How does rifling twist rate affect velocity and/or accuracy? Part 6

by Tom Gaylord, a.k.a. B.B. Pelletier

Part 1
Part 2
Part 3
Part 4
Part 5

This is the sixth part of a very long test in which we’re looking at the effects of the rifling twist rate on accuracy and velocity. If you have landed here and not read the first 5 parts of the report, I advise you to do so before reading today’s report because I’m not repeating a lot of what went into this test.

I’m using an AirForce Talon SS rifle in .22 caliber because it’s accurate and also because the barrels are easy to change. Dennis Quackenbush has made two barrels with twist rates of 1:12 and 1:22 for this rifle, but today I’m testing the Lothar Walther barrel that comes standard in the gun.

Today, we’re looking at the accuracy of the factory barrel that has a 1:16 twist rate. I’ll shoot 10-shot groups at 3 power levels with 2 different pellets at 10 meters and 25 yards. That means I’m shooting the rifle 120 times for today’s report. Some of you have wondered why it takes so long between reports — this is the reason.

What you’ll see in today’s report was actually shot on two different days because I cannot maintain concentration for 120 continuous shots. So, I shot the 10-meter targets on one day and the 25-yard targets on another. All shooting is off a rest, to take as much of the shooter out of the equation as possible.

Ten-meter testing

First up is the 14.3-grain Crosman Premier pellet with the rifle’s power set at zero. Ten pellets made a group measuring 0.495 inches between centers. If you’re interested in the respective velocities of each pellet at the various power settings, you can find that in Part 2.

Talon SS rifle Premiers 10 meters power zero
Ten Crosman Premiers went into 0.495 inches at 10 meters on zero power.

Next, I fired 10 15.9-grain JSB Exact pellets on the same power setting. The group measures 0.10 inches between centers. That’s for 10 shots! Don’t tell me that a Talon SS isn’t accurate!

Talon SS rifle JSB Jumbo 10 meters power zero
JSB Jumbos were much tighter at 0.10 inches. That’s 10 shots into one-tenth of an inch!

Next, the power was dialed up to setting 6, and I shot a group of Premiers. To see how the power settings are calculated, look at Part 2. Ten pellets made a group that measures 0.404 inches between centers.

Talon SS rifle Premiers 10 meters power 6
Ten Premiers went into 0.404 inches at 10 meters on power setting 6.

Then, JSBs were shot at the same power setting. This time, they landed in a group that measures 0.092 inches between centers. This is better than a lot of 10-meter rifles can do for 10 shots at the same distance. People will argue that they can do better, but it’s always a 5-shot group they show.

Talon SS rifle JSB Jumbo 10 meters power 6
Now, THAT is a group! Best one of this test and better than many 10-meter target rifles, it’s 10 shots on 0.092 inches. It looks vastly smaller than the other small group above, but this one has more paper that closed back on the group than the first one.

Finally, we come to power setting 10. Premiers grouped 10 pellets in a tight 0.247 inches. This group is very round, indicating the barrel likes this pellet at this power level.

Talon SS rifle Premiers 10 meters power 10
On power setting 10, Premiers grouped in 0.247 inches. Impressive!

JSBs at power setting 10 finished the 10-meter testing. They landed in a group measuring 0.299 inches between centers.

Talon SS rifle JSB Jumbo 10 meters power 10
On power setting 10, the JSB pellets opened back up to 0.299 inches. It’s still pretty good.

25-yard testing

Now it’s time to move back to 25 yards and test everything again. First up is the Crosman Premier at power setting zero. Ten made a 0.48-inch group.

Talon SS rifle Premiers 25 yards power zero
At zero power and 25 yards, 10 Premiers made a 0.48-inch group.

JSBs came next. On power setting zero, they made a 0.571-inch group.

Talon SS rifle JSB Jumbo 25 yards power zero
On setting zero, 10 JSB Jumbos went into 0.571 inches.

Then, the power was dialed up to 6, and Premiers were fired again. Ten went into a 0.654-inch group. That was the largest group fired with the factory barrel in today’s test. This group was also spread very horizontal.

