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7-1/2s or 8s at 42 yards.

Discussion in 'Shooting Related Threads' started by Dr A C Jones, Mar 21, 2010.

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  1. Dr A C Jones

    Dr A C Jones Member

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    7.5s versus 8s, hey, that old nugget. Answering this is something that has been bugging me for a while. Actually, it's more a sporting clays scenario I have been thinking about. UK rules allow up to UK#6 (US #6.5) sized pellets (but only 28g/1oz). I sometimes use UK #6.5s because I can use them against feather or clay. They seem to work OK on clays but I already know that you can't tell much by "reading the breaks". Is it worth using the big stuff?


    A little post-amble preamble: If a solid slug were used against a clay pigeon, it should be obvious that wherever the slug hit on the clay, the clay will break. The downside, also obvious, is that there would be a low probability of hitting the clay. At the other extreme, #10.5 shot that the Italians apparently use to blast songbirds would hit the target every time but bounce off the clay pigeon (assuming some distant target). Somewhere between these two extremes is the optimum balance of pellet count and target breaking effectiveness.


    An obvious point from the above: One pellet of sufficient size/energy is able to break a clay pigeon. You don't need an in-depth understanding of anything to realise this. If you can't accept this don't bother writing here about it. The only debate is how large/energetic the pellet needs to be to break the target (almost) every time.


    There's actually a refinement to that last paragraph. Not only must the pellet have sufficient energy, but it must also strike at a favourable direction or position. The more energetic the pellet, the more of the clay pigeon that is vulnerable to the pellet strikes.


    What I have been working on in the Bat Cave is a model of a clay pigeon and its susceptibility to pellet strikes. There are more than a few assumptions along the way and a little "calibration" is needed to improve accuracy, but as it is, things are quite interesting . . . .


    [​IMG]


    The graph shows the probability of a clay breaking for a range of assumptions. Because overall effectiveness is a function of pattern density and pellet energy, a distance and pattern spread must be defined. In this case 42 yards, 1300 fps muzzle velocity, and a pattern spread equivalent to 72.5% PE. The probability figures of hitting/breaking the target are restricted to the centre 5" of the pattern.


    The "White diamond" trace in the graph is the probability that pellets will strike the target based on the pellet count and target size alone, i.e. no allowance is made for pellet energy. It is what I have used in the past to calculate the probability of pellets striking a target. The graph shows increasing pellet count increases the probability of the target being hit. Note that with typical pellet counts used in trap, the probability of hitting the target is less than 100%. This drops further with 1oz loads.


    At the other extreme is the solid black line. This assumes a pellet energy capable of breaking the target 100% of the time. Different threshold energies needed to break the clay pigeon are applied to different areas of the clay pigeon. The steps in the response are where different regions become impervious to lower energy pellet strikes.


    The dotted line assumes lower energy thresholds for certain areas of the clay pigeon. Consequently, pellets are more likely to break the target. The dash-line uses the same data from the dot line, but assumes that the pellets are only effective 90% of the time, i.e. some of the time multiple pellet strikes are needed. This is not inconsistent with the earlier assertion that only one pellet is needed.


    So, conclusion time:


    The energy needed to break a clay pigeon has a big effect on the overall chance of a target breaking. I assumed an ISU style target. I have been told that US targets are weaker. This makes a big difference and could lift the curves in the graph by one-ish percent.


    More muzzle velocity = more down range energy = more chance that any pellets striking the target will break it. Excepting the effects of recoil, hot loads are superior.


    Changing pellet size by +/- one step doesn't make much difference. This is good because shell/shot makers generally do a poor job of putting the expected size shot in the packet.


    For the range of assumptions made, in the range of shot sizes typically used by trap shooters giving a pellet count of 400-500 in 1-1/8 oz, shot size makes at most 1% difference to the chance of breaking the target assuming the pattern is perfectly placed.


