TUNING

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  • Last Post 21 August 2022
joeb33050 posted this 17 August 2022

Mr. Shooter has a rifle that averages .200” for 5-shot 100-yard groups.

 

Mr. Shooter wishes to detect any change in accuracy and tune the equipment to “fix” the accuracy. He fires one 5-shot 100-yard group.

 

The table shows the possible outcomes and the probabilities of those outcomes for rifle accuracy of .200” and .220”5-shot 100-yard groups.

 

For instance, groups > .230” will be shot 27% of the time from a .200” rifle, and 41% of the time from a .220” rifle.

 

 How does Mr. Shooter decide when to tune, and when tuning has fixed the accuracy?

 

 

 

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Pentz posted this 21 August 2022

If I understood any of this I'd be bewildered.....dizzy

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John Alexander posted this 21 August 2022

I think I agree with Aaron.

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45 2.1 says: "While in my late 20's and early thirties, I shot 5 shot groups at 100 yards off the bench for many years. The powder was Unique in various scope sighted rifles. Groups varied some, but seldom more than 1/4" variance. unless the wind gusted. "

=======

If this is saying what I think it says i.e. 5-shot groups only varied a 1/4" inch from one group to the next, may I respectfully suggest that your memory of those by-gone years may be a bit cloudy. Strings of 5-shot groups are shot in group matches all the time so we have massive amounts of data on how strings  of 5-shot groups vary from one group to the next. The AVERAGE ratio of largest to smallest group in strings of five 5-shot groups will be near 2.  This holds true whether the group size is 0.2" or  5". It is a very rare event when the groups in a string of groups are nearly alike, and not an event that can be repeated the next try. If you don't believe this look at any match report of a group match, or better yet shoot a string of five 5-shot groups and see for yourself.

As for the order of shots determining the location of individual shots in the group time after time, I would encourage interested shooters to start with a cold barrel and try to duplicate this wondrous feat before betting any serious money on it.

John

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Aaron posted this 20 August 2022

With rifle in hand, I confidently go forth into the darkness.

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45 2.1 posted this 20 August 2022

Any Thoughts......................

Yes, here are some.

While in my late 20's and early thirties, I shot 5 shot groups at 100 yards off the bench for many years. The powder was Unique in various scope sighted rifles. Groups varied some, but seldom more than 1/4" variance. unless the wind gusted. The groups basically shot in the same bullet placement for each numbered shot in the group most every time. I'll describe in terms of polar coordinates if you understand that terminology. The first shot was at 40 degrees up from the point of aim, the second shot was at 200 degrees down from the point of aim, the third shot was at zero degrees up from the point of aim below the first shot. numbers 4 & 5 were between the 3rd and 2 second shots. In 80% of all tracked recorded groups this showed to be what happened in all groups. This is basically barrel heating showing in years of shooting. The group size was the first two shots. You notice that I didn't relate group size. This was with a 1903A3 two groove barrel with the RCBS 308-165-Sil bullet sized 0.311" and loaded with Unique to about 1,500 fps. In all that time I never experienced what you and John have talked about. Maybe you could have some thoughts about that. 

 

Interesting observations!  That supports the common practice of timing of shots to control the temperature (hence resonate point repeatability) of the rifle.

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They were shot from a cold barrel (in all temperature situations over the year) at about 30 seconds per shot. No foulers. When you got to shots 6, 7 and beyond the barrel heating went out of the group up and to the right in all cases. The really interesting thing is you could average each shots placement (for that numbered shot) and shoot a cheaters group holding off for that shots average displacement and shoot groups totally stupidfingly abnormal and preposteruring small totally out of character for the gun. I tried that for a couple of months one summer in three rifles and got some preposterous groups. A few powders have Unique's ability to do this. This happens to be a charge where the barrel vibrations are at a node and very well balanced.

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TRKakaCatWhisperer posted this 20 August 2022

Any Thoughts......................

Yes, here are some.

