Doughnut for Joe

In the thread “An accuracy test for Joe B” started by RicinYakima the discussion wandered to the question of ”€œ “If defects make a bullet fly away from the group center why don't we see doughnut shaped groups.”  Joe posted groups shot with bullets he had filed a notch in and sure enough instead of a donut more shots were near the center, more like a donut hole.  Joe challenged anybody to shoot a donut and I said that I would try and donut or not would post the results ”€œ then my regular life got in the way and it took a while. Then after I had shot the donut my computer had a fit and wouldn't let me post pictures.  By now readers have probably forgotten the original discussion but here are the results.   I followed Joe's suggestion and used a 22 rimfire. An old Remington M-37 with the barrel chopped off short. I made a simple gadget to hold the cartridge in my drill press and made the defects with a center drill.  The point on the drill used looked like the 135 degree type so the hole was big and shallow thus as far from the long axis as possible so as to do the most damage. Joe had tried defects that removed .1 and .3 grains from the bullet.  I had suggested that the reason he hadn't seen a donut was the defect was too small compared to the precision of the loads. My first round of defects were .3 grain.  In spite of indexing, I too got a hole instead of a donut with more shots tending toward the center of the group than the outside -- just as Joe had.  This is not a small defect.  On a 200 grain bullet it would be a big ugly 1.5 grain hole on the outside of the bullet. Even so the 7 shots, before I gave up, made a group that was a bit over 2 moa. Not such bad accuracy for bullets with a big defect.   I wound up using a defect that removed 1.1 grains from each bullet or close to 3% of the bullet weight. With that size defect I shot a pretty reasonable donut.  The first three shots were with unmutilated bullets and made a .52 moa three shot group near the aiming point.  I drilled the defect into eight bullets and made crude indicting marks on the rim.  The first two were fired with the index marks at 12.  And the length of the barrel and twist combined to throw the two shots towards 12.  The next two were indexed at three and hit at 3 and 40. The two indexed at 6 made one hole at 7 and the two indexed at 9 went towards 100 with one way out. For the very crude indexing I think this confirms that a point defect will cause a deflection in a predicable direction just as Mann, Vaughn and others claim.  I haven't tried to quantitative check the predicted magnitude of the deflection with Vaughn's formula yet. Note that even with a huge point defect removing 3% of the bullets weight the average deflection was only a bit over 2 moa.  Please excuse two pictures of the target I can't get rid of one. John