    Note that the dash-line and solid line peak at ~95%. Looking at the top shooters at 27-yard ATA trap, their averages are ~95%. It's not exactly coincidence because I used knowledge of the averages to justify some internal assumptions. However, what it does suggest is, the idea that top shooters are handicapped by ballistics, not the difficulty of the discipline (assuming they break the targets at 42 yards).


    To do better than the figures suggested above requires tighter patterns or more energetic pellets. Both of these follow naturally from shooting faster. That the top shooters get an average of ~95% and sometimes do a lot better suggests that a number of the shots are taken before 42 yards. All the curves move-up if the target is shot sooner. A couple of yards makes a big difference.


    7.5s or 8s? If 42 yards is your target distance I would recommend 7.5s. The shot is often under size and the graphs suggest things go down hill rapidly with shot that is too small. Slightly over-sized shot may help, but otherwise will suffer only modest decline in overall performance.


    If you can shoot quicker, I need to work out the graph again. It can't be scaled easily by hand because the underlying models are highly non-linear.


    Another obvious thing should be that the subject is very complicated. A few boxes of complimentary shells shot off at some complimentary targets is not a very good test of how good a shell is. Bear that in mind next time you read a cartridge test.


    I realise that the skeptical will have picked-up on my liberal use of the word "assumption". The assumptions are not picked out of thin air, they are engineering assumptions or tentative deductions from measurements. For the most part they don't affect the relative results such as pellet size does not make much difference. They do affect the absolute level, i.e. is the peak 95% or 97%. I'm not sharing the assumptions or models yet, as beautiful as the equations are (at least to a mathematician).


    Andrew.
     
  2. 4th. down

    4th. down Active Member

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    Thanks, AC. This will become more interesting as time passes, on this forum. However, for now, does anyone know how many fps. you lose @ 3' velocity measurements compared to muzzle velocity?
     
  3. Pocatello

    Pocatello Active Member

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    Andrew, interesting reading, as always. I'm particularly struck by your statement about targets: "The energy needed to break a clay pigeon has a big effect on the overall chance of a target breaking. I assumed an ISU style target. I have been told that US targets are weaker. This makes a big difference and could lift the curves in the graph by one-ish percent."

    I had a meeting to attend this weekend at Walla Walla, Washington. The meeting was held in conjunction with a fairly large shoot. I may be wrong on this (and someone please correct me if I am), but I believe the targets being thrown were Caldwells, a brand with a reputation of being harder to break than the White Flyers more commonly used. The reason I believe the targets were Caldwells was that I saw a Caldwell truck on the grounds, and heard several people state that Caldwells were the brand used. I did not examine any of the targets or target boxes. In any event the scores I saw at the shoot were significantly lower than I would expect for a shoot that size. In Friday's handicap 95 was the high. Stu Welton, who last year set the all-time ATA average record for a year, broke about 94 in the doubles, 99 in the singles, and 91 in the handicap. The shoot management was short of help Saturday morning in the singles, so I volunteered to score for them. I watched one squad of good shooters I know shoot 50 rounds each, then scored another four full squads for fifty rounds each. That's 50 lines of 25 targets each from 16 yards. There was not one 25-straight in those 50 lines. In the targets I scored there were a fair number of unbroken targets that gave off fairly heavy dust, indicating a strike by at least one pellet, but only one of those had a visible piece come off, and that piece appeared to be much less than 5 mm in diameter. In that Singles event with over 200 shooters entered there was one lone 100 straight, and not many 99s. Clearly those targets were tough to break, and perhaps one pellet was often not enough to break the target.
     
  4. Ajax

    Ajax Well-Known Member

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    Pocatello, evidently you didn't read the whole thing? I think you missed the part where if you don't accept the one pellet break theory, Doc. doesn't want to hear about it in this thread. LOL

    Ajax
     
  5. zzt

    zzt Well-Known Member

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    Dr. Jones, what were your retained energy assumptions for the different areas of the target?
     