While in my late 20's and early thirties, I shot 5 shot groups at 100 yards off the bench for many years. The powder was Unique in various scope sighted rifles. Groups varied some, but seldom more than 1/4" variance. unless the wind gusted. The groups basically shot in the same bullet placement for each numbered shot in the group most every time. I'll describe in terms of polar coordinates if you understand that terminology. The first shot was at 40 degrees up from the point of aim, the second shot was at 200 degrees down from the point of aim, the third shot was at zero degrees up from the point of aim below the first shot. numbers 4 & 5 were between the 3rd and 2 second shots. In 80% of all tracked recorded groups this showed to be what happened in all groups. This is basically barrel heating showing in years of shooting. The group size was the first two shots. You notice that I didn't relate group size. This was with a 1903A3 two groove barrel with the RCBS 308-165-Sil bullet sized 0.311" and loaded with Unique to about 1,500 fps. In all that time I never experienced what you and John have talked about. Maybe you could have some thoughts about that. 

 

Interesting observations!  That supports the common practice of timing of shots to control the temperature (hence resonate point repeatability) of the rifle.

 

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John Alexander posted this 18 August 2022

It may be helpful to readers to know that speaking of polar coordinates is just a pretentious substitute for the more common way shooters describe hits on a target as hits on the face of a clock.  90 degrees in polar coordinates = 3:00 O'clock, 180 degrees = 6 O'clock,  etc.

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45 2.1 posted this 18 August 2022

Type the first two words in a internet search query and see what you find.

 Here is a good example. This is engineering at the beginning stages of course.

https://mathworld.wolfram.com/PolarCoordinates.html

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joeb33050 posted this 18 August 2022

Polar coordinates? What's that buzzing I hear? If you think that bullets form the same pattern for each/every group shot; you're alone. Bullets don't go through the same hole, ergo groups. Because hole location varies, group size varies, in a predictable fashion. And single groups contain little information about average group size. This is explained above. Polar coordinates? 

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45 2.1 posted this 18 August 2022

Any Thoughts......................

Yes, here are some.

While in my late 20's and early thirties, I shot 5 shot groups at 100 yards off the bench for many years. The powder was Unique in various scope sighted rifles. Groups varied some, but seldom more than 1/4" variance. unless the wind gusted. The groups basically shot in the same bullet placement for each numbered shot in the group most every time. I'll describe in terms of polar coordinates if you understand that terminology. The first shot was at 40 degrees up from the point of aim, the second shot was at 200 degrees down from the point of aim, the third shot was at zero degrees up from the point of aim below the first shot. numbers 4 & 5 were between the 3rd and 2 second shots. In 80% of all tracked recorded groups this showed to be what happened in all groups. This is basically barrel heating showing in years of shooting. The group size was the first two shots. You notice that I didn't relate group size. This was with a 1903A3 two groove barrel with the RCBS 308-165-Sil bullet sized 0.311" and loaded with Unique to about 1,500 fps. In all that time I never experienced what you and John have talked about. Maybe you could have some thoughts about that. 

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joeb33050 posted this 18 August 2022

Re-arranging the table, we can more clearly see Mr. Shooter’s dilemma.

If, for example, he selects .240”-.250” or larger as his “trigger” group size, the group size at which tuning is done; then he faces the probability of 4% that the group comes from a .200” rifle, and 6% that the group comes from a .220” rifle.

If his single test group is .240”-.250” and he tunes something; then he must fire a group to test the tuning. If the tuning test group is .190”-.210”, the probabilities are 8% of a .200” rifle, and 7% of a .220” rifle.

 

Mr. Shooter faces an array of probabilities before firing his first test group. The rifle may have remained a .200” rifle, in which case the first test group of .240”-.250” has a probability of 4%; or a first test group of > .260” with a probability of 13%.

Or the rifle might have turned into a .210” or .240” or… rifle, with other sets of probabilities.

And the tuning test group can be from a “fixed” and now .200” rifle, or from a “fixed” and now .220” rifle.

 

Mr. Shooter faces the problems of selecting the first group “trigger” group size, and the “tuning worked” group size.

 

Any thoughts?       

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