure differential across the TX200 TP is not very large because it is so short and has such a small volume that the filling to pressure is near instant.

Further, the TP restriction does not matter, until the pellet pops loose from the breech.  And yes, there is a ratio of air flow speeds, that can be predicted from bore and TP flow areas.  But once the pellet stars moving, the air directly behind the pellet flows at the same speed as the pellet moves - unless air leaks past the pellet. 

So, I am going to paraphrase you statement as advice to me:  "Be careful of making absolute statements that apply only under specific conditions.  Be clear about the exact conditions that apply."

Peter I like you, your a great, smart man and I'm not trying to argue or de-edify you in any way. Air does flow through the transfer port before the pellet moves. There's volume within the pellet itself and the area within the breech seal. So there's automatically pressure differential between both ends of transfer port. The volume is small but you'd be surprised how much air might get crammed in there before the pellet pops. Especially a tight one with a deep skirt well.

This is neither here nor there and don't see the need to dwell on this minutiae any longer. As there are others that like to pick fights with us (or me at least) that already drain the enjoyment we get from our discussions on the forum. I enjoy our discussions and would like to move on. Perhaps if the crack is sonic air where does the smoke and piston seal damage come from?

Factory Weihrauch Piston seals often erode or burn through from excessive dieseling but usually rupture cleanly on dry fire. I would think that has to do with an explosion of sorts. Certainly excessive pressure.

[subscriber]

Ron,

It is a matter of perspective.  And scale. Before one zooms in to find a street address, you need to confirm that you are in the right city.  In other words, details matter, but only if the big picture is correct.  You are correct:  If one wants to be exact, then all details matter.   

I am aware of the pellet skirt volume, but that is miniscule in my opinion, compared to the TP volume, and the space ahead of the piston when it almost reaches the endwall of the cylinder in normal firing.   But you are correct to acknowledge that before the pellet moves, the space on the downstream side of the TP is in fact not zero.  I ignore it, because I consider it insignificant, compared to the rest of the system.  Contrast that with deep seating a pellet into the barrel, to potentially double the TP volume.  Deep seating also gets rid of the pellet's function as pressure release valve, that delays acceleration until the pressure has built up as designed.

Speculation:
I think that when you dry fire a potent springer the air that is compressed near the ID of the cylinder endwall has to accelerate very drastically towards the TP.   This behaves like the deliberate squish zone in the combustion chamber of an engine. 

In a dry fired springer, that squish zone air moves so aggressively, that is scrubs off grease from the piston face (yes, we don't want it there, but sometimes it is a factory bonus).   

Jim touched on a good point when he said that a diesel engine runs on oil mist, and that grease is not mist.  Well, when you have such an aggressive "wind" blowing parallel to the piston face, it blow off any grease that may have migrated there, and effectively breaks it into smaller chunks that include mist.  The small chunks have a large surface area to volume ratio and heat up rapidly.  Even if the grease is not combustible, the flow atomization and heating produce the smoke you observe.

If the grease has a combustible components they may burn.  Actual combustion is likely if there is a burnt smell; else the vapor may just look like "smoke".

It is possible that the hot air is actually superheating the plastic piston seal and cause that to smoke.  Now, the piston seal normally sees hot air and survives just fine.   In terms of heat exchange, there is a difference between containing hot gas and having it flow over a small region:  A cut in a piston seal will cause it to leak at the cut.  That concentrated mass flow will tend to cause local overheating of the seal.  This may result in the seal looking melted, or eroded.  The latter means the seal was vaporized and / or oxidized.

So, I am suggesting that dry firing changes the way hot air flows over the piston face; in a way that is prone to local overheating.  With or without grease present.

[rsterne]

If you gentlemen are saying that the pressures and temperatures are higher in a springer when dry-fired, than they are with a pellet in the breech, I would respectfully disagree.... It makes no sense that providing a path for the air to escape can increase the pressure....

Bob

[subscriber]

If you gentlemen are saying that the pressures and temperatures are higher in a springer when dry-fired, than they are with a pellet in the breech, I would respectfully disagree.... It makes no sense that providing a path for the air to escape can increase the pressure....

Bob

Bob, I agree with you. 

