Tuning The Heat's messing with my springers.

[AirShot]

It is called physics....heat causes expansion and materials expand at different rates. Cool does just the opposite, no way around it !!! As a good friend used to say " things just bees that way". Just learn to live with it, each gun/ scope will be a little different.

 

[GoldenStateAIRGUNer]

Think of them like a normally aspirated car engine. The higher you go into the mountains (less air density) the less power it has. Now a turbo charged car isn't affected which would equate to a PCP. There's also a process that occurs in springers

I agree up until the part where you state that turbocharged engines aren't affected by elevation. They are !
A forced induction engine at 14.7 psi (sea level) isn't going to produce the same power at 12 psi ( 6000').

 

[MartyMcFly]

Another observation I found, is the trend for tight fitting plastic guides and Top hats (Usually Delrin) playing havoc at elevated Temp....as the plastic expands due to heat.

It's interesting that the FWB 65 with its regular steel guide rod and steel piston ring, remains relatively unaffected by temp variation...I have also found Leather sealed guns remain immune from temp rise, but with leather we have the other problem of re-lubing inconsistencies to work around...

I don’t think the Delrin guides and top hats are to blame (in most cases). A compression spring’s diameter expands enough when cocked that a tight fit guide will no longer be in contact with the spring until the spring has decompressed. However, Delrin will be a bigger factor if it is used as a piston button or piston ring used to center or reduce metal on metal friction. When it gets hot it will slow things down as the coefficient of fiction for Delrin increases.

That said, humidity might be a significant factor too. I’m sure that compression in a springer is less effective with saturated air vs dry air. Someone on here probably has a graph that shows the ratio of humidity to temperature relationship for compression and my best guess is that the efficiency improvement from higher temperatures is eaten up by the loss to higher humidity. In an FWB300 or 65 it’s likely that it’s power level does not reach the same compression ratio (high heat) where humidity has an increasingly power robbing impact.

Anyways, I’m sure someone who knows the physics well will be around shortly to correct me

-Marty

PS - Edit: Just read that in air compressors, which are not springers but undoubtedly share some of the same physics, the impact of humidity can be considerable. As air is sucked in and compressed the water vapor density increases as does the temperature, then when the compressed air is released or cools the relative humidity of that air increases and it will begin to precipitate. My guess is that in springers the cooling action takes place in the transfer port. It’s very fast and the air is quickly expelled however, you need just a little of the precipitation to occur in the TP in order to cling to the walls and cause increased air flow resistance (effectively shrinking the TP diameter for a split second). Any physics wiz on here that can confirm?

 

[Bear-of-Grayling]

Hey Ron. Welcome to the South. Your mild weather would be a treat for me. Heat index the other day was 115. Humidity about the same. I don’t shoot rifles in this weather. Don’t want the bellies to rust from the sweating. To hot anyway. If I must pull a trigger it’s on a pistol. Stainless one.

 

[Steveoo]

Delrin guides not the problem.....The problem is it don't work like that...because I have proven it time upon time that they can bring issues with temperature..
With guides and Top Hats they are often driven on. While spring expansion at full cock is not nearly as great as once considered...in fact some springs barely opening up at all at full compression, let alone under supposed pre load...
I have measured numerous springs, once thought to expand by 0.5mm in dia. fully cocked, which had not expanded more than 0.2mm...and sometimes less.
An already tight guide with 0.1mm of interference could go up another 0.15mm (if you check temp expansion figures).."that equates a big problem.

One thing I warned many so called Tuners about when employing Delrin, is never to go too tight on tolerances..
It does not need it, as even a sloppy Delrin guide will kill twang much better than a steel one. Not that I'm suggesting going with Sloppy, but these interference fits will see problems.
You correctly highlight even greater potential problems with piston rings, often made to very close tolerance. Some tuners even proud of how tight they have their tolerance....big mistake..

It's interesting that in F1 Motor sport, they never talk in tight tolerance terms.....they talk in correct clearance terms...that's the key ...

As regard the FWB 6ftlb sledge system in 300 and 300 SU models....they will diesel for fun if incorrect lubes get inside, proving they generate ample heat for problems...

 

[Mycapt65]

I'm considering modifying a Weihrauch piston to use a hollow piston seal like a AA TX. This should reduce the total thermal expansion of the seal and hopefully give more consistent performance.

The AA seals are 25mm. Does anyone know of similar design seals in 26 or 30mm?

 

[DesertSilver]

I agree up until the part where you state that turbocharged engines aren't affected by elevation. They are !
A forced induction engine at 14.7 psi (sea level) isn't going to produce the same power at 12 psi ( 6000').

You're forgetting the waste gate which shouldn't open until you reach the boost set point which should be the same as at sea level. I've only had one car with a turbo so I'm not sure on that account. I'm taking about a mechanical waste gate not a electronically controlled one.

