Tuning The Heat's messing with my springers.

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Mycapt65

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Apr 24, 2019
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NY, United States
I recently moved to AR and we're in the middle of a heat wave. High ninetys to a hundred with fairly high humidity. Taking the guns out of the air-conditioned house they sweat for fifteen minutes.

They shoot as expected initially and then after maybe a couple hundred shots the POI slowly shifts and the groups begin to open up. The chronograph shows the velocities drop around twenty feet per second and the extreme spread doubles from single digit to double digit. So it's measurable and not just me being fatigued. Plus if I grab another gun it shoots fine for a while as well.

I read the thread about temperature sensitive scopes. I'm sure this heat and blinding direct sunlight is messing with my scopes but the chronograph showing changes in the gun itself. You can actually feel a difference in temperature between the business end of the compression tube and the barrel. It seems the compression tube can't dissipate the compression heat completely in high ambient temps.

If I put the gun in the shade for a half hour the zero changes and the velocities and extreme spread return to normal.

Anyone else notice their guns performance dropping during extended use in hot weather?
 
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Step 1: Cheat and shoot in the shade.

20230729_150232.jpg
 
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Read about density altitude. Even at low elevation, the air density reduces markedly with heat and springers suffers from lower power due to the fact that you’re compressing air that is thinner. I shoot at 5500ft but now it’s 100F and that means my density altitude is 9000ft - about 35% less power than at sea level with a springer. PCPs are unaffected because the psi in the tank/plenum is whatever you inflate it too. In fact, they shoot better the higher the DA because there is less air to slow the projectile.
 
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I take my rifles onto a deck in rifle cases and set them sit in the shade. I shoot pistols for an hour and let the rifles sit. Less wind in the early AM. I have not noticed any issues other than the shooter when I switch to rifles, always consistent. I also shoot in the shade with a big fan to move air around.
 
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weevil said:
Read about density altitude. Even at low elevation, the air density reduces markedly with heat and springers suffers from lower power due to the fact that you’re compressing air that is thinner. I shoot at 5500ft but now it’s 100F and that means my density altitude is 9000ft - about 35% less power than at sea level with a springer. PCPs are unaffected because the psi in the tank/plenum is whatever you inflate it too. In fact, they shoot better the higher the DA because there is less air to slow the projectile.
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That's what a lot of people don't understand about springers. 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 call adiabatic heating which increases the pressure when firing that helps give a springer power.

Adiabatic Heating | Encyclopedia.com

Adiabatic heating Adiabatic processes are those in which there is no net heat transfer between a system and its surrounding environment (e.g., the product of pressure and volume remains constant). Because it is a gas, air undergoes adiabatic heating and cooling as it experiences atmospheric...
www.encyclopedia.com www.encyclopedia.com
 
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The temperature of air is a measure of the kinetic energy of those molecules that have 'translational' movement, meaning they travel in a straight line (rather than spinning or vibrating) until they collide with other air molecules, the cylinder wall (creating pressure) of the base of the pellet, which they bounce off with lower velocity, so imparting a little of their momentum to the pellet. That's what drives the pellet.

The hotter the air, the higher its internal energy. However, the higher the temperature, the more the piston seal expands, the higher the seal to cylinder wall friction, and this is more than enough to compensate for the higher air internal energy, especially if the rifle is shot fairly rapidly, as the seal gains extra heat from friction and elevated air temperatures, which cannot dissipate to the cylinder end cylinder end wall fast enough because they're hot, too.

The increased piston seal friction takes more energy from the mainspring, reducing muzzle energy.
 
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Mycapt65 said:
I recently moved to AR and we're in the middle of a heat wave. High ninetys to a hundred with fairly high humidity. Taking the guns out of the air-conditioned house they sweat for fifteen minutes.

They shoot as expected initially and then after maybe a couple hundred shots the POI slowly shifts and the groups begin to open up. The chronograph shows the velocities drop around twenty feet per second and the extreme spread doubles from single digit to double digit. So it's measurable and not just me being fatigued. Plus if I grab another gun it shoots fine for a while as well.

I read the thread about temperature sensitive scopes. I'm sure this heat and blinding direct sunlight is messing with my scopes but the chronograph showing changes in the gun itself. You can actually feel a difference in temperature between the business end of the compression tube and the barrel. It seems the compression tube can't dissipate the compression heat completely in high ambient temps.

If I put the gun in the shade for a half hour the zero changes and the velocities and extreme spread return to normal.

