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Finally, Springer altitude testing completed with pics and decent data volume

October 27 2009 at 11:12 PM
  (Login Dmitry_Smushkov)


Thank you

First, I'd just like to thank my handful of awesome customers; especially the guys who helped make this project possible. Too many times, we hear about deadbeat customers and deadbeat tuners, without stopping to acknowledge the many business relationships that enrich our sport.

My story

Years ago, before I could afford a PCP, and before there was an affordable PCP, I started working on springers with some success. Unfortunately, they were somewhat limited for me by their sensitivity to altitude and general finickiness and hold sensitivity. Eventually, I could just afford a good PCP and it was pretty well game over for the fussy springer.... Well, not exactly. Shooting a PCP gave me an epiphany. Why should I have to work so hard to enjoy a springer? Shouldn't the springer work for me and not the other way around? With that enlightened attitude, I developed a whole new approach to soft tuning springers to make them worth owning even after investing in PCP's. The side benefit was that some were also less sensitive to altitude changes.

This project

This project started out of curiosity. I live in Colorado and hunt, most recently, from 4,700 ft to 10,000 ft +, but then became even more important. You see, by posting about my specialization in 12 ft-lb range tuning, I started attracting FT guys. Problem: that meant that I had to tune to spec at sea level, not just somewhere around 12 ft lbs! Well, how would I ensure that my 12 ft lbs at 5,000 ft = 12 ft lbs at Sea Level? As with all of my projects, it took me a few years to gather the necessary equipment and to set aside the time to complete all these tests. I had previously performed random tests, but until I bought a GPS, I did not have a reasonably accurate estimate of the elevations for the velocity tests. So, finally, everything came together this year. This research has made me a better tuner and I hope it will give you guys some guidance in your decision-making.

In case you don't feel like reading the whole thing, below is a list of general conclusions. Here's the gist:

1) There is no single rule of thumb to estimate fps velocity drop for all springers, but there are some % drop ranges you may find useful.
2) It is important to reduce velocity drop when tuning a springer for altitude, because change in velocity will affect your POI. Unfortunately, I did not test any single gun model in multiple calibers. Another approach is to look at the drop in power, and then calculate the drop in velocity. You can examine the data below and decide which trend would be best-fit estimate for your gun/caliber.
3) Tuning for power and tuning for altitude sensitivity are opposing goals, but a soft tuned springer will not necessarily be less sensitive to altitude change. The analogy (conceptually not technically) that could be made is it's like the difference between tuning an unregged PCP for max power output or max shot-to-shot consistency. You are either trying to get the most power from the highest available volume and pressure (sea level), or minimize velocity drop as the pressure drops (climb in altitude).


[linked image]

Using a Garmin Rhino GPS with downloaded Topo map, and an F1 Chrony, I drove up into the mountains and tried to find at least 3 safe and level test locations. There were many variables, which I could not control, but I hoped that consistent procedures would result in reasonably valid results. I sample weighed the pellets to confirm factory specs. Each gun was tested at all altitudes on the same day. 5 warm-up shots were fired before shooting 10 shots over the chrony. Velocity was then averaged and rounded to the nearest 5 fps. Pellet selection was based on inventory at hand, while omission was based on poor accuracy performance (ex: CPs were not altitude tested in HW50S). Once I entered my data into Excel, I generated trend lines to give me some approximation of what the power and velocity should be at untested elevations.

Testing and results

The 2-scale graphs do not have corresponding scales (ex: 770 fps is not 9.5 ft lbs). They are just superimposed to show more data on one chart.

CZ 634 .177
This gun was tuned to factory spring power output, but using a much softer R7 spring. You can search the forum for one of my posts on tuning this gun.

[linked image]

Beeman R7 (HW30S) .177
This was a customer gun. It came to me with a stiff .120" wire and 0.520" coil ID spring installed. I tuned it with JM's Universal Mini Spring with 0.105" wire and 0.560" coil ID, which is even softer than a regular R7 spring. (The smaller the wire and the larger the coil ID the softer the spring.). I wanted to increase the power and reduce the cocking effort of this gun for my customer, which is what you see in the graph. Something else you see is that in received condition it was less altitude sensitive than post-tune. I wanted to show this as an example of a tune not designed for altitude, but for better performance closer to sea level.

[linked image]

Beeman R9 (HW95) .20
The tested gun was soft tuned to 12+ ft-lbs using JM's R6 spring. This gun has lately been one of my primary hunters. Its altitude sensitivity is low, and I thought about improving it further. In the end, I left the gun alone, as I am very happy it.

[linked image]

HW97K .177
This was another customer gun. This gun was factory condition. Unfortunately, in received condition the gun dieseled way too heavily to get good data. Customer tune spec. was 11-12 ft. lbs., so I re-tested after the tune. As it turned out, I overshot 12 ft-lbs just a hair. We got the rifle shooting to spec, but I did not have a chance to re-test it.

