Positive compensation at 100 yards.

[Ccrider]

Does trajectory affect group size? Are you saying that my groups at 100 shot using my 1000 yard zero will be different size than my group at 100 using 100 yard zero? This is assuming all other factors except for trajectory are the same .

 

[davidjoe]

Does trajectory affect group size? Are you saying that my groups at 100 shot using my 1000 yard zero will be different size than my group at 100 using 100 yard zero? This is assuming all other factors except for trajectory are the same .

The barrel vibrates differently, with and without the full force and effect of gravity along its horizontal length.

Granted, the difference in barrel angle between 100 and 1,000 yards is very small.

However, the difference between almost straight up, and nearly horizontal is quite noticeable, trust without trying to verify this .

I would venture to say that none of us would think our target barrel contoured rifles have sufficient build solidity or tenon rigidity, if we lived in a hypothetically wide open space where we hypothetically have shot a rifle, very nearly straight up.

I have imagined such a scenario and as a result, for years shim a compressible material between my barrel and stock fore end to mitigate vibrations.

 

[CharlieNC]

I have imagined such a scenario and as a result, for years shim a compressible material between my barrel and forehead to mitigate vibrations.

Vibration is your friend, and is what provides positive compensation! But we have not advanced sufficiently to understand the proper frequencies and how to harness them for maximum benefit.

 

[davidjoe]

Vibration is your friend, and is what provides positive compensation! But we have not advanced sufficiently to understand the proper frequencies and how to harness them for maximum benefit.

I’ve been an audiophile an equally long time, and so I am compelled to agree with you .

 

[seymour fish]

As I understand the geometry, the parabola that decribes a bullet's trajectory at 100 yard is not simply a fractional segment or sub-segment of the parabola that describes its trajectory at 1000 yd. In other words, the 100 yd parabola will not perfectly overlay the first 100 yd (or any other portion) of the 1000 yd trajectory. That would seem to be at least part of the explanation why loads developed at 100 yd might not be optimal at some other distance.

One observation I would make regarding the 1000 yd/100 yd group data presented above is that the groups at 100 yd are not even close to what I would consider "good" groups for a well-tuned F-Open rifle, ranging from about 0.8 to over 1.0 MOA. The possible exception to that statement would be the 100 yd target from the final pair (B41), but even that 100 yd group is still larger than 0.5 MOA. Thus, I think trying to infer anything from the shape of the 100 yd groups that could be used for comparison to the 1000 yd group shape would be difficult. Because of the relatively large 100 yd group size, I suspect there is too much uncertainty in 100 yd group shape/shot placement to reliably compare them to the 1000 yd group shapes. It may even be possible that the resolution of the e-target system may come into play with the 100 yd groups. In other words, there are potentially a number of sources of errort that make interpreting the shape of the 100 group more challenging. Having said that, the final pair of groups at 1000/100 (B41) are both similar in shape, both being generally roundish. Further, had it been centered on the target face, the 1000 yd B41 group would have been fully contained within the 10-ring, with very close to a 50% X-count. From his statements, Tod has obviously seen a lot more of these targets than he posted above, which can make interpretation of any trend much easier, so I fully accept his assessment of the results. Nonetheless, I think it would be interesting to see how a load that shot much tighter at 100 yd (i.e. 0.25 MOA or less) might behave at 1000 yd.

In any event, one of the issues we have to deal with when assessing groups at 100 yd is one of resolution and/or measurement. We can add to that that the bullet hole diameter represents a much larger proportion of the group spread than it does at 1000 yd. Increasing the distance is an easy way of "stretching out" the Y-axis, thereby effectively improving resolution. However, that also increases the potential effect of the ambient weather conditions on bullet trajectory. The major benefits of carrying out preliminary load development at 100 yd are minimizing any conditional effects, and that most shooters have ready access to a 100 yd range. Not everyone can do load development at 1000 yd. So I will end by circling back to my inital statement regarding the different shapes of the bullet trajectories (parabolas) at 100 and 1000 yd. If one could do the kind of analysis Tod has shown above and reliably detect a certain group shape at 100 yd that was associated with a load known to be tuned really well at 1000 yd, then it should still be possible to get the load pretty well developed at 100 yd. Even if the 100 yd group wasn't good/tight/tiny, as long as it had a recognizable and reproducible appearance, it could be used to tune a load that would shoot well at 1000 yd. I don't think anyone would argue against the benefits of doing load development at the distance to be used in matches, but not everyone has access to a 1000 yd range for load development, and/or the e-target setup to facilitate that process. The more one can do at the distance/range they do have access to, the better off they will be. This also raises the question that if groups fired at 100 yd offer little to no insight into optimizing groups at 1000 yd, is there some other intermediate distance, such as 200 yd, or 300 yd for example, commonly available to most shooters, where the results do better match those obtained from the same load at 1000 yd?

To simplify, tune for best load at 1000, with some “forgive” built in re: ES, wind sensitivity. Shoot it on paper at 100. Notice group shape.

 

[CharlieNC]

I’ve been an audiophile an equally long time, and so I am compelled to agree with you .

Interestingly, audio software fed from the microphone jack on a pc is more than adequate to analyze an accelerometer signal, as sound frequencies of interest are faster than barrel times.

 

[Alex Wheeler]

Oh boy

 

[gunsandgunsmithing]

Oh boy

Me too! I'll probably stay out of this.

 

[lawman29]

One observation I would make regarding the 1000 yd/100 yd group data presented above is that the groups at 100 yd are not even close to what I would consider "good" groups for a well-tuned F-Open rifle, ranging from about 0.8 to over 1.0 MOA.

The first four targets are ladder tests, not groups.

 

[F Class John]

Tod thanks for taking the time to share your findings. You spend more time behind a gun testing than most, all at a private range where you can do some cool things like this test which really can't be done at public ranges. You certainly don't have to share anything with the general public but I think your multiple National wins, World Championship Gold, SWN wins plus countless other local, state and regional wins speak to your ability which is far above most, especially when it comes to testing for precision, rooting out the noise and finding what really matters so it's appreciated.

Someone I was talking with about this said it the best, "the simplest and most interesting result is that a sub 1” group at 100 ending up almost 30” tall at 1,000, with interesting subset groups and how those compare between 100 and 1000yds." I would agree and it's definitely interesting when viewed like this.

Everyone will have their own takeaway from this but seeing real data like this helps, even if it's just to confirm whatever your hypothesis was going it. I'm a believer in 100yd testing but as Ned said, I've done enough that I'm comfortable knowing what I'm looking for but I still always work to confirm best I can at actual target distances when I'm able to get to those distances.

I also understand what you were trying to accomplish here which isn't as black and white as it appears and appreciate you took the time, energy and components to do it if for no other reason than to cross it off your 'does it matter or is there a relationship' list.

 

[tom]

I second that Tod, thank you for sharing.

Tom

 

[jackieschmidt]

What I did learn is, groups at 100 yards are almost useless as an indicator of bullet grouping at 1000 yards.

and visa-versa.

That is, if you look at it from a Short Range Competitor‘s perspective in what constitutes a competitive grouping, (ie agging) capability.