  6. Dr A C Jones

    Dr A C Jones Member

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    Thanks for that Ajax. Pocatello, you do accept that if they had used #6s then the whiffs of dust would have been breaks?


    The picture below is from the "reading the breaks quiz". It shows a pellet strike that does not break the target. It was a high velocity UK#7.5 with a target at approx 35yds. I have never stated nor assumed that every pellet strike breaks the target, only that a pellet strike of sufficient energy will break the target (almost) every time.


    The question is, does using bigger pellets convert more of the puffs of dust into breaks than it loses due to lower pellet density? Instinctively, I'm leaning towards the larger pellets. I'm actually more comfortable with the solid black line in the graph above, but this is inconsistent with the known scores from ATA unless they shoot a little before 42 yards. If they do, that peak at 370 pellets moves towards the 400 pellet mark which is a legal pellet size. There are still a lot of imponderables, the most significant in this case is the target break distance.


    Andrew.


    [​IMG]
     
  7. Dr A C Jones

    Dr A C Jones Member

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    zzt, I'm not disclosing that or the discretization of the target at the moment. If it was college work it would be worth a PhD thesis.


    One thing I have noticed is that the susceptibility of clay pigeons to pellet strikes is likely to be very different from supplier to supplier. Some of them add design features to (I suppose) aid breaking, but it probably achieves the opposite. Some features aid breaking at some presentation angles but hinder at others. This is why for Olympic Trap and sporting clays it is probably impossible to "tune" the pellet size to the target. On average the curves in the graph above would tend to be much flatter because the "gain a bit, lose a bit" effect of changing pellet sizes is smeared over the many different scenarios.


    It seems like a major oversight to me that size and weight of clay pigeons are specified but not frangibility.


    Here's another thing to make you think. Target spin speed (also included in my calculations) affects the probability of the clay breaking. Places that throw lazy targets thinking it makes things easier, are actually making the target more difficult to break; easier to hit, but more difficult to break. Again, there's a "gain a bit, lose a bit" effect. You can lose a lot if the clay skids off the arm of the trap rather than rolls down it.


    Andrew.
     
  8. Setterman

    Setterman Well-Known Member

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    I figured Neil would be all over this one! Did he and Dr. compare graphs before this was posted?
     
  9. Pocatello

    Pocatello Active Member

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    Ajax and Dr. Jones, I do accept the statement "One pellet of sufficient size/energy is able to break a clay pigeon." What I was trying to illustrate was your point that different targets may take larger pellets/more pellet energy to accomplish the break. I do assume that you agree that a target that gives off dust but no visible piece has been struck by at least one pellet, but has not "broken" according to the rules we play by. I was just trying to illustrate that your statement "One thing I have noticed is that the susceptibility of clay pigeons to pellet strikes is likely to be very different from supplier to supplier." sure seemed to be the case at the Camas Prairie shoot last weekend, as evidenced by the scores. In particular fifty rounds of twenty-five singles targets without one twenty-five straight, and more than a few targets giving off heavy dust but no chips seems to be good evidence of a target harder to break than the usual White Flyers I see.

    I think that anyone who has ever looked at patterns, especially those shot at distances typical for target breaks at 27-yard handicap, would doubt that many, if not most, of those targets are broken by single-pellet strikes. The patterns are just too disperse to believe otherwise.
     
  10. gdbabin

    gdbabin TS Member

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    Dr. Jones,


    I don't see evidence from the picture alone that the target was actually hit. You could certainly make that deduction; however, it's also possible the shot cloud passed either in front or behind the pictured target.


    It is a cool picture though. A video might have been more revealing giving an indication of any deflection which would have accompanied a hit.


