MEAN RADIUS

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joeb33050 posted this 18 November 2018

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Scearcy posted this 18 November 2018

Joe

Interesting stuff. A few years ago I did a lot of load testing with a 300 Blackout. I, along with a couple of other guys here on the forum, used MR calculations for most of that testing. It is interesting that over time we reached the conclusion that a worthwhile match load should produce MR> .4" (10  shot groups). We had more confidence in MR stats than we did in GS numbers. Your table supports them being equally reliable measures if enough groups are employed. I wonder if both averages converge on the true value at the same rate. ie after three 10 shot groups will both measures be equally reliable predictors of our ultimate group size? What do you think?

Jim

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joeb33050 posted this 18 November 2018

An  MR of .4, for 10-shot groups, = GS of ~1.1" for 5-shot groups.

Shots / group has ~ NO effect on test accuracy.

Samples avg of GS or MR or shoe size have sample s = SIGMA / sqrt n, so both approach TRUE AVG at the same percentage rate.

Let stdev of MR = 1, and GS = 3.453.

Samples of 4:  stdev MR = 1/sqrt 4 = 1/2; stdev GS = 3.453/ 2 = 1.726

~95% of the time TRUE AVG is, MR, test avg +/- 2s = +/- 1;;GS, test avg +/-2s =+ /- 3.453;;both +/- 100%

Samples of 100:  stdev MR = 1/sqrt 100 = 1/10 = .1; stdev GS = 3.453/ 10 = .3453.

~95% of the time TRUE AVG is, MR, test avg +/- 2s = +/-.1;;GS, test avg +/- 2s = +/- .3453;;both +/- 10%

I think.

 

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Scearcy posted this 19 November 2018

One thing I like about mean radius is that you can add the groups together. As long as you do not change your point of aim by adjusting your scope it is very interesting to watch the calculated center of the group converge with the POA. Usually by the time you have twenty shots recorded, the POA and the COG are within a tenth of an inch of each other.

I like to do a scatter chart of the bullet strikes. After twenty shots your fliers "melt" into the group and whaat remains is a very accurate picture of what the load will really do.

Jim

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John Alexander posted this 19 November 2018

Interesting post. The most interesting part for me was the statement that "After twenty shots your fliers "melt" into the group.)

In other words  the "worst shot" in a five or ten shot group (the bullet holes that 90% of CB shooters insist on calling "fliers") aren't fliers at all in the sense that that there was something wrong with the individual shot but just part of how well the rifle/ammo/shooter combination will actually shoot. 

Except for the rare perfectly round group all groups have a worst shot.  If it doubles the size of the group it may make sense to consider it something wrong with that individual shot. If it has somewhat less effect on the extreme spread you are probably off on a wild goose chase trying to find what was wrong with that bullet and buying a bigger magnifying glass to no avail.

Husker (Larry Landercasper) tried to show us the truth about fliers a few years ago on this forum by shooting five 5 shot groups, all five with one "bad" shot and the composite 25 shot group where all the fliers disappeared.  The big group showed the individual groups in different colors so you could see the shots that used to be fliers most of them well within the 25 shot group. That great visual demonstration of something few CB shooter understand apparently "didn't take" and most of us are still wasting time curing fliers.

I think the importance of this is that not understanding that the worst shot in your groups is just natural variation leads to such things as sorting bullets to .1 grain and discarding bullets with slightly rounded edges and a multitude of other anal things that will not improve accuracy a whit (technical term meaning I.349687 angstroms -- more or less). When they should be looking elsewhere.

Pity.

John  

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joeb33050 posted this 19 November 2018

Interesting post. The most interesting part for me was the statement that "After twenty shots your fliers "melt" into the group.)

In other words  the "worst shot" in a five or ten shot group (the bullet holes that 90% of CB shooters insist on calling "fliers") aren't fliers at all in the sense that that there was something wrong with the individual shot but just part of how well the rifle/ammo/shooter combination will actually shoot. 

Except for the rare perfectly round group all groups have a worst shot.  If it doubles the size of the group it may make sense to consider it something wrong with that individual shot. If it has somewhat less effect on the extreme spread you are probably off on a wild goose chase trying to find what was wrong with that bullet and buying a bigger magnifying glass to no avail.

Husker (Larry Landercasper) tried to show us the truth about fliers a few years ago on this forum by shooting five 5 shot groups, all five with one "bad" shot and the composite 25 shot group where all the fliers disappeared.  The big group showed the individual groups in different colors so you could see the shots that used to be fliers most of them well within the 25 shot group. That great visual demonstration of something few CB shooter understand apparently "didn't take" and most of us are still wasting time curing fliers.

I think the importance of this is that not understanding that the worst shot in your groups is just natural variation leads to such things as sorting bullets to .1 grain and discarding bullets with slightly rounded edges and a multitude of other anal things that will not improve accuracy a whit (technical term meaning I.349687 angstroms -- more or less). When they should be looking elsewhere.

Pity.

John  

There's 5-shot-group world, and 10-shot group-world, and zillion-shot-group world. Zillion-shot groups have NO flyers, and are a zillion inches across, with mean radius of a zillion yards.

You guys are playing "what if", what if we shoot more shots, will the flyer go away?  Shoot enough shots and ANY flier gets surrounded. But didn't we know that? Flyers are out there, I've captured many. 

 Hiding flyers with more shots? Why not masking tape?

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Larry Gibson posted this 19 November 2018

There is another "world" besides the "There's 5-shot-group world, and 10-shot group-world, and zillion-shot-group world. Zillion-shot groups have NO flyers, and are a zillion inches across, with mean radius of a zillion yards."  That world is where/when we shoot for score. 

