Evaluating precision of your rifle

[Falfan2017]

As your tune changes your point of aim changes, plus conditions. In my mind not sure about this, but the thought never occurred to me. Hmmm~m Anybody else do this?

Here’s an example. Seating depth test one is .003 in the lands the next is .006 in. The .006 is the better group but when you overlap them you see that 2 rounds from the .003 group go perfectly into the .006 group with one round expanding it slightly. So this is probably a decent seating depth with a bit of room on each side. Haven’t had a chance to shoot this at 600y with everything being cancelled but it will be interesting to see if it holds up. The 1.812 is .003 in and the 1.815 is .006 in

 

[Burnt Powder]

The downfall of this method is that you are moving the POA/POI within your sample. A 5x5 is not nearly as instructive as a single 25-shot group all shot to the same POA.

When we speak of precision, we really mean what is our statistical confidence that our points of impact will fall within some distance from the point of aim. The military uses the Circular Error Probable idea as the circle that will contain 50% of the points. It's a circle that represents the median error from the point of aim.


As a shooter there are two ways to use the interrelation of confidence and group size. You can either fix the confidence first and then assess group size to that confidence level. Or you can fix a size reference first, then assess the confidence in those terms. But here's the key thing: WITHOUT BOTH DEFINED YOU CANNOT COMPARE.

The reason I took up midrange shooting was because I wanted real data on the actual precision of my rifle and loads. On an NRA target of known scoring rings, I can easily know this data. If I shoot a 200-14x on a sling face, I know with a 20 shot sample that 14/20 are ~sub-moa, so this is 80% confidence. A higher score might take me up to 88% or 92% confidence as X count rises. And in this case, it was 100% confidence of sub-two MOA. But that's only a sample size of 20 shots. Unless you are agg 600 with regularity, you don't have that 100% confidence in reality.

The more difficult method would be to calculate the size of the rings that would contain 90% or 95% or 50% of your shots, or whatever it is you want to use for reference. Either way is valid because it contains both the essential elements of confidence value and error value (group size).

I'm fairly certain that at one point or another, almost everyone on this board as fired a particularly satisfying bughole in the 2s or less. But, given enough shots and attempts, ANY RIFLE can and will do this. It just might take several thousand groups for one to do it or a single attempt for a very excellent rifle.

This is why group size is not only part of the picture, but it's probably the less important part. Without sample size and demonstrated confidence values, the group sizes themselves are next to meaningless. This is why those who point to a single five shot (or worse, three shot) group as demonstrating a rifle's capability are kidding themselves first, and us second.

That’s to anal for me! If I can consistently shoot 5 shot groups on multiple bullseyes as in Benchrest targets. They’re all the same as the first one, and can do it at will, every time I bag up, any day with a few different loads, then I know what I’m dealing with. I’m not a competitive shooter, unless you consider shooting prairie dogs with a couple friends where you get 10 shots or until you miss until the next guy shoots as competition? If I know my rifle shoots 1/2” groups with 5 shots today just like it the second Thursday last month and on New Year’s Day a year ago, it’s an accurate rifle that has a 100% confidence level for me! I know the rifle’s capability, if I miss, it’s not the gun!

Others have other requirements as you described, not most of us. Most people can’t shoot 2 5 shot groups in a row under an inch anyway. I’ve seen a lot of them try, rarely happens. I’ve got a few rifles that will do that, even if I’m not the operator, assuming the shooter is a shooter.

 

[JEFFPPC]

Thanks Falfan2017, sometimes my bulbs a little dim. It could be info with knowing if you load at a match.Knowing a load window with no impact notice would have value. Did you ever try it lat a longer distance and if so did the groups still overlap?

 

[Falfan2017]

Thanks Falfan2017, sometimes my bulbs a little dim. It could be info with knowing if you load at a match.Knowing a load window with no impact notice would have value. Did you ever try it lat a longer distance and if so did the groups still overlap?

I haven’t got a chance to try this one at long range yet. Just did this development at my local short range on Saturday. But in the past when loads made groups like that at short range it held up well at 600. Seems like vertical is the most important thing in short range load development. If you have even .1” of vertical at 100 it’s gonna be good for several inches of vertical at 600

 

[JEFFPPC]

Try that vertical at 1000, it's the name of the game.It has been my biggest challenge coming from the short range game. Even 500 yd groundhog shoots no vertical problem but jump to 1000 and its , wow, where did this come from.

 

[Falfan2017]

Try that vertical at 1000, it's the name of the game.It has been my biggest challenge coming from the story range game. Even 500 yd groundhog shoots no vertical problem but jump to 1000 and its , wow, where did this come from.

Yeah I don’t have any 1k br matches around me but like to try it some day.