[linked image]

Beeman R1 (HW80K) Carbine .177
This gun was tested in factory condition. So, here you go. If you want a factory gun not sensitive to altitude, this is what it takes. Clearly, in factory condition, this gun does not even come close to the potential of its potent powerplant, but it also means that there is no practical altitude sensitivity. I had to run this test twice just to be sure, and replicated the results. The large compression volume of this rifle alone does not explain the results. Since this is the only rifle I tested with a 30mm compression tube ID, the rest being 25mm and 26mm, I wonder if that is the major contributor. OH NO!!! Now I MUST buy another gun in the name of science!!!! To verify the chamber diameter contribution Ill need to get an HW35, which has same chamber diameter but shorter stroke, and, therefore, lower compression volume. Ill keep you guys up to date.

[linked image]

Air Arms TX200/ProSport .22
I wanted to conduct this test with the ProSport alone, but it was in pieces for refinishing for a long time. Since the ProSport and the TX200 have identical powerplants, I substituted TX200 for initial tests. I first tested a factory condition TX200. I then tuned it close to factory power, but with a much softer JM R6 spring. Based on this test and my R9 test I knew I needed a softer spring for my ProSport altitude tune. I used one of three JM R8 springs I had. Unfortunately, I found out that JM has discontinued these springs.

[linked image]

HW50S .22
I first wanted to use an R8 spring, but found it has been discontinued while working with the ProSport. I tuned it with the Universal Mini Spring, using what I had learned from all other tests, and it worked out far better than my expectations. The spring I used is just about maxed out here, and JM just does not have the demand to make a large variety of soft springs. It is now my primary cross-altitude springer.

[linked image]


Here are some graphs of overall % drop per 1,000 ft of elevation gain. I hope these numbers will help you guys draw some general conclusions.

[linked image]

[linked image]

Looking forward

Clearly, many more tests that could be performed, but time, weather, and finances all conspired against me. I now have some ideas, and will continue to keep y'all up to date. I'll be taking on more customers starting January 1, so let me know if you are interested in my work etc. I do have 2 discontinued R8 springs left for those interested in a TX200, ProSport, R9, HW77, HW97 altitude tune.

Thanks y'all,

Dair Designs

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(Login Dmitry_Smushkov)

May also be useful knowledge for FT guys and flatlanders nt

October 27 2009, 11:14 PM 


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Jeff P
(Login pad617)

Naaahhh, I do see why FT'ers need this info...

October 28 2009, 11:59 AM 


Keep it up Dmitry, great work.

Jeff P

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(Login yuganz13)

Very nice one of the best reads ever

October 27 2009, 11:18 PM 

Lots of helpful info. I am myself putting together a HW80 sporting a R11 barrel and with a 13 ft/lb kit for high altitude use.
Many thanks for sharing your tests.

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(Login RBest)

Some good info there Dmitry

October 27 2009, 11:29 PM 

While I've never been able to actually tune a gun at (say) 6000 feet, I became aware that a softer spring could yield fine results. At altitude some guns are just simply oversprung and the idea that an even stronger spring is needed to compensate for lost air density, will turn the gun into a jackhammer. One thing I'd love to test out in this regard is (for example) leaving a factory spring in the gun BUT reducing the transfer port size to see if a proper cushion of air could be generated to soften the shot cycle. Great work! Regards, Russ

"The Universe is comprised mainly of two things.. hydrogen and ignorance."
John Dobson
Inventor, astronomer and metaphysical thinker.

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(Login Trojan1994)

Great Post Dmitry!

October 27 2009, 11:31 PM 

Thanks for the efforts to collect the data and present it in such fine fashion!!!! happy.gif Your R7 tune sounds very interesting!!!



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(Login pneuguy)

Spectacular! Thanks for posting this, Dmitry. Prior to this...

October 27 2009, 11:40 PM 

...about all we had was the rough guess that springer power was roughly proportional to air density - which predicted that, since air density declines by roughly 3% per 1000', muzzle energy will as well.

Interestingly, I just ran a rough average over all the examples in your last plot.

Although of course the case-by-case variability is huge, I get: 2.5% / 1000'


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(Login rickpetersonms)

Could the less than expected power loss be because there was still (nearly) enough air

October 28 2009, 3:04 AM 

trapped between the piston and the pellet to transfer enough force to get the job done? Would the 2-1/2% (per 1,000 feet altitude)
loss in power be accompanied by a larger than 2-1/2% per 1,000 reduction in noise due to less air following the pellet out of the barrel?

Another thought ....Does the lower density increase the "lock-time" (apologies to Steve and Larry) because the piston has to travel farther to build enough pressure to budge the pellet?

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(Login Dmitry_Smushkov)

I can't say I noticed these effects, but theoretically....

October 28 2009, 4:17 AM 

As far as noise, most springer noise is mechanical not compression - in my experience. This may be different for the super-duper magnum springers. I can't say I noticed any increase in noise level. Lock time may be a give and take. Yes, the piston has to travel slighlty farther, but it also sees less resistance, so it may be traveling faster.