I am trying to find a way to explain the observations about loud dieseling when a springer is dry fired.   Bulk air compression has to be lower because there is a hole in the system.  The speed of the air from the muzzle may be supersonic, and be misunderstood as dieseling.  Or, there may be some sort of localized hotspot, rather than bulk heating.

The flip side is that maximum pressure and temperature should occur, if the pellet is jammed or glued into the breech.  In other words an immovable non-leaky plug.

[Bayman]

If you gentlemen are saying that the pressures and temperatures are higher in a springer when dry-fired, than they are with a pellet in the breech, I would respectfully disagree.... It makes no sense that providing a path for the air to escape can increase the pressure....

Bob

I'm not saying that the pressure is higher mechanically during a dry fire. I'm saying that there's an explosion that  causes smoke and ruptured seals. It's excessive pressure from the detonation (rapid explosion) that ruptures the piston seals.

Dieseling is an entirely different than detonation. Dieseling is more of a slower controlled burn of combustible materials. Dieseling doesn't rupture seals. Some dieseling is normal and not damaging. Excessive dieseling melts holes in piston seals. It's a different condition and different failure.

I had a RX1 (Hw90) that had a star shaped channeling towards the TP and the piston seal had a corresponding pattern burnt or eroded out of it. This was likely the result of the Theoben ram being overcharged. Which it was when I got it. The heat created by the compressed fast passing air either melted or eroded the corresponding pattern in the seal. Burned out seals was a common issue with these guns during the period my gun was made. Rapid air flow through a restriction creates heat by itself. No back pressure is needed. In fact the lack of back pressure during a dry fire is probably what creates the heat that causes the detonation.

I stand by my statements. During a dry fire detonation definitely occurs. The sound, smell, smoke an blown out piston seals all confirm it. Also as Jim mentioned guns have been known to rebound so harshly they recock themselves. Something pushed the piston back harder than any normal function. Spring life is greatly shortened in a dry fired gun because of violent bounce back. There's just too much evidence that points to detonation. 
Remember dieseling from pressure and detonation from heat are too different things. As embarrassing as it is I've personally had both conditions and their corresponding failures, so I know what condition caused what failure. What I can't say for sure is what causes the detonation on a dry fire. I believe it has something to do with the rapid rate of pressure increase and or the heat created by the shear velocity of the unrestrained air.

Ron

[subscriber]

I had a RX1 (Hw90) that had a star shaped channeling towards the TP and the piston seal had a corresponding pattern burnt or eroded out of it. This was likely the result of the Theoben ram being overcharged. Which it was when I got it. The heat created by the compressed fast passing air either melted or eroded the corresponding pattern in the seal.

Ron,

If your used seal looked like the image below, the channels were molded into the seal during manufacturing:

https://www.airgunspares.com/th101034theobenevopistonwasherold.html



It would be much cheaper to mold channels into the piston seal, than to emboss or cut them into the steel cylinder "head". 

Here is the patent diagram for such a seal with air flow channels:  https://patentimages.storage.googleapis.com/2c/5b/2c/bd284b28490579/US4771758.pdf

[Bayman]

I had a RX1 (Hw90) that had a star shaped channeling towards the TP and the piston seal had a corresponding pattern burnt or eroded out of it. This was likely the result of the Theoben ram being overcharged. Which it was when I got it. The heat created by the compressed fast passing air either melted or eroded the corresponding pattern in the seal.

Ron,

If your used seal looked like the image below, the channels were molded into the seal during manufacturing:

https://www.airgunspares.com/th101034theobenevopistonwasherold.html



It would be much cheaper to mold channels into the piston seal, than to emboss or cut them into the steel cylinder "head". 

Here is the patent diagram for such a seal with air flow channels:  https://patentimages.storage.googleapis.com/2c/5b/2c/bd284b28490579/US4771758.pdf

No the corresponding pattern was burned away and or eroded by the passing of very hot air. C'mon Peter give me a little credit. I can tell when something is molded that way as opposed to worn or damaged. I know what I'm looking at. If I don't I'll be the first to admit it.

The OE seal when my gun was made was the standard flat faced Weihrauch 30mm parachute piston seal that came on the Hw80 and 35. The seal you posted is for a theoben not the Weihrauch with borrowed Theoben design.

And the star shaped channel was machined into the compression tube end before it was brazed together. If I can find a picture I'll post it.
Regards
Ron