 

[MartyMcFly]

Delrin guides not the problem.....The problem is it don't work like that...because I have proven it time upon time that they can bring issues with temperature..
With guides and Top Hats they are often driven on. While spring expansion at full cock is not nearly as great as once considered...in fact some springs barely opening up at all at full compression, let alone under supposed pre load...
I have measured numerous springs, once thought to expand by 0.5mm in dia. fully cocked, which had not expanded more than 0.2mm...and sometimes less.
An already tight guide with 0.1mm of interference could go up another 0.15mm (if you check temp expansion figures).."that equates a big problem.

One thing I warned many so called Tuners about when employing Delrin, is never to go too tight on tolerances..
It does not need it, as even a sloppy Delrin guide will kill twang much better than a steel one. Not that I'm suggesting going with Sloppy, but these interference fits will see problems.
You correctly highlight even greater potential problems with piston rings, often made to very close tolerance. Some tuners even proud of how tight they have their tolerance....big mistake..

It's interesting that in F1 Motor sport, they never talk in tight tolerance terms.....they talk in correct clearance terms...that's the key ...

As regard the FWB 6ftlb sledge system in 300 and 300 SU models....they will diesel for fun if incorrect lubes get inside, proving they generate ample heat for problems...

Steveoo, you are probably right regarding the Delrin thermal expansion in cases where there is no clearance. Out of curiosity, I ran some theoretical numbers on my own setup (hopefully I didn't make any errors). This is for a TX200 comparing a steel to Delrin inner spring guide:

Initial Conditions at 70 degrees:
Stainless Steel Guide OD: 0.5325 inches
Delrin Guide OD: 0.5325 inches
Spring ID: 0.5625 inches

Material Coefficient of Thermal Expansion used:
Stainless Steel Guide 9.4 x 10^-6 in/in F
Delrin Guide 50 x 10^-6 in/in F
Spring 12 x 10^-6 in/in F (I assumed the spring is of cheaper steel than the guide, thus higher CTE).

Final Conditions at 120 degrees (+50 degree swing):
Stainless Steel Guide OD: 0.55426 inches (0.00026 increase)
Delrin Guide OD: 0.55539 inches (0.00138 increase, 5.3x more than steel)
Spring ID: 0.56216 inches (0.00034 decrease)

Clearance at 120 degrees (not accounting for ID expansion due to loaded spring):
Stainless Steel Guide: 0.56216 - 0.55426 = 0.0079 inches
Delrin Guide: 0.56216 - 0.55539 = 0.00677 inches

The spring ID should enlarge by up to 0.006066 inches, so for the Delrin guide there will be at most 0.012836 inches of clearance and for the steel guide there will be 0.013966 inches. BUT keep in mind that in my setup you can easily remove the spring guides. I've not been able to do the same with commercial kits, which implies they are not leaving much room for thermal expansion.

Please note that this is an extreme example and there will always be deviations in theoretical calculation, but its certainly something to keep in mind when tuning for hot weather.

PS. Mistakes are my own - its worth double checking the work when doing your own tune.

-Marty

 

[KWK]

I'm considering modifying a Weihrauch piston to use a hollow piston seal like a AA TX. This should reduce the total thermal expansion of the seal and hopefully give more consistent performance.

The AA seals are 25mm. Does anyone know of similar design seals in 26 or 30mm?

Look at the Custom Air Seals website. There are some possibilities. The diameters are given.

CustomAirSeals - Air Rifle Seals Springs and Spare Parts

Air Rifle Pellet Gun Seals Springs and Spare Parts to suit Gamo, Weihrauch, BSA, Hatsan, Cometa, Norica and Diana. Custom made piston and breech seals to suit any application

www.customairseals.com

 

[billketsugo]

I asked this once but it was more about the sweating. I think moisture is the most likely cause. That gun sweats both inside and out covering every part. And it's a helluva lot. I quit shooting on those sticky wet summer mornings. And I shoot mostly open sights. Must be hell on scopes too.

 

[Mycapt65]

I asked this once but it was more about the sweating. I think moisture is the most likely cause. That gun sweats both inside and out covering every part. And it's a helluva lot. I quit shooting on those sticky wet summer mornings. And I shoot mostly open sights. Must be hell on scopes too.

I agree in part because the moisture probably plays a part in overall power loss. The moisture occupies space in the compression tube where air should be. Plus I did find that the Krytox turned sticky in one gun. I believe the compression either mixed or pushed the moisture into the Krytox. It's probably best to let the guns acclimate more slowly so they don't sweat inside and out.

Still after the humidity burns off later in the day I'm experiencing overall velocity and accuracy issue when shot over a long time. When the guns are put aside for a while to cool down a bit the velocity and accuracy returns. That happens whether it's humid or not. The heat is the common denominator.

