Question about mean radius

Hello all -

I'm not the best shooter in the world. I was able to shoot an 2 MOA group with IMI Razor Core 77gr. There were definitely some user-induced fliers. The mean radius of the group, however, was .66". My question about mean radius is as follows: if I'm trying to determine the accuracy of a round, Say the IMI razor core, is it better to use the actual MOA size of the group, or multiply the mean radius by 2? Theoretically, that would give you the diameter of a group you could expect.

Any input on this guys?
Thanks

2 different measurments. Pure performance, mean radius. Capabilities to make decisions with, I'd use ES as that tells you where every round will go.

I'm not an expert, but that's what id do.

Mean Radius has been beat to death, because the military uses it. I use Extreme Spread when measuring groups. If 9 rounds go inside a 1" group at 100 yards and the 10th round on target opens the shot group to 1-1/2", in my opinion I have a rifle that will shoot 1-1/2".

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Originally Posted by T2C

Mean Radius has been beat to death, because the military uses it. I use Extreme Spread when measuring groups. If 9 rounds go inside a 1" group at 100 yards and the 10th round on target opens the shot group to 1-1/2", in my opinion I have a rifle that will shoot 1-1/2".

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The military uses it for good reason, because it is statistically superior.

The issue with your extreme spread example, is that if 9 rounds produce a 1'' group, and the 10th produces 1.5'', then shooting 20 rounds will probably produce 1.75'', and shooting 30 rounds might produce 2''. It's a moving target, unpredictable and unreliable. More shots fired equals bigger ES.
With Mean Radius, the more shots you take, the more the Mean Radius observed value settles into it's true value. It gets more and more reliable, AKA the confidence interval improves.


I'm a Mean Radius fanboy. ES has it's limited place as does looking at stringing, patterns, hot POI vs cold, ect, but most of that can be assessed with the eyeball. But when measuring and math are applied to try and determine the mechanical precision of a rifle, I'm using MR (MR, ATC, AMR all the same thing).

To answer the OP, you can't multiply MR to get ES or vice versa. They are different. Some try to do some mental gymnastics but I think they are chasing their tail. How many rounds did you shoot in that group? If less than 10 I'd say don't bother with measuring anything. 10 is good, 20 is better yet. MR of 0.66 is not good. I'd work on shooting more groups, trying to stop the fliers from happening so you can be confident of your result. Dry fire in between strings. Take notes and keep records.

It was a 10 round group. I need to work on breathing and more consistent trigger pulls I think

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Originally Posted by XD40Colorado

It was a 10 round group. I need to work on breathing and more consistent trigger pulls I think

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Get a good springer air rifle (but do NOT go for a high velocity one), use aperture sights, shoot rested and offhand and you'll get a TON of "trigger time" in no time. Focus on front sight and where it is WHEN the trigger breaks. Learn to call your shots.

And lastly - practice with a sense of purpose. If you're off ... put it away, you don't want to learn bad habits, as they are a bitch to UNlearn ...

I wrote this a while ago, seems pertinent:

https://www.m4carbine.net/showthread...-Accuracy-quot

I understand the concept of Mean Radius and it's usefulness for determining precision of a weapon system with different types of ammunition. Unless I am shooting a rifle or carbine off a rest, taking the time to determine Mean Radius is not as expedient as Extreme Spread while on the rifle range.

If a concentric group is shot, doubling the Mean Radius value would give us a rough Extreme Spread value. If 8 of 10 shots are touching and 2 shots are a good distance from the 8 shot group, doubling Mean Radius would give a false reading in my opinion.

Mean Radius is an excellent tool for determining repeatability of a weapon system. If you work in the firearm industry or are testing a weapon system for purchase by an agency or training facility it's the way I would calculate precision. Extreme Spread is more expedient.

Personally, I work on shooting consistency and group concentricity with a chosen weapon system and cartridge before taking the time to calculate Mean Radius.