Talon SS rifle Premiers 25 yards power 6
Premiers opened up on power setting 6 at 25 yards. This 0.654-inch group was the largest of this test.

JSBs made a 10-shot group that measured 0.569 inches between centers. This group was also horizontal in shape.

Talon SS rifle JSB Jumbo 25 yards power 6
JSB Jumbos opened up a bit on setting 5, as well. These measure 0.569 inches between centers.

Finally, the power was dialed up to 10, and 10 Premiers were fired again. This time the group shrank to 0.329 inches. I call that a significant result; because not only is this group much smaller than the group fired on power setting 6 with the same pellet, it’s also very round and uniform. I think it shows that the factory barrel likes this pellet at power setting 10.

Talon SS rifle Premiers 25 yards power 10
On power setting 10, 10 Premiers made this nice round 0.329-inch group at 25 yards.

And JSB Jumbos at power setting 10 produced a group measuring 0.359vinches. That’s just slightly larger than the Premiers. I think the rifle really likes power setting 10. This group isn’t as round, but it’s clover-shaped, which is also good.

Talon SS rifle JSB Jumbo 25 yards power 10
Ten JSB Jumbos went into 0.359 inches at 25 yards.

Interpretation of these results
I will hold off interpreting the results of all the testing until I’ve shot the 1:22 barrel at 10 meters and 25 yards, but something stands out in today’s test. At power setting 6 and 25 yards, accuracy went out the window. It got better at the low end of the scale and again at the high end; but for both pellets, power setting 6 didn’t seem to work well at 25 yards. Yet, at 10 meters, that setting and JSB pellets produced the tightest group of the entire test.

This is the kind of thing an owner has to do with his rifle with each pellet he plans to shoot. And it’s also why spending an inordinate amount of time examining one specific power setting is useless if you don’t know the big picture first. Look at the JSB target on the zero setting at 10 meters to see what I’m saying.

58 thoughts on “How does rifling twist rate affect velocity and/or accuracy? Part 6

  1. Although the JSB 16.9gr. group was one of the best I have witnessed with a .22cal. airgun at 10 meters, we can’t reach any conclusions until the two other barrels are tested. If this test was being judged on accuracy alone, I would say you have found the right combination for your AirForce Talon. Test over. However, we have yet to see what the two other barrels do with the same pellets, distances, and power levels. When I think of the permutations one gun, three barrels, 2 pellets, and three power levels gives us, it puts this test firmly on a trail no one has yet dared tread. Who said there were no new frontiers to conquer? All it takes is a tenacious man who has the duel distinction of being a pretty fare shot with a good spectrum of shootin irons, and writing a first class airgun blog for one of the most eclectic group of aficionados I have been privileged to become acquainted. Using the old F.I.T.A. archery round of 144 scoring arrows, and 6 sighters, we find it takes the best part of a day. From 9.00am, till 4.00 p.m., with an hour for lunch, to complete a round. It was known as a round that tested endurance as much as accuracy, and separated the men from the boys. For you ladies, merely substitute the appropriate gender. So yes, I have a grasp of the time involved for shooting 120 Consistent (deliberate capital C) shots. Not only are you physically exhausted, but mentally drained as well. You have my complete attention with this test, and unflagging admiration to boot. Don’t forget to stop and smell the flowers that must be popping up in your neck of the woods. It is known to be a great therapeutic exercise. And don’t forget to pick a bouquet for Edith, who must wonder what she got herself in to. But that is a whole other test :-)
    Caio Titus



      • RR,

        What do you mean by that? I went to Part 5 and scanned it, and I can’t see how it applied to what Titus has said here.

        B.B.


        • Tom,
          TG said: “we can’t reach any conclusions until the two other barrels are tested.”

          It’s possible RR meant that the Quackenbush barrel has already been tested.

