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POI

Discussion in 'Shooting Related Threads' started by djpk69, Feb 28, 2009.

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  1. djpk69

    djpk69 TS Member

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    I have a SKB 85 TSS Unsingle that I shoot fairly WELL. I just bought a SKB (YES,I'm a SKB fan) GC7 Topsingle. both have a MC Adj. stock (my new GC7 is left-handed ,as I am). IF, I go to the pattern board with the idea of "getting" my new gun to shoot where my old one does,where should I shoot from ??? 13yds with a trap full?? That's my thinking, then I can match the two?
     
  2. djpk69

    djpk69 TS Member

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    THANKS JOE...BTW...my BT100 is for sale at Jaquas. As is my BPS trap/and 1st trap gun (a BSA O/U). Might break EVEN ! But.....better to BREAK some CLAYS !
     
  3. djpk69

    djpk69 TS Member

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    These are my 2 SKB's
     
  4. hmb

    hmb Well-Known Member

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    You will have to make an allowence of a couple inches at 13 yards because one barrel is an unsingle and the other is a top single. To be the same the top single should pattern a little higher at 13 yards. To get the exact distance measure the difference between the height of the barrels in relation to the rib and multiply by .783426971289. HMB
     
  5. djpk69

    djpk69 TS Member

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    Thanks HMB..that would possibly explain my discrepancy. I had to move my new comb left about 3/16" to be centered vertically. But moved it up 3 spacers to get horizontal.I think I need to go back down now. So, if my topsingle barrel is 1" higher than my unsingle, multipy that X .783426971289 would be roughly 7/8" ??
     
  6. djpk69

    djpk69 TS Member

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    HMB, if that is true, I went the wrong way......again. And, I can't raise my topsingle any farther?
     
  7. zzt

    zzt Well-Known Member

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    dkunser, you should check the choke tubes that came with your new gun to make sure they shoot to the same POI. You would be amazed at how many don't.
     
  8. phirel

    phirel TS Member

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    dkusner- HMB was making a little fun at some of us who like numbers. We deserve it. Ignore his coefficient. He actually intended you to ignore it.

    When I extrapolate the POI at 13 yards to 40 yards, I do calculate the distance from the center of the bore to the front sight and multiply this distance times 2. I also factor in a 2 inch drop due to gravity. I like numbers.

    You can do just as well by ignoring these things. If your old gun shoots 3 inches high at 13 yards and you get your new gun to shoot the same, you are set.

    Pat Ireland

    PS 7/8 inch = 0.8750 inches
     
  9. djpk69

    djpk69 TS Member

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    ZZT, both my SKB's use the same Briley Competition tubes. I used the exact same one in both.Pat or anyone... The difference between center of bores to front sights is about an INCH.Both now shoot the same at 13yds. What do I have to do to get them shooting the same at 40 Yds??? I don't want to change my unsingle as Tom Smith fitted it 3 years ago and I touch NOTHING but Pads from Winter to Summer.Am I correct that my Topsingle needs it's comb raised now..what other options as I am out of room to go UP anymore ?? New posts ? Soft comb added ? or add on rib ?
     
  10. hmb

    hmb Well-Known Member

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    Using the same tube in both guns seems like a good idea, but there could be a problem. If the tube is a little off center it would only act the same in both guns if when tight in the barrel it was oriented the same way. You could put a little mark on the edge of the tube so when you tighten it in each barrel you can check the orientation. If when tight the mark is in the same place, for example 12 o'clock, for both barrels, then you would be good to go. HMB
     
  11. zzt

    zzt Well-Known Member

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    dkunser, if your top single shoots about 7/8 inch higher than your unsingle does at 13 yards, they will have the same POI at 40 yards. The trajectories are different, and that is magnified at 13 yards. Also, you really need to do this standing like you do at the line, not from a rest. If you are like me, the top single will rotate upwards a little more in recoil, and that affects POI.

    For what you are trying to do, I find 20 yards and a grease plate the best setup. 30 yards is OK with a tight choke. At these distances you can still easily determine the center of the pattern, and you don't have to worry about correcting for anomalies when shooting at 13 yards.
     
  12. phirel

    phirel TS Member

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    dkusner- If they shoot the same at 13 yards, they will shoot the same at 40 yards.

    zzt did raise an important point. Measuring the POI only tells you where the gun shoots. It does not tell you where you shoot the gun. That is more difficult to figure out.