Anyone else notice their guns performance dropping during extended use in hot weather?
Click to expand...
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
 
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beerthief said:
"The increased piston seal friction takes more energy from the mainspring, reducing muzzle energy."
finally a simple straight foward answer to the OP question , but i really appreciate the science of the other answers also.
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I'd think it would be the opposite. The tube is going to expand a hair before the piston seal does being as the steel is in direct sunlight. That would lossen the grip on the seal a hair. I would think it mostly comes down to the air being a bit less dense in the heat. That's just an off the wall guess though.
 
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Sqwirlfugger57 said:
I'd think it would be the opposite. The tube is going to expand a hair before the piston seal does being as the steel is in direct sunlight. That would lossen the grip on the seal a hair. I would think it mostly comes down to the air being a bit less dense in the heat. That's just an off the wall guess though.
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Good observation. However, the polyurethane commonly used for piston seals expands and contracts far more with temperature changes than the steel of the cylinder. It is far from unknown for a seal sized to be a perfect fit in summer temperatures to contract so much that it loses contact with the cylinder wall on a frosty winter morning, and for a 'winter' seal to expand so much in summer that muzzle energy plummets.
 
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Sqwirlfugger57 said:
I'd think it would be the opposite. The tube is going to expand a hair before the piston seal does being as the steel is in direct sunlight. That would lossen the grip on the seal a hair. I would think it mostly comes down to the air being a bit less dense in the heat. That's just an off the wall guess though.
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Rubber actually expands more than steel or aluminum. The less dense the air is the less the piston has to compress so the less power the springer developes.
 
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DesertSilver said:
Rubber actually expands more than steel or aluminum. The less dense the air is the less the piston has to compress so the less power the springer developes.
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So as usual with a springer, anything that can go wrong will go wrong 😆

There are just so many factors playing a part in springers performance that telling which one is actually the one causing you issues is hard to pinpoint at times.
 
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Sqwirlfugger57 said:
So as usual with a springer, anything that can go wrong will go wrong 😆

There are just so many factors playing a part in springers performance that telling which one is actually the one causing you issues is hard to pinpoint at times.
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A much missed friend who passed away in 2015, who was Emeritus Professor of engineering and a self-confessed airgun nut wrote...

"The spring piston airgun is the most fiendishly complicated machine ever devised by man" ...and...

"In a springer, everything depends on everything else".
 
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Jim-in-UK said:
A much missed friend who passed away in 2015, who was Emeritus Professor of engineering and a self-confessed airgun nut wrote...

"The spring piston airgun is the most fiendishly complicated machine ever devised by man" ...and...

"In a springer, everything depends on everything else".
Click to expand...
Your friend put that very well. We're basically in an abuse relationship. If we were smart we'd walk away but something keeps drawing us back. It's like golf. Play 17 bad holes but have one amazing shot on the 18th and you suddenly have hope again and are back at it next weekend.
 
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JP806TX said:
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
Click to expand...
Their all Weihrauch springers. Most have Vortek kits the rest have Maccari kits. All were lightly lubed. Some with Krytox. Some with Almagard and some with the tan stuff that comes with the Vortek kits. My Hw50 was lubed with Krytox and found the Krytox turned sticky. I believe it was absorbed moisture from the gun's interior sweating. That guns overall performance improved when I switched it to the tan Vortek grease. All the guns run Vortek piston seals. I did try a traditional JM parachute seal in my HW30 and it made less power and had the same gradual power loss during extended use.

I think Jim hit the nail on the head, that heat and extended use is causing greater than normal piston seal expansion. The extra drag from that is probably what created my power loss, widened ES and POI issues.

I'll just have to acclimate the guns better and switch them out sooner.

Thanks all for the replies.
 
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Because they occupy the full width of the cylinder, HW seals have more material to expand and contract than seals that surround the central front face of the piston. In the UK climate, which has less extremes of hot and cold than many countries, seal expansion/contraction tends to manifest itself in POI shift (because it changes the point in the recoil cycle that the pellet exits the muzzle) rather than dramatic muzzle energy shift, and it is the reason why the HW97, which used to dominate the UK recoil class HFT circuit, has been largely usurped by the TX200.

If you want to know which seals will be less affected by temperature, measure their diameters, pop them in a plastic bag and leave them in a freezer for a while, then measure them again. The one that has contracted the least will be more resistant to temperature fluctuations.
 
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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...
 
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