          -Chuckj


      • Thanks for picking that up, R.R. I should have qualified what I meant by saying “We can’t reach any conclusions until the Quackenbush 1.22 barrel has been fully tested too”. I keep telling myself not to write a response until I’ve had a good nights sleep. What looks fine at 1:00 a.m., can and does come back to bite you in the morning. Evan after a couple of proof reads. My Mother, who seemed to have a saying for any situation, would say that wars have been caused by a misplaced period. I never did find out if that was true, but I understand her meaning a bit better. At least our two countries are still friendly ;-)
        Caio Titus


    • Titus, that’s quite the feat of archery that reminds me of my thesis about the superiority of primitive man to the modern version. A book on this subject provided an example of some temple in Japan that has existed for centuries. There is an enclosed corridor of some hundreds of yards, and the challenge is to hit a target at the end of it. It’s not that difficult to do, but you’ll tire out and your arrows will start hitting the walls, floor and the ceiling. But there are records of some archers in earlier time who could hit the wall with fail for some ridiculous number of times. I believe there is even a zen exercise that is as much religious as practical whereby the archers should non-stop for 24 hours. Not rapid fire obviously but at some steady rate.

      Closer to home, there is the case of gun writer Bryce Towsley who procrastinated his assignment for testing a whole bunch of 12 gauge shotguns. He tried to do it all in a single day and ended up vomiting as the result of a concussion.

      Matt61


      • Yes, the F.I.T.A. ( Federation Internationale de Tir a L’arc ) round was one of my favourites. You have 6 sighter arrows at a 144cm. target face at 90 meters, and then shoot 36 arrows at each of four distances. 90, 70, 50, 30 meters for men, and 70 ,60, 50, 30, for women and juniors. A perfect score being 1440 points. When I was shooting in the early 80s, 1300 was the target score to achieve. The target decreases in size, to 80cm, at 50 and 30 meters. It was a round used exclusively in the Olympics, and World Championships. Although they have added an elimination round, to make it more exciting to watch, both at the venue, and for the television audience. The Women shot the shorter distance because it was thought they didn’t possess the strength necessary to pull a strong enough bow to shoot 90 meters. Add to this, the walking back and forth to score and retrieve your arrows, and it makes for a long day. If your shooting is off, it can seem like an eternity. It was at one of these tournaments, I first experienced what I would call a zen feeling. I was having a terrible time with holding my sight in the gold 10-9 ring. At 50 meters, it occurred to me to just hold my shot as long as I could, and let my hours of practise do the aiming for me. An amazing feeling of calm and assurance came over me. I tried to duplicate that feeling many times, until I realised it can’t be obtained by trying. It must be a subconscious act. This is serving me well with my habit of pulling the trigger with my airguns. Sorry for the wordy explanation. I have left a few details out, but I believe this covers the basics.
        One of the best books on the subject is Winner or Loser, by Shig Honda. He was the U.S.A.’s disabled archery coach in the 1980′s. I was fortunate to meet and talk briefly with him at the Las Vegas World Indoor Archery Shoot in 1983. Chapter 10 deals with The Realm of The Mind, and looks at the conscious, subconscious aspect of the sport. Another good book is Zen and the Art of Archery. Published in 1948, it documents Hugen Harrigel’s attempts at learning zen through the discipline of archery. It has spawned a whole bunch of Zen and the Art of books. One of my favourites being Zen and the Art of Motorcycle Maintenance. The funny part for me, is the use of zen to try and shoot better scores. Zen teaches to let go of all that deals with ego. Which is what competition is all about. Less is more.
        Caio Titus



  2. It is about time. I have been waiting a coon’s age for you to get back to this.

    I have been doing a little work with my .177 TSS and have about concluded that I either need to tune this thing down a bit or go up in caliber. They just do not make a heavy enough pellet for the valve setup on this thing. Even with an o-ring behind the top hat, anything under 12 gr that I have tried is still going supersonic. Maybe the H&N Barracuda Magnums will be on the market soon and I can give them a try. I also have another valve stem coming that might help tame it a bit also.

    Even so, I can see me picking up an 18″ .22 or .25 barrel for this thing soon.


    • RR,

      LEARNING HAS OCCURRED!

      I have written the same thing about a thousand times, but it takes the experience to drive the point home. You just don’t get all the power the Talon SS has to offer from a .177-caliber barrel. And a .22-caliber barrel can be just as accurate as a .177, no matter what the experts say.

