Mean Radius for Bullet Testing ?

[DagOtto]

Hi,

I’m curious as to people’s input on using mean radius vs. max spread for bullet selection.

I have a new rifle in 6.5 CM, I’ve been shooting 10 shot groups of various factory loaded bullets to try to determine which bullet to go with. I don’t reload.

I’m 7 groups in so far. My 10 shot groups have varied from .48 -.70 inches and max spreads have varied from 1.72-2.16 Inches. I’m shooting off of sand bags on a bench at 100 yards. I count all shots. (No flyers) I’m using the group analysis tool on the Hornsay 4FOF app to document and measure.

I’ve heard lots of people indicate that for determining maximum ethical shooting distances one should use maximum spread which makes sense to me.

But, my question is in relationship to picking the most accurate bullet. Shouldn’t I use mean radius for that?

My reasoning is that my own shooting form (or lack there of,) is likely causing the two worst bullet placements in a group of 10. It seems unfair to blame the bullet for what is very likely my own shooting errors.

Because of this it seems more realistic that the most accurate bullet will be indicated by Mean Radius.

Thoughts ?
DO

 

[DagOtto]

A follow-up thought:

Would a more accurate way to determine most accurate bullet be to remove the two worst impacts in each group of 10 and then recalculate the mean radius from this “high-graded” group? Again, the goal would be to see a more true analysis of the performance of the bullet by eliminating shooter error.

 

[Formidilosus]

Hi,

I’m curious as to people’s input on using mean radius vs. max spread for bullet selection.

I have a new rifle in 6.5 CM, I’ve been shooting 10 shot groups of various factory loaded bullets to try to determine which bullet to go with. I don’t reload.

I’m 7 groups in so far. My 10 shot groups have varied from .48 -.70 inches and max spreads have varied from 1.72-2.16 Inches. I’m shooting off of sand bags on a bench at 100 yards. I count all shots. (No flyers) I’m using the group analysis tool on the Hornsay 4FOF app to document and measure.

I’ve heard lots of people indicate that for determining maximum ethical shooting distances one should use maximum spread which makes sense to me.

But, my question is in relationship to picking the most accurate bullet. Shouldn’t I use mean radius for that?

No. How do you know whether you have a “good” bullet in the chamber, versus a “bad” bullet in the chamber?


And why- is it always the shot the people don’t like that are “them”, being that guns shoot to a cone.

My reasoning is that my own shooting form (or lack there of,) is likely causing the two worst bullet placements in a group of 10. It seems unfair to blame the bullet for what is very likely my own shooting errors.

Not unless you are having a seizure behind the rifle. If you can shoot 2 shots without flushing behind the rifle, you can shoot 10. But again, it’s always the shots you don’t like that are “caused by me”.

Because of this it seems more realistic that the most accurate bullet will be indicated by Mean Radius.

Thoughts ?
DO

Your belief starts with a massive incorrect assumption (that is the shots you don’t like were “you”), and because of that incorrect assumption you are how convincing yourself of an incorrect conclusion.

 

[DagOtto]

Thanks for the reply.

Logical answers for sure.

But it still leaves shooter error mixed into the process of attempting to determine the most accurate bullet shot from one’s system. I’m not talking about selecting the most accurate bullet here, not developing realistic cones of fire for shooting.

Maybe this is just “real world,” and I need to accept that my own shooter error may affect the accuracy of the bullet selection process, but in our effort to develop the most accurate rifles for the most affective terminal ballistics that seems like a cop-out.

Here’s a ridiculous example that exemplifies my conundrum.

You are testing bullets from your new rifle. You shoot two different bullets from the shoulder 100 times each:

Bullet A has a mean radius of .5 inches but one of the hundred bullets lands 8” away from the point of aim so the max spread is 8.5”

Bullet B has a mean radius of 3” with all 100 bullets in that 6” circle for a max spread of 6”.

I’d clearly then select Bullet A as the superior bullet.
Right?

How about using a lead sled for bullet selection testing? I have read that lead sleds can introduce weird harmonics into a system, but would this yield a more true sample of what a bullet can do?

DO

 

[DagOtto]

Typo sorry: should have said-
I AM talking about selecting the most accurate bullet here, not developing realistic cones of fire for shooting.

 

[Formidilosus]

Thanks for the reply.

Logical answers for sure.

But it still leaves shooter error mixed into the process of attempting to determine the most accurate bullet shot from one’s system. I’m not talking about selecting the most accurate bullet here, not developing realistic cones of fire for shooting.

Maybe this is just “real world,” and I need to accept that my own shooter error may affect the accuracy of the bullet selection process, but in our effort to develop the most accurate rifles for the most affective terminal ballistics that seems like a cop-out.

So you want the most precise bullet, but then eliminate the data you don’t like? Thats a cop out.

Here’s a ridiculous example that exemplifies my conundrum.

You are testing bullets from your new rifle. You shoot two different bullets from the shoulder 100 times each:

Bullet A has a mean radius of .5 inches but one of the hundred bullets lands 8” away from the point of aim so the max spread is 8.5”

Bullet B has a mean radius of 3” with all 100 bullets in that 6” circle for a max spread of 6”.

I’d clearly then select Bullet A as the superior bullet.
Right?

It is ridiculous because that is not how mean radius works- you cannot have a 3” MR but a 6” ES. Extreme spread on average will be approx 3.2 times the Mean radius. But, it approx and still won’t tell you what the rifles worst shot is.


You are making this way too hard in a search for a “trick”. Don’t.

How about using a lead sled for bullet selection testing? I have read that lead sleds can introduce weird harmonics into a system, but would this yield a more true sample of what a bullet can do?

DO

Man, unless you are having a seizure behind the rifle, on sand bags you are shooting within the rifles capability. If you are “pulling” shots, you need to fix that and not worry abut tiny differences in group sizes.

As for lead sleds, no- they are terrible.

 

[DagOtto]

Okay, thanks, I appreciate the thoughtful and direct responses.

I’ll utilize the raw data without any tweaking and without using lead sled etc.

My plan is to shoot 2-10 shot groups of each eligible ammo. Then overlay the targets to create one combined 20 shot group. Then I’ll pick the lowest max spread.

I’m hopeful (and expect) that the same bullet will also yield the lowest Mean Radius.

DO

 

[Macintosh]

This is not based on what I know to be factually correct, but it's how I'd be tempted to look at it for my field shooting where shooter error is almost always the largest source of error--you CAN use different figures to serve as a back-check for the data you are using, ie you could apply the ES=3.2x MR principle to test it. Shoot the groups. Calculate both ES and MR. If ES is roughly 3.2x MR, the data might be considered fairly "clean", and if so it would probably not affect the outcome which method you use. If the ES is significantly more than 3.2x the MR, well, maybe you have something going on that you need more data to see whats going on, ie perhaps something is loose or there is significant shooter error. If yu rule out equipment slop and Es and MR consistently arent tracking together, then your data likely isnt clean enough to be nitpicking about bullets to begin with, so in that case I might choose the cheaper option and practice a bunch, and then re-evaluate down the road.

 

[DagOtto]

Thanks for that insight. This seems like a great way to at least see if data is tracking as it should. Of course as previous commentator noted, there is no way to know if an anomaly is shooter or bullet. But this at least might yield an indication that further testing is worthwhile.

And while this doesn’t likely affect the real world hunting efficacy of me or my system nearly as much as lots of practice and good shot placement, I do feel it is warranted to consider these factors when building a new system and testing out new ammo.

I’ll report back to this thread after I shoot the second 10’ shot groups for all 6 or 7 factory loads. I have a feeling the best performer will likely be clear.