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(Login HW3)

I had always wondered about this...

October 28 2009, 6:49 AM 

It almost always comes out lower than 3* and some guns definitely fair better than others. I was always trying to identify the variable, and while I tend to believe it's mechanical in nature, I could just never put my finger on it (difference in stroke perhaps). What I did find on Super Magnums in thin atmosphere was that the piston seals can really fry in the worst imaginable way. Pronounced...Almost inexplicable damage like you just wouldn't believe, and any seal issue would initiate a degenerative chain reaction. Naturally light pellets are just begging for trouble. Noise tends to be higher due to detonation, but again that's with Super Magnums. My overwhelming generalization was the lower the stock velocity the better, but that's far from the actual truth. What about using higher heat resistant seals or lubes if there is such a thing ? I'd have thought the manufactures would have already gone to that extreme just for reliability purposes.

This is quite possibly the single best (Most thorough experimentation) post I've seen on the subject ! You'd think that since it affects all the local shooters here they could actually get organized and delve into it further ? Alot of guys just switch to PCP's and enjoy the benefits (Lower air density definitely benefits Precharged Pneumatics), but it's unrealistic just to eliminate springers altogether...Hell I'd move if that were the case !!!

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(Login rickpetersonms)

I've never had a springer apart, but could the piston seal be banging into the end of the

October 28 2009, 10:18 AM 

tube with the thin air? Almost like a dry-fire.

In roundish terms, let's say there is 2-1/2% per 1000 feet ASL less resistance.

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(Login gubb33ps)

Great post.

October 28 2009, 7:04 AM 

Really the best report on altitude/vel. loss I've read.

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(Login DavidEnoch)

This has been a great month of good post.

October 28 2009, 8:25 AM 

I have suggested to Steve that he archive this post along with a couple others this month.
I have to applaud your hard work to do both the research and to present it to us in such a format. I am very impressed at the performance you are getting with softer than factory springs. Good luck with the tuning business.

David Enoch

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(Login rcannon409)

THANK YOU!!!!!!!!!!

October 28 2009, 8:48 AM 

I appreciate your taking the time to compile this info. I own a couple of the guns on your test list and the figures you show at 4000-6000 feet match what I'm getting exactly.

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Paul in Tucson
(Login PelletPaul)

Thanks for the hard work Dmitry

October 28 2009, 8:48 AM 

Over the years I have asked this question many times with only guesses. This test took a long time and we appreciate the hard work and time you took to complete this project. Thanks again. Paul in Tucson

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(Login TKO22)

From some work with the GE CF-6-6 jet engine...

October 28 2009, 9:29 AM 

we did for the NTSB (CF engine used in the tail of the DC-10 and the F-16), we found that the air temperature differential at altitude would slightly cancel the air density differential of an air compressor.

Assuming that the airgun tests were conducted "vertically" (that is the tests were conducted directly above the other,) we will see an air temperature change. The sudden compression of the air during the shot generates heat, and the differential between the temp. of the air in the res compared to the temp. of the same air under compression will generate "more pressure".

Offseting the heat differential pressure increase would be the decrease of the density of the beginning air charge.

There is a point where the temperature of the air ceases to decrease (around FL 360) while air density will continue to decrease, and that's where we would expect to see a linear slope plot of pressure decrease within the pump.

Temperature measurements at each altitude would also aid in further discussion of the results.

Very good tests!

Mike T.


Added: Our work with the GE engine was the result of Flight 232s rear engine coming apart at cruising altitude over an Iowa corn field and our computer modeling of the fan disk event.

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(Login dj6mm)

This helps explain something

October 28 2009, 10:01 AM 

When I was a junior shooter I had the opportunity to go to the U.S. Olympic Training Center in Colorado Springs and train for 10m air pistol. The first year I went back I was shooting a Beeman M10, a recoiless break barrel pistol. I lived in Yorba Linda, CA, not too much above sea level, and when I went back to the Training Center at 7000 feet, or something like that, my first shots to sight my gun in barely hit the bottom of the target. I had to crank my sights way up to get in to the ten ring.

A year later I was invited to go back again, but this time I was shooting a FWB 65. I was expecting the same kind of altitude change, but with the FWB my first shots were just low in the 9 ring, hardly any change at all.

For years I wondered why the big difference between the two guns, now I at least have some explanation of what may have been happening.

Interesting stuff.

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James Mills
(Login jamesmills)

Thanks for empirical testing

October 28 2009, 10:15 AM 


Thank you for this posting and the effort you put into this analysis. Being a Denver resident, and a spring gunner, I greatly appreciate this work. We need to get the Denver area airgunners together again for a shoot - not today, of course... It should be a big dig out come Friday morning after all this snow.

Best regards,

Jamey Mills

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(Login CrimsonSky)

Great Info, Thanks!

October 28 2009, 12:33 PM 

I'm about 2k feet up in the mountains, doesnt have a great impact on springers, but it was nice to read some serious altitude info.



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