      Good for you! :D

      B.B.



      • Well, now I’m going to have to get my .177 Talon SS out and see if I can get it to go supersonic. I use Crosman Premiers 10.5gr exclusively but I always shoot on the 2 setting since I only have 10m and don’t want to have to dig deep to extract pellets from my duct seal.

        Also, now I’m thinking I’m not giving Mr T a fair chance since I really have not tested the different settings for accuracy, which, apparently is the thing to do. I thought since I was whacking the targets so hard anyway, more power wouldn’t matter.

        So, okay, I may have learned something here, too. I’ll see.

        -Chuckj


        • chuckj…….

          I have been geting lower 800s out of mine with CPH. I set the power at 2. Fill 180 BAR.
          It is shooting at max power with that setup. A higher fill would require a higher setting . Probably 4 or 5 if I filled to max.
          If I go to .22, I have to do some adjusting to get the power up. It is a touchy rifle in .177.

          One time I did some adjusting with an 18″ barrel and got 1,000 fps with the heavies. PBA ran at 1200 fps, but were not impressive for accuracy.

          twotalon


          • Mine has a 26″ HW barrel and apparently a previous owner has bored the valve stem out to .2165″. Without the o_ring behind the top hat, I chronographed H&N Silver Points at 1240 FPS. That was when the hammer overcame valve lock at about 1800 PSI. Without the o_ring, it shoots Eunjins at well over 1000 FPS. With the o_ring, Eunjins and Skenko New Boy Seniors are just subsonic and shoot about 2 MOA at fifty yards. I hope to find a setup where I am averaging 1 MOA at that range.


          • twotalon,
            Here are my .177 TalonSS results trying to go supersonic:
            Chrony set up 20″ from muzzle
            2800lb charge (that’s all that’s left in my scuba tank)
            CrosmanPremier 10.5gr
            Setting # 2 – 358 fps
            Setting #4 – 575
            Setting #6 – 720
            Setting #8 – 887
            Setting #10 – 893
            Setting #7 – 886 (to see if tank was draining)
            Setting #12 – 888

            Hobby 7.0gr (Trying to so super)
            full tank recharge
            Setting #10 – 986 fps
            Setting #10 – 979
            Setting #10 – 976
            Setting #10 – 978
            Setting #10 – 969

            Try setting #12 for fun
            full tank recharge
            Crosman Premier – 891 fps
            Hobby – 979

            No supersonic for me. Come back next week.

            -Chuckj


            • Other than our power wheel settings, we get about the same velocity with CPH. Two different rifles, right ?
              Not going to try putting the short barrel in my Talondor. Running a 12″ .177 on a Condor power supply is probably going to dump the tank or blow out the endcap.

              twotalon


              • Twotalon,
                Right. Mine is stock .177 Talon SS. No mods at all, so, sounds like different rifles to me. BTW, mine is still very accurate at setting #4. On #3 I could tell a definite lag between gun report and target thwack. Also, setting #4 has a very low sounding report while #10 sounds much louder than my 10/22 Ruger rim fire.
                -Chuckj


                • chuckj..

                  The only thing I have done with mine that makes any power plant difference is to adjust the tophat. In stock condition it was sucking air really bad. The tophat and power wheel adjustments helped a lot with air usage. Not nearly as wasteful.

                  twotalon


                  • I tried adjusting the power wheel and all I accomplished was chasing valve lock. I adjusted my pw to six and after about six or seven shots they were ss again. The pressure was at 1600. I turned it down to four and again, after a few shots it was ss with the pressure at 1400. Turned the pw to two and the same thing happened when the pressure dropped to 1200.

                    I figure I will get a regulator set to 1800 PSI, get a stem with a smaller port, fill my tank to 3000 PSI and shoot all day.



  3. BB,
    Looking good, and interesting as well. The 1:22 should tell the tale at 25 yards, any ETA on that test? I’m biting my tongue to keep from making predictions, esp. on the 50, but I’m starting to imagine a pattern to the data… Of course, more actual test data could make me go back to the drawing board :)!