Scopes are sealed with nitrogen or I believe argon. There's no moisture in the scope to sweat internally. But they are prone to shifting zeros from temperature and direct sunlight heat. There's a whole thread on it here.

Be well
Ron

 

[scotton]

Mr. Capt65

What Springers are you shooting? What tunes do you have in there?
I'm guessing that there might be some temperature sensitive components in there? (Delrin? temperature sensitive lube?)

I used to tape one of those fish tank thermometer strip on my scope to monitor temperature changes. I don't know how accurate it was and it ultimately peeled off (now I got little lumps to temperature sensitive material glued onto the scope...hmm).

I'm going to purchase an infra red thermometer and track the performance of my TX and my scope. As soon as I get results, I'll post.

Anyone got any recommendation on an infra red handheld thermometer? Is this one from Amazon a good buy?


B07VTPJXH9

They are all basically the same. This is the important thing to know about IR thermometer guns: "With its distance-to-spot ratio of 12:1...". The gun is measuring a cone. For this particular gun, a foot away from the target you are measuring the average temperature of an inch. All this means is that the closer you are to the target, the more accurate the temperature reading will be. And don't fall in love with the laser pointer on the gun, it can be off by a few inches. Just get as close as you can and move the IR gun around a little to get the highest temperature.

 

[Steveoo]

Steveoo, you are probably right regarding the Delrin thermal expansion in cases where there is no clearance. Out of curiosity, I ran some theoretical numbers on my own setup (hopefully I didn't make any errors). This is for a TX200 comparing a steel to Delrin inner spring guide:

Initial Conditions at 70 degrees:
Stainless Steel Guide OD: 0.5325 inches
Delrin Guide OD: 0.5325 inches
Spring ID: 0.5625 inches

Material Coefficient of Thermal Expansion used:
Stainless Steel Guide 9.4 x 10^-6 in/in F
Delrin Guide 50 x 10^-6 in/in F
Spring 12 x 10^-6 in/in F (I assumed the spring is of cheaper steel than the guide, thus higher CTE).

Final Conditions at 120 degrees (+50 degree swing):
Stainless Steel Guide OD: 0.55426 inches (0.00026 increase)
Delrin Guide OD: 0.55539 inches (0.00138 increase, 5.3x more than steel)
Spring ID: 0.56216 inches (0.00034 decrease)

Clearance at 120 degrees (not accounting for ID expansion due to loaded spring):
Stainless Steel Guide: 0.56216 - 0.55426 = 0.0079 inches
Delrin Guide: 0.56216 - 0.55539 = 0.00677 inches

The spring ID should enlarge by up to 0.006066 inches, so for the Delrin guide there will be at most 0.012836 inches of clearance and for the steel guide there will be 0.013966 inches. BUT keep in mind that in my setup you can easily remove the spring guides. I've not been able to do the same with commercial kits, which implies they are not leaving much room for thermal expansion.

Please note that this is an extreme example and there will always be deviations in theoretical calculation, but its certainly something to keep in mind when tuning for hot weather.

PS. Mistakes are my own - its worth double checking the work when doing your own tune.

-Marty

Nice bit of technical experimenting.....Do not forget the considerable rise in temp within a cylinder over and above that of ambient temp...
It's interesting that the front runner for piston rings (Tony Leach ...designer of the sleeveless piston) has started offering Phosphor Bronze piston rings, but originally went with PB in his original set up...getting it right first time with his new formula article in Airgun World..
He must have encountered the same issues I had with plastics..
A few others starting to switch back to metals..

On paper the Acetal/Delrin/POM C etc offer a raft of advantages, but for all their low coefficient of friction, self lube and wear resistance, the thermal expansion and contraction maybe the most important element...
It's also why (in the UK at least) a gun can be giving remarkable accuracy one day, only to drop zero point on a hot day with no apparent reason....it's plastics...
Bit of a nuisance really...

 

[scotton]

Steveoo, you are probably right regarding the Delrin thermal expansion in cases where there is no clearance. Out of curiosity, I ran some theoretical numbers on my own setup (hopefully I didn't make any errors). This is for a TX200 comparing a steel to Delrin inner spring guide:

Initial Conditions at 70 degrees:
Stainless Steel Guide OD: 0.5325 inches
Delrin Guide OD: 0.5325 inches
Spring ID: 0.5625 inches

Material Coefficient of Thermal Expansion used:
Stainless Steel Guide 9.4 x 10^-6 in/in F
Delrin Guide 50 x 10^-6 in/in F
Spring 12 x 10^-6 in/in F (I assumed the spring is of cheaper steel than the guide, thus higher CTE).