    Guy Babin
     
  11. spitter

    spitter Well-Known Member TS Supporters

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    Doc... at that distance I use a #7 steel loaded to 1300 fps...

    regards,

    Jay
     
  12. porky

    porky TS Member

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    Dr. Jones In order to break a clay target,I have noticed that the clay target design requires a strike of pellet or pellets at the bottom of the clay target and not at the top. The dome is suceptable to punctures by individual pellets and not break a piece off of the clay target. On the bottom, the thicker,launching area, in hit with a pellet(s) will generally break a small piece of the clay target off. That is the reason, I believe, that people are able to see dusting of targets as well as locating targets on the ground with holes in the dome part and still have the integrity to be reused. If a club uses all orange targets, small pieces can be seen far more easily than if the small piece is from a black portion of the target or a light colored target,ie lime or white,etc. This is dependinding on background, of course, but is applicable at most clubs.
     
  13. yansica1

    yansica1 Member

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    Hi Doc, Now I don`t really want to get dragged too deep into your graph games but half a lifetimes worth of actually shooting as opposed to drawing and contemplating things has taught me a few things that may be of benefit to your cause particularly as we both live on the same side of the pond.

    I agree that a single pellet strike at normal target distances, will result in breaks almost everytime. I personally use English 8`s (2.2mm) for 95%+ of my shooting and would say that the benefits of throwing 45 extra pellets targetwards each time is easily countered by any probable difference in breaking capability between that and 7.5`s which don`t forget are 2.3 mm which is hardly any real increase particularly so as you`ve noted that there are indeed shot size variances in shells in any case.

    One interesting thing I find is that when I started back in the early 80`s there were many more instances where shot could be heard tingling and bouncing off targets without breaking them, nowadays it is almost unheard of. The possible causes are many; for instance we tend to shoot tighter chokes nowadays and the skill levels are also better, pellets are arguably harder, in the olden days they probably used the same shot from the game loads to load the clay fodder? But it is likely that clay manufacturers have the most to do with this.

    PS. since you are so close relatively speaking, don`t you think that you owe it to yourself to take up my offer of making a believer out of you when it comes to reading breaks? Afterall for one so interested in the mystique of shots and patterns you sure are missing a trick. Paper and reality are not one and the same. Good luck.
     
  14. Neil Winston

    Neil Winston Well-Known Member

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    No one who used to hear "tinkling and bouncing off targets without breaking them" can do that any more I think we can all agree. But the answer is not to be found in the targets, but rather in the fact that those who could hear it were using such inadequate ear protection they can't hear much of anythng anymore.

    Neil
     
  15. perga1

    perga1 Active Member

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    You're right Neil. Jim
     
  16. Paladin

    Paladin Well-Known Member

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    Is it legal to use 1 1/16 oz of 8's at say 1300 fps? Or would 1 1/16 oz be technically classified as larger than 1 oz, therefore limited to 1290 max? The rule book does not specifically address it.
     
  17. Neil Winston

    Neil Winston Well-Known Member

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    Yes it does. It forbids

    "3. Any load with a velocity greater than 1290 FPS (Feet Per Second)
    with maximum shot charge of 1 1/8 ounces, or 1325 FPS with a
    maximum shot charge of 1 ounce,". . .

    Neil
     
  18. Paladin

    Paladin Well-Known Member

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    Thanks Neil. I stand corrected. I've shot a fair amount of 1 1/16 at everything but handicap, and obviously at lower velocities. (What took you so long to reply? Had to look it up, didn't you? LOL)
     
  19. Neil Winston

    Neil Winston Well-Known Member

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    I think about everyone who shoots shells reloaded with an unmodified MEC 5118 bar is shooting 1 1/16 oz, Paladin.

    But we did have to make a wording change a couple of years ago to address just such a question. People wanted to shoot "international" loads and so wanted more speed. But if you look in reloading guides, you will see all sorts of confusion as to what that means. So we just added the two words "or less" and now it reads

    "or 1350 FPS with a maximum shot charge of 7/8 ounces or less,"

    and now that question has an answer too.

    Neil
     
  20. Sportshot

    Sportshot Active Member

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    nevermind....
     
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