Indoor Shooting Observations and a New Milestone for Me

michaelthomas

michaelthomas

www.thomasrifles.com
When I built the last couple of rifles for Paul and Mark, I brought a third one up alongside them for my personal use. I finally got everything buttoned up and began testing it last weekend.

I shot Paul's rifle at our last match before shipping it out to him, and was able to shoot a 750 57x at LV power. I had honestly commented to my friend Joe that I wasn't sure Pauls rifle was capable of shooting a 9....because I had never shot one in all of it's testing....lol. All of the testing and shooting was done with JSB 8.44's right out of the tin. I attributed this performance initially to only one specific difference in his gun and my former guns.....which was the slow twist LW that he got from Dan.

It wasn't the only difference, though. I built the valves for all three of these rifles differently than all of my previous. They took on average 10-12 volts (which is a lot) less to produce the same power level. I wasn't sure of the individual significance of this at first.....but now, as I look back over the individual performances of these three guns with 3 different barrels I am seeing something different.

Marks' barrel was a standard twist poly LW that was not noted for it's stellar performance....especially at LV power. It was also a few inches shorter than full length. Mark had mentioned that it wasn't anything to shout about, and was maybe a 245 shooter. I was able to shoot a 750 39x or so with it using the unsorted JSB 8.44's, too. The barrel did not like being clean, and produced the best score of 250 18x after 2 cards and sighters were through it. I don't remember exactly what the first 2 cards were.....250 10 and 11x or so.

So far I have been able to shoot 8 cards with my new gun. It is a Plain Jane standard rifling LW barrel that is one of the original 5 I ordered nearly a year ago. So far every one of those 5 were capable of 250 15x in my old platform. This is the first test of any of those 5 in the new valve format gun.

I shot 2 cards last weekend with it, and they were 250 20x ,and 250 19x.

Yesterday I got the time to shoot 6 more. I shot 250 17x, 250 21x, 250 19x, 250 21x, 250 19x, and 250 20x.....in that order. So a 750 57x, and a 750 60x. These were also with JSB 8.44's from the tin.

This barrel seems to like being freshly cleaned.....the first 250 17 x was shot without cleaning, and approximately 75-100 chrony pellets and many sighters through it. The remainder of the cards were shot with the barrel cleaned prior to each card.

I have also been experimenting quite a bit with the level of tune. When I say tune, I mean the balance of power and solenoid strike. My former tune guide was to turn up the voltage until the gun would shoot no faster.....record the speed, then reduce strike until the velocity was somewhere between 30 and 40 fps less than the max. This had produced the best scores for me, despite it going against the prevailing logic that says that the tighter the spreads the better a gun should perform. If I turn up my current gun to near max power for a given reg pressure, I can obtain SD's of 0 and ES's of 1-2 FPS on my Comp Electronics chrony. It rounds to whole numbers, so in actuality 0 only means something less than .5. At 30-40 FPS below the max.....I see SD's of 1-2 and ES's of around 7.

I placed an indicator on the top of the barrel to measure muzzle rise at the different settings. At the 30-40 FPS below max tune....I see a movement of roughly .0002". This is with the gun resting on an aluminum block in the front and the rear just resting on the countertop. Near the max power setting (where the tightest velocity spreads occur) I saw over 5 times that amount. Shooting with no pellet in the chamber, at the 30-40 setting produced a movement of over .006" It happened so fast that I had to get a slo mo video app for my phone to actually be able to define the movement.

This past testing session was done somewhere in the middle.....with ES's of around 3-4. It seems as if it has not tipped the scale over the optimum accuracy vs tightest spread at this setting. This tune is about 20 FPS below maximum velocity for given reg pressure.

I gather from this that the smallest amount of muzzle flip could potentially equate to the smallest vertical deviations, but since this occurs where the velocity spreads are the highest (amongst the two extremes) ....there is somewhat of a tradeoff. Moving my tune to obtain the tightest spreads results in more vertical barrel movement, and potentially greater vertical stringing due to that in itself.

My original logic was to set the gun for the tightest spreads, then use a stripper to get rid of the excess air from that tune. I was never successful in reaching the consistent 19-21x's with any iteration of stripper and the "louder" tune......and so far I have not been able to isolate the actual stripper effects from the weight tuning effects of the stripper. I feel like the greater muzzle flip is a result of harmonics started long before the pellet leaves the barrel.....so it cannot be attenuated by something after it leaves.

So at the moment, I'm trying to find the breakover line where they (muzzle flip and ES) both balance themselves out for the greatest overall good.

Unfortunately......simply turning the voltage up and down alone results in velocity differences, so the experiments are kind of a pain for me because they involve very slight regulator adjustments in conjunction with voltage to keep the average velocities the exact same so the tests are as valid as can be.

