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20 consecutive 5 shot groups at 50y to test dispersion theory

thomasair

Member
Manufacturer
Nov 6, 2016
2,253
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Colorado, United States
Ballistician Bryan Litz posted an interesting dialogue on dispersion on Facebook.

https://www.facebook.com/BryanLitzBallistics/

In a nutshell…he proposes that if you shoot 20 5 shot groups, your largest group will be approximately 4x your smallest group and your average will be about 2.5x your smallest.

That is pretty close to what I’m seeing in this 20 group sampling at 50y. My smallest to largest is about 3.5x. This could mean that over a greater sample size I might get a slightly smaller average “small” group or a larger average “big” group.

Pretty interesting….If you read the whole dialogue.

Mike 

6F114255-6ED4-4A4B-B481-8E51D4DF4462.1653505745.jpeg



 
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Terrible shooting.....is what I'm gonna think everytime I shoot at 50yds now. First off wow 20 5 shot groups at 50yds avg barely over 1/2 MOA. Which gun is it? I mean obviously Thomas but is this the HP?

Interesting theory for sure. Looks to be very logical. What I notice on yours is your largest is almost .083" larger than your second largest. If it wasn't for that group it'd be 2.86x your smallest, closer to what the AVG would be based on his theory. However I wouldn't say the Thomas and the man behind it are AVG at all when it comes to shooting.
 
Ballistician Bryan Litz posted an interesting dialogue on dispersion on Facebook.

https://www.facebook.com/BryanLitzBallistics/

In a nutshell…he proposes that if you shoot 20 5 shot groups, your largest group will be approximately 4x your smallest group and your average will be about 2.5x your smallest.

That is pretty close to what I’m seeing in this 20 group sampling at 50y. My smallest to largest is about 3.5x. This could mean that over a greater sample size I might get a slightly smaller average “small” group or a larger average “big” group.

Pretty interesting….If you read the whole dialogue.

Mike 

6F114255-6ED4-4A4B-B481-8E51D4DF4462.1653505745.jpeg





To bad it's on Facebook. I refuse to ever go back on FB ever again.












 
I guess what the takeaway should be is that the big group should be expected based on the small one. That’s the woulda, coulda, shoulda group that actually belongs there. I could not have done anything to prevent it. If I was shooting a BR card I might have gotten lucky and the very highest shot of that group could have occurred when I was on a sighter…but it was still destined to happen in a 100 shot sample. I don’t believe that shot was due to any wind I was experiencing.

Based on the typical dispersion….it would be almost impossible to make any sound decision about a particular change with only a few groups. The closer you get to the max….the more tedious it becomes to be able to even tell if you’ve done anything to improve the gun.

This is a Thomas Slug gun. 

Mike


 
Yeah, that is how the math works. Statistics. Good to see someone write it down that you can trust. Mind you that is with GOOD AMMO which has not been sorted. You sort it and the groups WILL improve. The thing that will really "bake your noodle" is the same ratio will hold after you sort it. Don't take my word for it. Take Bryan's.

Damn fine shooting.

We discussed this in my Oldspooks incarnation five years ago:

https://www.airgunnation.com/topic/what-is-standard-deviation/#post-159210

https://www.airgunnation.com/topic/what-is-standard-deviation/page/2/#post-159409
 
Very interesting, whenever I see the groups that some sellers show, they must be their best groups (it would not make sense to show a bad group or a regular group) taking into account the dialogue, the best group is only 1 of 20 and for that good group it has to there may be a bad one of 4.5X, in Mike's case 3.5X.

In my case I received a very fine new rifle that comes with a card with a group of 5 very good shots, no matter how hard I try I cannot repeat that group. It's just that now I understand that the card that comes to me is not the average, but the best group, which is real, yes, but it's not the average.

Jorge
 
To bad it's on Facebook. I refuse to ever go back on FB ever again.


You can find his books and such at appliedballisticsllc.com or thescienceofaccuracy.com. He has some great books and knows what he is talking about. Most of the info is on centerfire and a little rimfire, but he is interested in getting into slugs and pellets in the near futurel

--Jim
 
Jorge….I would expect that pretty much every 5 shot group that gets posted on a forum is done because it’s out of the ordinary. It’s the 1/20 or maybe even the 1/100.

Here is the same gun in similar conditions on a N50 card. Bull 22 is a big flier of unknown origin. After I finished up I went back and shot it again. Don’t think it was any wind condition miss. It’s fairly common to have one shot that is unexplainable per card. Sometimes you get lucky and it ends up on a sighter so you can get a clean card. Barrels seem to run in cycles. Too many great shots in a row gives me a bad feeling that something is coming that will even things out. If I have a near miss that does something odd, like go against a pretty solid condition….I get off the card and shoot on a sighter til the barrel settles back down. Sometimes you get no warning.

Mike

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