    • BG_Farmer,

      Hopefully I will do the 1:22 barrel test sooner than I did this one. The 50-yard test will take 3 trips to the range, as the barrel has to be changed. I might be able to do it in two trips if the wind cooperates, but I need a calm day to really test right.

      I will summarize after the 1:22 test at 25 yards and again at the end of the 50-yard test.

      I’m planning on not shooting zero power at 50 yards, only because it takes more time and the delta between that and powers 6 & 10 is so great at 50 yards.

      B.B.


  4. B.B.

    All right, a bigger picture lurks somewhere very near. Time to brush up on my math and draw some lines and tables. I must confess I already made some predictions for myself, but theory is always dead unless there’s some live data and math has always been my weak spot.
    I also wonder what results could be produced with some sort of shooting robot, not B.B.’s magic hands – it could be called a scientific cheating.

    I don’t want to scare my luck, but I seem get close to some very interesting findings on my rifle. It may be the way it’s being held in place inside stock that affect accuracy – but I must first test it in test stock mockup before making any conclusions.

    duskwight


    • duskwight,

      I can “hear” your unspoken questions about bedding in what you write. Yes, bedding may be your problem. If you think it is, look at what firearm makers do to bed their guns, and try to do that if you can.

      B.B.


  5. My analysis is that those are some fine groups. Sub-minute with the Talon by a considerable margin. I would venture to say as much as a .7 MOA 5 shot equivalent in some cases. As for the experiment, it would help me to figure out which are the dependent and independent variables here. As I read it, the twist rate is the independent variable. So you vary the twist rate and examine the effect on velocity and accuracy as the dependent variables. If we’re changing the velocity too by means of the power setting, that introduces complications.

    Herb, yes, the dampening effect of air resistance on bullet stability is an interesting and paradoxical effect since air resistance is generally taken to retard accuracy by slowing bullets down, forcing a trajectory into the bullet’s path and generally working against desired values for the ballistic coefficient. But to claim that bullet stabilization can improve long-distance accuracy bumps us back to our discussion of spiraling projectiles. As I understood it, there are a couple things in the way of making this connection. The first is that the spiral of the bullet (projectile) has to be responsible for (mapped directly onto) a significant fraction of group size. The difficulty with this is that it doesn’t scale upwards. For people to attribute variation in group size–as well as certain clockwise progressions of impact points–at shorter distances to spiraling implies that the bullet will be spiraling around some ridiculous diameter farther out.

    Bullets do spiral as many have seen. But either the spiral takes place at some long distance when the projectile has completely lost stability and cannot make a group. Or, during the stable phase, the movement of the pellet is contained within a smooth and predictable arc. So, again the precessing movement of the projectile nose is not tied directly to projectile path; it takes place within this path.

    If the spiraling is detached from group size then it can’t very well contribute to increased accuracy at long-range. Once the pellet gets its act together and stabilizes it will have lost all memory of where the target is and be unable to move back. Besides once a sideways component of motion is imparted. Physics said that it can only be reversed by some new force. So while a stabilization of the bullet can reduce further aberrations, it cannot make up for ground that has already been lost. So, practically, your MOA as you move out can reduce its rate of increase but it cannot shrink.

    Victor, that is a very interesting point that even the great ones can break. It’s said that mental or emotional disability is really a spectrum disorder which only becomes pathological where it becomes seriously disabling in a sustained way, but there is no one who escapes. In rowing, the wisdom was that everyone has a breaking point, even at the elite national level. It’s just a matter of where and when it’s going to happen. On this subject, one of the torchbearers at the London Olympics was Sir Steve Redgrave, rowing god of Britain, who has been in some ridiculous number of Olympics with an endless list of medals. But I remember reading about him some years ago when he was already famous. He was matched up in a single scull against an unknown fellow from Denmark, and it was expected that Redgrave would dominate. The unknown started out strong, and everyone looked for Redgrave to row him down. But he didn’t. They moved down the course and the unknown stayed ahead. Redgrave started losing ground. Then around one bend, he was seen to have stopped rowing altogether. He just up and quit on a big stage. Afterwards in an interview, he said, “I am sick of myself.” The scoreboard said in British style, “Not rowed out.” Ouch. But he pulled it together and ultimately had a happy ending as can be seen with the London Olympics. Yet another object lesson not to dwell on the past but to look forward.