Overall, I feel that my initial goal to absolutely minimize what happens before the pellet begins any movement in the barrel is a sound premise and has shown good results in every one of my guns and every barrel that has been tried in each.

I do intend to try my other plain LW barrels in this platform as well. Since I have an established baseline with them already, I should easily be able to see any improvements that may be directly attributed to the new valve platform.

Every time I feel like there is a obvious logical connection between an particular action and a following result.....I end up finding other not so obvious connections that could possibly weigh in more heavily than originally expected.....lol.

Mike
 
Mike,

Thanks for sharing your results. It certainly shows how much we really don't know about air rifles and/or how different they are from their rimfire cousins.

A 750-60X is the ceiling many have been trying to reach during the indoor season. Congratulations.
 
Mike,

Great post! I found it both fascinating and thought provoking. Considering I don't even own an air rifle and I'm more than a little unfamiliar with exactly what you're doing, I think I got the gist of it.

I wish I lived just a little closer to you because I'd love to observe your testing at your place or in my tunnel. On second thought maybe that's not a good idea....I'd probably end up selling one of my rimfires to fund an air rifle purchase. LOL

Landy
 
Thank you Michael for share your findings with us. Your detailed explanations, along with your results, only will make us want one of your guns all the more. Add to that the fact they are now starting to find their way into the field and will begin proving themselves shoulder to shoulder against the more "traditional" guns we are all so use to will give us an even better window into what they are truly capable of. I know I for one am excited about the possibility of being able to "test" one, or even two, of your creations while at the N.E Regionals coming up the end of June.

Keep up the good work, and never stop thinking outside of "the box".

Dave Shattuck
 
Thanks guys.....I really don't know what I know, I'm just trying to wade through this as logically as I can. :D

At 25 yards, I calculate pellet displacement to be somewhere around 38.5 times what is happening at the exit of the barrel. This is based on a .010" movement, and may not be linear....but it's good enough for the sake of comparison at this small amount.

So if my barrel is nodding .0002" at the tip.....that translates to a potential of .008" at the worst case exit scenario. Unfortunately.....at this setting of tune, I see ES's of 7.....maybe even 8 sometimes. That potentially translates to about .038" of vertical displacement for velocity difference alone.

So setting the tune where I can hold 1-2 FPS makes the barrel jump 5-6 times as much....or maybe .040- .048" at the target, but the velocity differences only account for .010".

Looking at that information, it would seem that taking the gamble on the "louder" and closer spread tune and hoping that the pellet doesn't always exit at the extremes of barrel nod would be better odds. It's never better that way in my testing, though. It is always at least 3-4 x counts lower at the minimum.

My only explanation of this is that velocity is not velocity. Early on.....before I had regulators in my guns.....I noticed the bell curve of velocity vs pressure that was produced. Everybody knows about that. But I clearly saw that the pellet reacted differently when it was on the near side of the bell compared to the far side.....even though they may have produced the same velocity.

This plateau of near constant velocity may last for 2-3 hundred psi or more in an unregulated gun. When I am able to get my rifle to hold 1-2 FPS spreads, it's because I'm taking advantage of that natural self regulating property by setting my strike to work in that range. The reg could potentially vary a significant amount and still produce a similar velocity. Because the plenum volume is limited after the regulator.....the stable window or plateau won't ever be as large as it was unregulated......but it still exists on a smaller scale.

It may be that the greater spreads are caused by the fact that the air has done most of it's pushing while the pellet is still in the barrel and since the pellet is on coast while still engaged.....frictional differences after the pellet stops accelerating could account for the velocity change.

When the rifle is on the louder setting.....the pellet probably maintains an acceleration it's entire time in the barrel (although slower).....so frictional difference is potentially minimized resulting in tighter spreads. But.....the barrel dances significantly more......and groups open up.

So is the detrimental movement caused by the extra air exiting......or the difference in the way the expansion has taken place?

I don't know.

I only know that right now my rifle produces better results at the target when the spreads are a little higher.....and when the amount of energy needed to set the valve in motion has been reduced.

Please comment. :D

Mike
 
Mike,

Now that I understand your thinking, it all does make sense to me. The problem is, how to take your findings and use them to improve the performance of a typical hammer/spring air rifle.

"when the amount of energy needed to set the valve in motion has been reduced."

This is a perfect example of our problem. The hammer springs we use are not infinitely adjustable. First, alternate springs are not always easy to find and often have widely varying power levels. Next, we put the spring in place and play with adding pre-load to increase/decrease hammer strike. Too much pre-load puts us at risk of hammer bounce, which may or may not release unnecessary air but certainly adds to any vibration signature. Too little pre-load and valve opening can be compromised depending on air pressure levels and results in pellet velocities that fall off rapidly.

