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Old January 1, 2019, 10:49 PM   #27
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Join Date: November 26, 2016
Posts: 790
Originally Posted by Unclenick View Post

There's a story to it. I had just finished tightening and fitting up the gun for bull's-eye pistol matches and was shooting lead through it off the bench. It was grouping about an inch at 25 yards range with the cast bullets from a bag with iron sights. I was very satisfied with that. Especially since I was having trouble with the bag I brought being a little short for the job, making me put it up on a stack of targets that kept slipping a little.

On the next firing point was a friend with a Hoppe's pistol rest (no longer made) and an Aimpoint sight on one of those left grip panel replacement mounts. He was throwing nearly 3" groups using the load I wrote down. He had actually loaded them on my equipment a week before the range session. My powder and primers; his cases and bullets. He had just put a Colt National Match barrel in his gun, but just as a drop-in that he hadn't fitted to the gun in any way. I explained he needed to do that. Nonetheless, he was questioning the sight and wanted me to try it. So I swapped the grip panel mount and sight onto my gun and shot the five for the group without zeroing the sight. That's why the group is high on the target.

Since I didn't have a spotting scope with me that day, I couldn't see what had happened from the bench. So I swapped the sight back onto the owner's gun while we waited for a cease-fire to go see what the damages were. Not too bad. Obviously, it proved the sight and the load were fine. He decided he needed to fit up his gun after that.

I was tickled with the group but didn't like the weight of the Aimpoint with the cast metal grip panel mount for offhand shooting (as match rules required). So I never got one of those rigs nor had occasion to repeat the feat. I just know what we loaded for him.

Statistically, a five-shot group isn't impressive. If I assume the worst and that it was just lucky on the small side, based on 95% confidence, a five-shot group with an average size of 1 unit of measure (an inch, a centimeter, a foot; whatever) will randomly vary from 0.652 to 1.53 times the average. So I can say with 95% confidence that the average group would be no bigger than 0.567" if that one was on the small side. On the other hand, if it was on the largest side, the average group would be just 0.25". Even though human intuition says it is more likely the former than the latter, the odds are actually equally high in either direction. The odds are 2:1 the average 5-shot group size over many more samples would turn out to be between 0.306" and 0.468", and are only 1:40 that the group was an outlier (outside the range for 95% of all 5-shot groups I might fire with the same ammo and conditions) on the small side.
Thanks for the reply. You could have saved yourself some time and just said that you fired only one 5-shot group. That would have answered my question.
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