    I seem to have found myself in the two most restrictive states for gun laws in the entire country. California was talking about surpassing New York and resuming pride of place as the most restrictive state of all. Some have talked about modifying semiauto weapons so that they can only be fired one round at a time without some intervention. Now there is a movement to ban all lead ammo. I’m not going to hold my breath for the non-lead 8 mm Mauser to come out. And what’s going to happen to my thousands of .22 LR that are stockpiled? I wonder if this will affect my airgunning too so that I can’t even shoot lead pellets at my home.

    Hawaii may not be an escape. Some state senators have introduced bills to not only ban semiauto guns but require owners to surrender them. There will be no grandfather clause. And there are other things like yearly re-registration of guns, background checks for ammo, and background checks for everyone living in a home with a gun. Hawaii is an interesting case. It’s basic outlook is extremely liberal with a long history of labor unions who were formed to stop the abuses of plantation owners on immigrant workers. However, there is an intensely conservative strain with the enormous military presence and the record of the 442nd Regimental Combat Team, the most decorated unit of the U.S. military in World War II that was composed of Japanese Americans. Almost all the weapons on the massively overcrowded public rifle range are AR-15s. Anyway, the federal legislation would be mild in comparison with what is proposed here.

    Matt61


    • You need to get out of the Peoples Republic of Kalifornia!

      “You may all go to h—, and I will go to Texas!”
      Davy Crockett


  6. “In the world of testing, what I’ve done is called a quick look ” Well Tom, that was a long ‘quick look’.
    Thanks for all your hard work, it’s much appreciated, with some interesting results.
    Good luck, Phil :-)


  7. Matt61,

    Real champions experience setbacks from time-to-time, but never defeat. The mind of a champion knows that time is their friend. The champion may feel a little pain now and then, but they are never discouraged. Champions are optimist, and no one can make them doubt themselves. While they may not be able to master everything, they certainly do know how to try and do their very best. Ultimately, that’s how you define a winner.

    Victor


  8. Going a bit off subject. Today I was watching the senate Judiciary commitee hearing on Feinstein’s gun debate where she insisted that Adam Lanza’s Bushmaster that was found in the trunk of his car after he had killed himself was responsible for dismembering the children he shot. She then went on to say she saw bullets implode. So I have to ask this. I know a gun like the Bushmaster cannot dismember anybody, but can anybody think of a way to make a bullet (or pellet) implode? How would that work? Or did I just hear Diane Feinstein flat out lie to push her gun ban today?


  9. Imploding bullets are the ones that collapse upon themselves, turning into teeny-tiny black holes in the process (just like Ms. Feistein’s br…. oh, never mind).

    It’s a big problem. I believe she should introduce a bill to ban imploding bullets. I suspect even the NRA wouldn’t object.


  10. B.B., I don’t know if anyone else has asked you before, but why do you almost always
    use the 1962 dime and not another coin of another date?



    • Kevin,

      of course what BB wrote is a very funny story but I would like to take the blame or credit, as Tom see’s fit. After he found that dime in circulation one day and mentioned it in a blog, I suggested that he continue to use it in all his photos. You see, it’s pure silver – not a plated or sandwiched coin the way all our coins are today.

      BB? Care to add or correct me?

      Fred DPRoNJ


      • Fred,

        You won’t believe it, but three weeks ago I found an almost uncirculated 1937-S buffalo nickel in my change at the local Chinese restaurant. Obviously someone raided a coin collection, but how neat is that? :D

        B.B.


        • That nickel could be worth as much as $15 depending on condition but I’m sure you know that. Afterall, you used to be a rare coin dealer in NY :)

          Congratulations. Not sure why stuff like this never happens to me.

          Fred DPRoNJ


  11. I hope someone can answer my questions:
    The .22 Stealth (very similar to Talon SS) can take air tank from .177 and .22 guns. Will I get more muzzle energy from .22 pellet shooting out of a .22 gun using a .177 air tank (compared to the original .22 tank)? my intuition says there shouldn’t been any difference. but someone says it matters. can any expert help?