Thus I'm inclined (after many years shooting for score in various disciplines) to agree with scearcy's statement of;

"After twenty shots your fliers "melt" into the group and what remains is a very accurate picture of what the load will really do" based on shooting several groups w/o sight adjustment.  That gives us a "cone of fire" and more readily indicates the loads performance than does the measurement by any method of 5 or 10 shot group measurements alone. 

I have watched many a shooter (including myself, been there done that) lose points when shooting for score by "chasing the spotter" (or bullet hole if it can be seen) making sight changes based on a previous "group size".

LMG 

 

Concealment is not cover.........

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Paul Pollard posted this 19 November 2018

John,

it seems hard to ignore “fliers” in our group shooting. Look how small those groups could be!

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John Alexander posted this 20 November 2018

Joe wrote:

""There's 5-shot-group world, and 10-shot group-world, and zillion-shot-group world. Zillion-shot groups have NO flyers, and are a zillion inches across, with mean radius of a zillion yards.

You guys are playing "what if", what if we shoot more shots, will the flyer go away?  Shoot enough shots and ANY flier gets surrounded. But didn't we know that? Flyers are out there, I've captured many. 

 Hiding flyers with more shots? Why not masking tape?"

===========

I started to give a wiseass answer that the mean radius of a zillion shot group would be only a zillion feet instead of yards. Then realized the MR wouldn't increase to a zillion anything. It would stay more or less the same after twenty or thirty shots right up to a zillion. Or maybe I don't understand it?

I didn't know I mean to be playing "what if".  What I was trying to say was, if shooters keep on considering the the worst shot in a five shot group that adds 25% to the size of the four shot group and the worst shot in a 10 shot group that adds 15% to the size of the best nine and and consider them somehow defective shots they will look for solutions in the wrong places because if you stack up five of the five 5-shot groups into a 25 shot group the horrible fliers will all disappear into what Larry calls a cone of fire.  Even worse, some of them may be very close to the center of the 25 shot group. How can you consider a shot close to the center of a large group a flier (defective shot) with a straight face?

Nobody is saying that there aren't real fliers (caused by the individual shot because defects in the load or the shooting. Of course there are.  But they are seldom the slightly worst shot like the ones in the groups Paul posted (except one maybe).

I hope this discussion doesn't degrade into an argument about whether 5 or 10 shots are "best" because that long lasting, but silly argument, should embarrass us all.

John

 

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RicinYakima posted this 20 November 2018

They are "outliers" not "flyers". joeb has convinced me that unless it is a shooter error, it is most likely just a datum point away from the center of the group. Larry has convinced me that the best we can do is concentrate a higher percentage of our "cone of fire" (remember that from my M60 machine gun days) closer to the middle of the group.

I am hoping that there is some technique that will allow closer grouping with just cast metal without having to rely on a copper jacket for bullet material.

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Ed Harris posted this 23 November 2018

FWIW the military switched to radial standard deviation some years ago.

That should give Joe a whole new universe to enlighten us upon.

With a patched round ball muzzleloading rifle how many shots does it take to determine if the rifle is a "keeper?"

For me if I can hit a 12" steel gong with iron sights with my first shot, standing on my hind legs at 100 yards, that is "minute of deer."

I can then postulate whether I should spit patch between shots or chance reloading a fouled bore.

I have found from practical observation that pillow ticking patches lubricated with spit only are good for three shots fired within 3 hours on a cold, snowy day.  That is fire first shot from a clean barrel, reload the gun, set it in the rack and do something else for an hour, repeat, do it again, and empty the gun for the last time before it gets dark.  Three shots, three hits, simplicity itself.

No measuring needed.

Have found that a loaded gun with spit patch may throw a flier if left loaded until the next day, because it dries out.

So shoot and clean before supper, reload in the morning, or introduce another variable.  Is lard oil better than spit?

West Virginia hillbillys say so, if you plan to leave your "home rifle" loaded for days on end, propped by the kitchen door in anticipation of a fat doe wandering into your garden.  But the same group also argues that spit generated from chewing Red Man tobacco is better than that produced by Mail Pouch because it has less sugar. 

I, myself, prefer black coffee spit because "chaw" is a filthy habit and I wouldn't want the milk to go sour in the bore...  Brit black powder shooters state that the spit produced from drinking hot, (never iced!) unsweetened black tea is best.  Since our neighborhood Brit expat wins our cash pot fairly regularly using this method I am not one to argue.

Also one must not use treated water from a municipal supply to make tea.  Such is an abomination.  Here we use Berkeley Spring water  http://berkeleysprings.com/berkeley-springs-spas/water-facts-and-fiction/  The Virginia Legislature included the statement that the water shall remain free for the public in its law establishing the town of Bath at the springs in December 1776.

73 de KE4SKY In Home Mix We Trust From the Home of Ed's Red in "Almost Heaven" West Virginia

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beagle6 posted this 24 November 2018

When I served in the Field Artillery, everything was based on probability, range probable error and deflection probable error. In spite of 10's of thousands of test firings,it was verified that 7 rounds out of 1000 were completely unpredictable. Ed, are you sure your neighbors don't lube their patches with moonshine?

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Ken Campbell Iowa posted this 24 November 2018

.... in west virginia, there is already plenty of moonshine in their spit .... even the hound dogs slur their barks when they tree ....   snakes there think they are slithering in straight lines to fool the cops ... after using the outhouse, west virginians don't use anti-bacteri Wipes, they just sweat ....

my kind of country ...

ken

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