yeoman

UC -

Many of the groups we talk about and show pictures of are "off target" meaning off POA. Explanations could be:

Sight/scope alignment (physical adjustment)
Sight/scope interpretation (inconsistent eye to reticle distance, for example)

Wind
Flinch (consistent flinch)
Variation in powder measure
Ramrod pressure variations
etc...

There are things which may be consistent on a given day, but not over a string of outings. On one day, I may load 90 grains with a slight bulge to the powder measure, producing a 3" 3 shot group NW of POA. The next outing, my 90 grains is level in the measure, producing a 3" 3 shot group NE of POA. By being consistent (consistently inconsistent?), I have managed 3" groups but varying POI's. Using probability, the variability is in essence averaged. Maybe the wind would be a clearer example. From the left today and I shoot a nice tight group 5 inches right of POA. From the right next time, and the group's 3" left of POA. A statistical result would blend those elements together.

Pglasgow

Yoeman,

If you shoot a 3" 3 shot pattern 2/3 of the time, this means that almost 88% of your shots lie in the 3" circle. I would think, given the vast majority lie in 3" circle, a very minor probability (almost zero)exists that a shot will land outside a 6" circle (target).

I am assuming pristine range conditions and the sights adjusted for group centers at POA (center of circle).

That said, in adverse wind conditions, (which doesn't take much with projectiles of low ballistic efficiciency), the patterns necessarily widen (arising from wind speed fluctuation) and POI of the group centers get shifted (arising from deflection by wind). Easily with PRB, ballets, light weight PBs, this deflection can prevent the impact on a 6" target unless a windage adjustment (sights or POA) is undertaken. In other words, in adverse wind conditions, the probability of hitting a 6" target, without adjusting for wind,can go from almost 100% to almost 0%.

I don't know if this is helping, but you can develop your own probability distribution data if you keep good records of your range time and make sure the data is not dramatically affected by windage. But more important is gaining a sense of how windage is affecting POI at the more distant part of your effectiverange. Hunting in windy conditions can change your strategy, ie where your stand is, or stalking to get the wind in line with your shot.

yeoman

Pglasgow -

What I was describing was a sequence of 3 shot groups, not within a specific 3" circle, but within 3 inches of each other. The individual 3" circles, on successive outings, may be in varying places on the target. Can you find a probablility of 6/6 on a specific 6" circle from this information? I'm not sure.

Pglasgow

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Added: Yoeman, I see I didn't answer the question specifically. I apologize for that. Regarding, a specific 6" circle, here is the best way tolook at it. The specific 6" circle should be centered on the POA. And yes, in virtially windless range conditions,the probability of impact in a specific6" circlecan be determined.

But for field conditions its gets more complicated due to windage. After all, we have to hunt when we can and during a specific time window, during which, we can not pick the weather.

Lets say you load with a 80 grains GOEX and a 270 BB. Lets also say that in pristine wind conditions you have found all of your POI's within 2" of POA. This would be a distribution that would most likely have most 3 shotgroups under 3" and all under 4". Speaking hypothetically of course it would depend on the actual distribution.

It is a better question while hunting to ask, "What level of crosswind has the potential of taking his shots outside of the 6" circle?" Forload andimpact distributionpreviously mentioned,as little as 4 mph will take the majority of impacts out of the 6" circle. Also, the crosswind must be less than 1.2 mph in order to for all to impact within the 6" circle. Also NO impacts will be within the 6" circle in a crosswind of 6.4 mph or greater, and having the potential to miss the intendedpoint of aimby as much as 7"
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Given different range conditions that is what we want to see,specifically, a good grouping whose center is deflected as a result of the existing range condition. This of course an indication of precision, though not necessarily accurate. We like precision because it tells us we can move that precise grouping centerto the POI we want.

Even so, precise accuracy is what we are ultimately trying to achieve. We want no more than an acceptable miss from POA. That way, we can be sure the POI is close enough to the point we are aiming at to get the results we are wanting (lethally shot animal quickly dying).

eldeguello

"I've come to the conclusion that a3 shot "group" only has weight if it is repeatable with consistency."

You are 100% correct! One 3-shot group proves nothing - if your rifle shoots ONE good 3-shot group, it must be able to do it again and again with pretty much the same results each time, or it means nothing. What is important is the AVERAGE SIZE of a numbewr of 3-shot groups fired under the same conditions with the same load as the best one.

However, most of us tend to save the BEST group, me included!

outdoorslover

However, most of us tend to save the BEST group, me included!

Me too!!!! I just threw out my OLD targets from before I tuned the load( I had some 8 inch groups[&:]). They weren't too impressive obviously.

But, as I said,I have shot 3 inch groups for the last 5 range sessions with my good load soI now consider myself consistent. I don't count past experiences orI would be screwed. Everything good takes time.