    If both guns are set for a fixed muzzle energy, say, 10 ft lb. Knowing that .22 pellet is about twice the weight of .177, the velocity of the .177 guns must be higher (about 1.414 x) than that coming out from the .22 gun (E = 1/2 M*V*V) to give the same energy . But does it means that more air will come from the tank of .177 ?


    • Too many variables to state one way or another….

      14.3gr, 10ft-lbs, 561fps
      7.9gr, 10ft-lbs, 755fps

      But will it use more air? Remember, the volume of the bore is much smaller, so a given amount of air will be at a higher pressure as the pellet reaches the end. 18″ barrel

      .22 x 18″ => 0.684 ci
      .177 x 18″ => 0.443 ci

      Is that pressure differential sufficient to achieve the higher velocity? Will the back-pressure actually hold the valve open longer?


  12. Thanks for your prompt response.

    So if I have a gun with interchanging barrel, will there be any change in muzzle energy between shooting shooting .177 and .22, using the same air tank?



  13. I don’t understand how you measured the group sizes, look at the JSB Jumbo (0.10 inch) group, it’s much bigger and can’t be 0.1″=2.54 mm between the centres… Can you enlighten this to me please?


    • maestro,

      To measure the distance between the centers of the two widest shots in any group, measure from the outside of one hole to the outside of the other hole (of the two holes farthest apart) and subtract the diameter of the pellet.

      B.B.


  14. Just have a look at the 2nd (JSB Jumbo) image, it can’t be 0.1″ CTC. Maybe it would be worth to double check your measurements.
    And if you accept an advice, don’t forget that the holes are smaller than the pellets, I’d use rather the centres, it’s easy to align a circle onto the photos in a CAD software and measure the CTC distances then.
    Please have a look at the following picture:





      • Maestro,

        I reconsidered your comments and looked at your phot again. The mistake you made is in drawing your pellet circles in the wrong place. That’s why your measurements are in error.

        Paper targets don’t always tear the same way every time, and because you don’t have the original holes to examine, you can’t make the measurements accurately.

        Your holes on the 0.10″ group and half a radius off-center!

        That’s what I mean by your perspective being off.

        B.B.


  15. I can work only from your photographs but even if I move the circles to the hole edges, the distance of the centre points is still 0.17″ (assuming that you have used the standard ISSF air rifle target where one ring width is 2.5 mm). And if you look at the left side of my picture, those two circles are really good visible and the distance is 0.58″ in my calculations. All I ask is to check your results one more time, you have done a great work but I can’t believe these group sizes…
    P.S. Please remember our last debate in 2007 about high scope vs. canting, I just would like to help you mate :-)


    • maestro,

      Take some time and read the caption for the group that measures 0.092″. You’ll see that I said the paper closed back around the pellet hole, so the measurement was larger than it appeared in the photo. I didn’t bother to explain that the group you are complaining about also tore incorrectly too, but it did.

      I have measured that group a second time and that’s all I’m going to do. You cannot take photos from the internet and measure them accurately, because they have been scaled differently when they are transferred from digital images to the reduced-scale image on the web. You can do gross interpretations, such as determining that one is larger than another, but you can’t use a micrometer on pixels.

      B.B.


  16. BB, I’m an engineer and have scaled the pictures by the known sizes of the target rings with a professional CAD software. But I think it’s better to quit now, it’s been a pleasure to chat with you again.


    • maestro,

      While you scaled the images, keep in mind the resolution and enlarge/reduce on each person’s browser is variable. What you see is not necessarily what I see, B.B. sees or anyone else sees.

      Edith


  17. Dear Edith, you seem to forget that I’m an experienced CAD user. When I say that I have scaled the images then you can be sure that they had real sizes in my 2D window, e.g. the bullseye was 60.5 mm etc. Never mind, also the high scope topic had inspired me to write a detailed article about the question, maybe I’m gonna write next time about the precise method of measuring shot groups LOL


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