"If I turn up my current gun to near max power for a given reg pressure, I can obtain SD's of 0 and ES's of 1-2 FPS on my Comp Electronics chrony. It rounds to whole numbers, so in actuality 0 only means something less than .5. At 30-40 FPS below the max.....I see SD's of 1-2 and ES's of around 7."

This is another example. On my Sumo, in Open Class, this exercise could be done but the spring would be so stiff that cocking upsets the rifle in the bags. One spring change might bring velocities down 30-40 FPS but it is hard to be sure that the original spring was getting me to that "max power" setting. We almost always use cocking force as a determining factor, when in actuality, that could be a mistake.

Obviously, some of our notions are going to need to be set aside in order for the rest of us to move forward.

.
 
michaelthomas said:
So if my barrel is nodding .0002" at the tip.....that translates to a potential of .008" at the worst case exit scenario. Unfortunately.....at this setting of tune, I see ES's of 7.....maybe even 8 sometimes. That potentially translates to about .038" of vertical displacement for velocity difference alone.

So setting the tune where I can hold 1-2 FPS makes the barrel jump 5-6 times as much....or maybe .040- .048" at the target, but the velocity differences only account for .010".
Click to expand...

Mike,

All way over my head I'll be honest, but some of your comments in the above range a bell.

A little light reading, which may or may not be of assistance: http://www.geoffrey-kolbe.com/articles/rimfire_accuracy/tuning_a_barrel.htm

Obviously undertaken with a rimfire, but some of the information may transfer to air rifle.

Further reading here: http://www.geoffrey-kolbe.com/articles/rimfire_tests.htm

Brian
 
Brian,

I have followed Dr. Kolbe's work very closely. Earlier, I thought much of what had been learned about rimfire accuracy might apply to air rifles. Today, I think there are more differences than similarities.

Bedding is viewed as a critical element of an accurate rimfire rifle. Air rifles get bolted to aluminum stocks and 2X4s, shoot great. The pressures generated by rimfire ammo is well beyond what happens, even with an Open class rifle, so the harmonics are completely different. I do think barrels make a difference, chambers are important and crowns can never be done with a brass screw.

What is great, is that we are learning and guys like Mike, Dan and Chip are leading the way. Even better, is that they are willing to share.
 
Stephen,

I have to be honest; I hold some reservations about electronically fired air rifles (sorry).

It does appear that these rifles hold some technical advantage over the more traditionally operated air rifles and the harmonics of the rifle may well be playing a major role in this. The scores being achieved, albeit presently indoor, seem to be unobtainable with anything less (although much more information is required). Whether this is a good or bad thing for the sport I’m not sure.

Both the USARB and the BIPM presently accepted these rifles. It will be interesting to see how this technology develops and if in fact it will be a considered progress or a step to far which further removes the input of the shooter from the scoring process.

Brian
 
I tink I get it, My louden poofer is going to get whipped by a mouse duster.

Seriously_ like in center fire, max charge/velocity seldom begets max accuracy.
 
Brian_K said:
Stephen,

I have to be honest; I hold some reservations about electronically fired air rifles (sorry).

It does appear that these rifles hold some technical advantage over the more traditionally operated air rifles and the harmonics of the rifle may well be playing a major role in this. The scores being achieved, albeit presently indoor, seem to be unobtainable with anything less (although much more information is required). Whether this is a good or bad thing for the sport I’m not sure.

Both the USARB and the BIPM presently accepted these rifles. It will be interesting to see how this technology develops and if in fact it will be a considered progress or a step to far which further removes the input of the shooter from the scoring process.

Brian
Click to expand...

Brian,

This is a area that I'm concerned with and IMHO is a priority for the new directors. The USARB as of present follows the current World/European rules for LV and HV, for Club, Regional and National matches. Their current rule states no electronics period.

So where does that leave a few who are currently using electronics and for some who will most likely purchase down the road. USARB does have a U.S.hybid class which allows the use of electronics but unaware that a club has posted any results in that class.

Most likely when new rules are set by the directors they will not take affect till next year, so in the meantime where does one classify a competitor under current rules, using electronics.

Regards,
Joe
 
Joe,

It is one thing to, as Brian put it, have reservations or be concerned and quite another to squash new technology. I can appreciate the need to be part of a bigger organization, the WRABF, but their shortsightedness is the result of votes from countries who fear that they will be left behind. For the USA to be shackled to the lowest common denominator should never be an acceptable position. The USA should not relinquish any advantage, real or otherwise, due to the arbitrary opinions of those who fear what they do not understand.

