The velocity averaged 2622 fps, SD 14 (.5%). The BC was .493, SD .007 (1.4%). The group was 1.152", primarily vertical. Maybe the 12 o’clock damage was inducing some up and down movement.
That wasn’t so bad, maybe I can do better. I took a pin punch and a hammer and punched a burr into the bore on one of the lands. The first shot broke off the burr and launched it out of the barrel. A small copper colored cloud was briefly visible, possibly from the jacket impacting the burr. The group was .676", the velocity averaged 2633 fps, SD 15 (.6%), and the BC was .490, SD .007 (1.4%). (See Photo 2)
Photo 2 – shows a burr punched onto the land to the left of the notch shown in Photo One. Sorry it’s blurry … must have been the earthquake.
OK, no more Mister Nice Guy. Time for the carbide burr. I made a half moon cut out at the crown. It resulted in a .751" group, a velocity of 2622 fps, SD 7 (.3%), and a BC of .485, SD .008 (1.6%). I hate to say it, but it’s almost like the crown doesn’t matter. Nah, couldn’t be!
Mr. Beaufort thought I was being too gentle, so he tried his hand at a little precision gun plumbin’. He wallered that carbide burr around the crown and down inside the barrel to a depth of maybe half an inch. I’ve never broken a carbide burr in a barrel, but I’m here to say it can be done. He also breaks the heads off scope base screws. And after he participated in a USMC shotgun endurance test, the Marines, not generally considered pansies, told him that he was hard on their guns. Applying that same enthusiasm, he made an absolute mess of the last half inch of the barrel. We concluded that any hopes of accuracy were now gone. (See Photo 3)
Photo 3 – What happens when you go wild with a carbide burr. The criminal responsible for this indignity will never be allowed near a Bartlein or Krieger again.
They were… at least for the next two shots, which made a group of 1.740". This group is heading South. Wait – keep shooting. The next five rounds made a group of .697". The velocity for those seven rounds averaged 2615 fps, SD 8 (.3%), and the BC was .492, SD .007 (1.4%).
Somebody want to explain these results? How can a barrel with a crown that has been absolutely destroyed shoot under ¾ MOA? Beats me. I saw it and I still don’t believe it. Well I do believe it because I saw it, but I can’t explain it. And since I can’t explain it I am going to continue to insist on having as perfect a crown as is possible. But if I ever see a guy shorten a barrel with a hacksaw, knock off the sharp edges with a file and crown it with an RCBS case mouth chamfering tool, I don’t think I’ll tell him that it won’t shoot. I’ll just wait and see.
By the way, I ran an unpaired t test to compare the BC means (averages) and found that the difference between the ‘Fresh crown’ BC and the ‘Damage 4’ BC is considered to be not statistically significant at 95% confidence.
… Weeks pass and the earth turns. This still doesn’t make sense. Since this doesn’t make sense I must be coming up with the wrong answers or else I haven’t asked the right questions. Here’s a Q and A that I’ve heard and believe – What is the last part of the barrel to touch the bullet before it takes flight? Answer – the crown. So with a Q and A like that, the obvious conclusion is the belief that the crown must be perfect to have perfect bullet flight. Maybe that’s a good question but not the best question. Or maybe that’s a good question for rimfires but not so important with jacketed bullets. So what other questions should I ask? Maybe there are other factors that I should have considered.