Final Conditions at 120 degrees (+50 degree swing):
Stainless Steel Guide OD: 0.55426 inches (0.00026 increase)
Delrin Guide OD: 0.55539 inches (0.00138 increase, 5.3x more than steel)
Spring ID: 0.56216 inches (0.00034 decrease)

Clearance at 120 degrees (not accounting for ID expansion due to loaded spring):
Stainless Steel Guide: 0.56216 - 0.55426 = 0.0079 inches
Delrin Guide: 0.56216 - 0.55539 = 0.00677 inches

The spring ID should enlarge by up to 0.006066 inches, so for the Delrin guide there will be at most 0.012836 inches of clearance and for the steel guide there will be 0.013966 inches. BUT keep in mind that in my setup you can easily remove the spring guides. I've not been able to do the same with commercial kits, which implies they are not leaving much room for thermal expansion.

Please note that this is an extreme example and there will always be deviations in theoretical calculation, but its certainly something to keep in mind when tuning for hot weather.

PS. Mistakes are my own - its worth double checking the work when doing your own tune.

-Marty

I did a real world test recently while trying to minimize velocity drop at high temperatures in an HW97. As part of the process, I experimented with removing the delrin piston bearings and it made no difference to velocity loss. The only thing that made any difference for narrowing the velocity drop was sizing the piston seal.

I realize you are talking about spring guides, not piston bearings. The reason I bring this up about the bearings is because thermal expansion in the bearings should have more impact than thermal expansion in the guide or top hat.

So knowing what I know about piston bearings, and reading what you wrote about spring guides, I'm more convinced than ever that the main culprit for thermal velocity drop is the piston seal (and possibly piston lube).

While shooting today in 95 degree heat, I starting getting some serious POI shift in my LGV, so I'll be trying to get that gun sorted out later today. First thing will be sizing the piston seal.

 

[jkingrph]

I don't worry about the heat messing with my springers, I worry about it messing with me. 1pm and already 101, forcast to hit 105 with heat index of 110+. I get out in that and all I do is sweat, runs into my eyes and I have problems sighting. I got out and went for my walk this morning still 80 at 6am.

 

[Jim-in-UK]

While shooting today in 95 degree heat, I starting getting some serious POI shift in my LGV, so I'll be trying to get that gun sorted out later today. First thing will be sizing the piston seal.

I tested a range of seals by measuring them at ambient temperature, putting them in a sealed bag and leaving that in the freezer for a while, then re-measuring them. The LGV/LGU seals had the second greatest thermal contraction.

Rather than sizing the seal, I would order a factory HW30 seal, which is the 25mm seal used on the early HW77, which performed best in my test, and is a straight replacement for the Walther seals.

 

[MartyMcFly]

@scotton - I think the that the old school European engineers that came up with the compound formulations for many piston seals used today never thought that anyone would be shooting in 100 degree weather. That said, I’m confident that there are more appropriate compounds from which seals can be made without the need to redesign the shape or adding excessive cost.

Does anyone know what are standard piston seals made off? I have a hunch that it’s soft Polyurethane with possible additives like Moly Disulfide. If it’s Polyurethane the CTE is about 10x of steel, but there are alternatives and fillers that can bring it down.

-Marty

 

[Steveoo]

Very good point reg the European Engineers ...

There is no doubt seals play a major part ...even major havoc sometimes with Temp variation ...
Not so sure on the piston rings quite so much as the guides ....Do not forget the springy "give" of piston rings provided by the cut slot and the pretty fast wearing in of buttons to any high spots due to their tiny surface contact..
Buttons often wearing in so fast it made me wonder if they were worth bothering with....

I'm a great advocate of steel components wherever possible...some guns OEM have proven difficult to improve on in consistency/ temp variation terms ...even though those steel components not the best of fits...and often less than super smooth...
It begs the question...

 

[MartyMcFly]

I think I’ve found a good candidate for improving on Polyurethane piston seals (assuming that’s what’s used today). AEM (Ethylene Acrylic Elastomers) is a type of synthetic rubber, also goes under the name Vamac. It has a working temperature range of -40 to 175. Most importantly it has a thermal expansion coefficient of 95 x 10^-6, which is 1.5x lower than Polyurethane’s. This stuff is often used in car applications. I wonder what it would cost to get a prototype mould made to try it out…

-Marty

 

[cjtamu]

They are all basically the same. This is the important thing to know about IR thermometer guns: "With its distance-to-spot ratio of 12:1...". The gun is measuring a cone. For this particular gun, a foot away from the target you are measuring the average temperature of an inch. All this means is that the closer you are to the target, the more accurate the temperature reading will be. And don't fall in love with the laser pointer on the gun, it can be off by a few inches. Just get as close as you can and move the IR gun around a little to get the highest temperature.

Negative. Some are made for close range readings, like this one. Adjustable emissivity is a must if you want to be really accurate. I’ve used this one for 4-5 years on RC car engines since Kim accidentally washed my old one LOL. Have compared against a contact probe, very favorable results.

Shop - Products - Infrareds - Page 1 - ThermoWorks

www.thermoworks.com