I predict that in 20 years, this type of design will dominate in competition and have a major role in further PCP development.

At some point the board must determine if our association with the WRABF is helping us or is a hindrance.
 
At 25 yards, I calculate pellet displacement to be somewhere around 38.5 times what is happening at the exit of the barrel. This is based on a .010" movement, and may not be linear....but it's good enough for the sake of comparison at this small amount.
So if my barrel is nodding .0002" at the tip.....that translates to a potential of .008" at the worst case exit scenario. Unfortunately.....at this setting of tune, I see ES's of 7.....maybe even 8 sometimes. That potentially translates to about .038" of vertical displacement for velocity difference alone.
So setting the tune where I can hold 1-2 FPS makes the barrel jump 5-6 times as much....or maybe .040- .048" at the target, but the velocity differences only account for .010".
Looking at that information, it would seem that taking the gamble on the "louder" and closer spread tune and hoping that the pellet doesn't always exit at the extremes of barrel nod would be better odds. It's never better that way in my testing, though. It is always at least 3-4 x counts lower at the minimum.
Mike,
I can almost guarantee pellet displacement at the target won't have a linear relationship to the measurements you make at the muzzle, but you're correct about it probably being "good enough" for comparison purposes.
One problem will be the additional data (testing) needed to overcome the noise generated by this non-linear rate of dispersion at the target so as to insure conclusions based on it are statistically valid.
The bigger problem may be that what you're measuring may be meaningless if air rifles behave similar to rimfires or centerfires, because what needs to be measured is the angle the crown is pointing and not necessarily the motion at the end of the barrel.

It may be that the greater spreads are caused by the fact that the air has done most of it's pushing while the pellet is still in the barrel and since the pellet is on coast while still engaged.....frictional differences after the pellet stops accelerating could account for the velocity change.
When the rifle is on the louder setting.....the pellet probably maintains an acceleration it's entire time in the barrel (although slower).....so frictional difference is potentially minimized resulting in tighter spreads. But.....the barrel dances significantly more......and groups open up.
Friction is a significant force from about 6" on in rimfire and friction robs the bullet of a given amount of energy per unit length traveled up the barrel. Since the energy of the bullet goes as the velocity squared, slower bullets will slow down quicker than faster bullets. That means friction or coasting is your enemy and not the friend you hypothesized, "if" we're on the same page and centering this discussion on only the velocity stats.

How much of what I've said translates to air guns? I don't have a clue and we'll just say it's food for thought.

Landy
 
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Landy,

I was with you until you said, "That means friction is your friend and not the enemy you hypothesized".

How about taking that a step or two further? Thanks.
 
sgeorge said:
Landy,

I was with you until you said, "That means friction is your friend and not the enemy you hypothesized".

How about taking that a step or two further? Thanks.
Click to expand...

Steve,

I'm either an idiot or had a senior moment....or both! LOL
Thanks for pointing out my low IQ and inability to express my thoughts concisely. LOL

Here's what I meant to say and mangled it horribly:
That means friction or coasting is your enemy and not the friend you hypothesized, "if" we're on the same page and centering this discussion on only the velocity stats.
To expand on that, it means shorter barrels or less coasting in a longer barrel will improve velocity stats but may not necessarily improve precision/accuracy.

I've also edited my post above and I hope to Hell I've got it correct this time.

Landy
 
Landy,

Of all the possible idiots, you are not one. After we talked, I thought some misplaced key strokes might be to blame. If you and Mike were in the same zip code, things would get even more interesting. Your testing methods and application of statistical analysis might actually get us some answers but, for now, simply having an improvement in results is enough. Again, when lurking and reading Mike's posts, barrel indexing is being utilized. Sometimes, that gets lost in all the excitement of off the chart X counts. A couple of pictures of your indoor testing facility might be nice about now and, no, they don't have to show everything clean and neat.
 
Steve,

I'm short on time cuz I've got a guy from Minnesota arriving tonight and we're gunna engage in a marathon testing session lasting thru the night and into tomorrow afternoon.
The pics I'm posting were already in my Photobucked account, so I just grabbed a bunch of them and there are probably way more of them than anyone wants to see.

Mike,

I feel like I might be derailing your thread by posting these pics. If you wish, I'll delete these pics and put them elsewhere with a link.

Landy

Construction:
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Indexing5.jpg


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Indexing2.jpg


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S1.jpg


Chronograph Calibration:
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Calibrated & Ready to Transport Downrange:
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Downrange:
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Wow Landy, your facility sure beats mine! I'm lucky to get 23Y when shooting diagonally across my barn. But yours? Don't we all wish we lived in Nebraska.

Very nice.

Dave Shattuck
 
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