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Rollin Oswald is dead on - of course

Discussion in 'Shooting Related Threads' started by GrandpasArms, Sep 4, 2012.

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  1. GrandpasArms

    GrandpasArms Active Member

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    Reference page 180 of Mr. Oswald's "Stock Fitter's Bible". I got time to pattern my BT99 at 35 yards this weekend. It's a grease board and colored black.

    I set the BT99 (fixed full and 34") stock as low as it went and found my horizontal is dead on and my vertical center is one inch or so (This meshes with reports that the older BT99s shot flat). I should note that the adjustable stock was added and doesn't go all the way down.

    I then added 1/4 inch to the comb (back up to where I had been shooting it). According to Rollin Oswald's book, that increase should push the POI up 7.15 inches. I placed a shot at 35 yards and measured 8.25 inches to the center (7.15 + 1 = 8.15 and I measured 8.25). I did it another 5 times (6 altogether) and they were all in that same place - 8.00 to 8.5 inches. Son of a gun. The math works just as it should.

    Larry Frieders
     
  2. Scott Johnson

    Scott Johnson Well-Known Member

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    And Rollin is very heplful in responding to a shooters gunfit challenges. He is good people. Scott
     
  3. Calkidd

    Calkidd Well-Known Member

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    He's is extremely helpful and if need be he'll send you his phone number and talk you through more complicated matters that cannot be explained through PM's
     
  4. joe kuhn

    joe kuhn Furry Lives Matter TS Supporters

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    Hi Larry. Which setting works best for you for breaking targets?
     
  5. GrandpasArms

    GrandpasArms Active Member

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    Joe;

    I find 3/8 inch comb rise is about right - with a standard rib on my BT99 (old BT, flat shooter). This adjustment keeps my POI about 8 inches high at 35 yards. It seems to work for me as long as it's daylight. Once darkness hits, all bets are off. I'm working on that problem, but no answer yet.

    I see that most gun-talk mentions percentage high or low (80/20, 70/30, etc.). However, I think it's more accurate for me to measure my pattern center and know that it is X inches at Y yards. As I mentioned in the beginning of this thread, I tested Rolin Oswald's reported calculations at St. Charles at 35 yards ( in the 8 inch ballpark).

    Just for grins I backed up to that 45 yard mark and shot a pattern with the same settings. It was more difficult to visualize the center of the pattern, but I conclude it almost 12 inches. Oswald's formula calculated to a little over 13.

    This is different if I'm using a shorter gun. It's 44 inches from my eye to the muzzle on the 34 inch BT99. The calculated POI is greater with a shorter distance. That's why it's important to not crawl the stock - it shortens the distance from eye to muzzle.

    The final adjustments was for comfort. I moved the comb out, away from my face and lowered the butt plate (and tipped the foot out).

    Larry
     
  6. Rollin Oswald

    Rollin Oswald Active Member

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    Larry,

    I cannot take credit for the equation (or the sutomatic POI calculator that does the math for you). The drawing and formula was devised by Doug Pilcher (Shotgunworld's "Rastoff") and the automatic POI calculator was created by Jesper Greth who lives and shoots in Finland.

    If anyone wants the drawing, formula and calculator, email me. Put "POI calculator" in the subject line and I will reply with them attached. The POI calculator uses Microsoft Excel, which is part of MS Office. If you don't have it on your computer, it is available as freeware if you Google "excel" and download it.

    Rollin
     
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