    If you want to raise your comb more, it will require longer posts or the addition of something on top of your comb.

    Pat Ireland
     
  13. djpk69

    djpk69 TS Member

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    I guess I'll try the little " nick" thing on the same choke tube this week and shoot without a rest from 40 yards. What was really stupid was that 3 of us determined that, for a left-hander,the comb's horizontal movement is reversed. My pattern was left so I moved the comb left .......twice....till I was centered(I must have mis-shot or subconsciously pulled the barrel right). Something didn't seem right, as I bought a LH topsingle, and now my comb was way left. I only broke a 17 and a 15. I got to analyzing this and determined that left is left and right is right for a Lefty also. It took holding a pencil to my left check and watching the front of it go right as I simulated moving the comb to the right . The 3 "STOOGES". Comb's and Transits are not my forte'.My last resort will be to go back to Tom Smith and get this gun shooting where I'm looking.But, I'm determined to save $150 and finally get this figured out.

    ZZT and Pat,who is right? Pat says "if they shoot the same at 13 yds,they will shot the same at 40yds" ZZT says " if the topsingle shoots 7/8" higher than your unsingle at 13 yds,they will have the same POI at 40 yds" ???
     
  14. Neil Winston

    Neil Winston Well-Known Member

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    Pat, you wrote earlier

    "PS 7/8 inch = 0.8750 inches"

    and this is not strictly true. Yes, 7/8 is 0.875 but 7/8 inch is a range from 0.8125 to 0.9375 inches.

    Neil
     
  15. hmb

    hmb Well-Known Member

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    Please explain yourself Neil. I believe Pat has sufficient cranial capacity to know what 7/8 of an inch is. HMB
     
  16. Neil Winston

    Neil Winston Well-Known Member

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    I did.

    Neil
     
  17. djpk69

    djpk69 TS Member

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    So, who is right ZZT or Pat ? OR...both ?
     
  18. zzt

    zzt Well-Known Member

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    dkunser, Pat and I are both right. Pat likes round numbers, while I'm a little more precise. Don't worry about it. Either way you are going to be very close at 40 yards, certainly within 2". You are going to do your fine tuning while actually shooting birds anyway, so just get it as close as you can, then go shoot targets.

    Put a tight choke in your top single, set the trap for straightaways and shoot and adjust until you are smashing birds just like you do with your unsingle. Then try the other posts. You may end up having to adjust by 1/32" or even 1/16". When you are happy with the results, go back and shoot POI at 13 again, for the record. Chances are it is not the same POI as your unsingle (it will be close). Don't worry about it. You have just proven they are the same at 40 yards by shooting. So record the results and forget about them until you fiddled or experimented and want to get back to square one.

    Added after the fact: after you've done this, I'll bet you a soda your TS POI will print .6" higher than your US @ 13 yards.
     
  19. Neil Winston

    Neil Winston Well-Known Member

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    Both, for all practical purposes. I'm not so sure - even doubtful - about that greater rotation of an over-single and in particular I don't know how you could test it. I also think that greater precision than a couple of inches is unrealistic, which is why I said for all practical purposes.

    The thing is, you never have to worry about the 40-yard POI anyway. Any place you test it, if it's the same, it's the same. The converse is also true, of course.

    I also favor the use of a benchrest and doubt results reported as obtained by any other method are anywhere near as repeatable, but that you can test for yourself. Just do it from 13 yards with maybe a dozen shots each way and see how it comes out.

    Neil
     
  20. phirel

    phirel TS Member

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    Neil, ZZT and I are all correct, but with slightly different answers. My position involves the level of significance. I believe it is inaccurate to measure anything to a greater precision than it can be accurately measured.

    Example- if zzt were to report the standard deviation of 2.12,1.88,2.98 and 1.98, he might state it is 0.5031. Neil might say it is 0.50 and I would conclude, based on sample size, the standard deviation is 0.5. Then the three of us could have an entertaining discussion about who is most accurate. But, the fun the three of us could have would soon be spoiled by Pacatello who would be able to give the correct answer. Pocatello knows numbers. He has a PhD in statistics. ZZT uses numbers. He is an engineer. But Neil and I only play with numbers for fun.

    Pat Ireland
     
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