Testing & Tuning & Tooling & More - Bullet BC testing

[Ahhnother8]

Tod Hendricks thread on positive compensation reminded me of a similar test that I last did in 2021. I set up two Shotmarkers much like Tod did. One was on the top of the 900 yard firing line and the other on the 1000 yard target, as normal. One photo is of the “picture frame target” that was 100 yards away. The bullet simply passes through the empty frame. I was doing a tuner test, but also simultaneously testing the quality of my bullet sorting/manipulating. There was only a mild breeze that day. What really stood out was that once a bullet departed on a given trajectory, it continued on that trajectory. The size and shape of each 1000 yard group is quite similar to the size and shape of the corresponding 100 yard group. From that observation, I would somewhat comfortably do load testing at 100 yards and expect similar results at 1000 yards, IF the bullets all have the same BC. Though one may end up on a very narrow node. Personally, I do ALL load testing at 1000 yards, but not everyone has that luxury. Just food for thought, and your mileage may vary.

 

[ricco1949]

Amazing correspondence.

 

[CA_Shooter]

Yes very similar from 100 to 1000

 

[mfendley]

Tod Hendricks thread on positive compensation reminded me of a similar test that I last did in 2021. I set up two Shotmarkers much like Tod did. One was on the top of the 900 yard firing line and the other on the 1000 yard target, as normal. One photo is of the “picture frame target” that was 100 yards away. The bullet simply passes through the empty frame. I was doing a tuner test, but also simultaneously testing the quality of my bullet sorting/manipulating. There was only a mild breeze that day. What really stood out was that once a bullet departed on a given trajectory, it continued on that trajectory. The size and shape of each 1000 yard group is quite similar to the size and shape of the corresponding 100 yard group. From that observation, I would somewhat comfortably do load testing at 100 yards and expect similar results at 1000 yards, IF the bullets all have the same BC. Though one may end up on a very narrow node. Personally, I do ALL load testing at 1000 yards, but not everyone has that luxury. Just food for thought, and your mileage may vary.

This was an amazing test (and great shooting btw!) and I appreciate you posting the results. I find it interesting that there were a number of groups with a tighter grouping at 1000 than at 100. I believe this is an indicating of the measurement accuracy of the shot marker system, and it is something - in all measurement systems - than is often overlooked. We tend to generate theories for why things happen, when it is due to an error band that we neglect since we cannot see and in many cases, measure.

 

[urbanrifleman]

Incredibly clever. Real world data.

Those are some tiny groups. Thank you for sharing.

 

[Forum Boss]

This is noteworthy. I don't have the benefit of a Shotmarker, but I nearly always found that loads with three-shot groups under 0.2" at 100 nearly always shot very well at 600 yards.

 

[K22]

Interesting thread - thanks for sharing.

While I don't shoot at those distances, the concept is thought provoking. I am a strong advocate of testing concepts and assertions for yourself rather just accepting those claims. This is even more important today with all the claims being made on the net, some of those which are bizarre.

I do all my load development at 100 yards basically because that is the distance that the best bench facilities are available to me. Also, this distance minimizes shooter error, wind and mirage effects which helps to identify the best load. Judging from my field results from varmint / predator hunting, this seems to work quite well but I am only shooting at distance of 300 yards and under.

 

[CharlieNC]

I think it would be expected that the results at 900yd would not be significantly different than 1000yd because the effect of the harmonic cycle would have already occured at a much shorter distance and therefore the relative trajectories would be set. And the compensation which occurs depends on the the particular charge weight chosen relative to the where the barrel harmonic is within the cycle.

We know faster bullets will drop less. The point of compensation is to find the charge where the barrel is on an upswing during the harmonic cycle, whereby you are essentially pointing higher with slower bullets to offset the velocity drop. Likewise an unfortunate charge weight could give the opposite if the barrel is on a downswing and pointing lower for a slower velocity, thus magnifying the velocity differences.

In other words the expected result for trajectories depends on the charge weight, as exemplified by higher velocities hitting lower on a ladder test. Now shooting a simple ladder test through 100 and 1000yd targets would be quite informative.

 

[Ahhnother8]

In other words the expected result for trajectories depends on the charge weight, as exemplified by higher velocities hitting lower on a ladder test. Now shooting a simple ladder test through 100 and 1000yd targets would be quite informative.

Based upon my experience, a ladder test would show exactly the same results at 100 and 1000. Although at 100, the bullet holes would mostly be stacked upon one another, unless some windage was added to each test group, to also separate them horizontally. Once the bullet leaves the barrel on a given trajectory, it stays on that trajectory all the way to 1000, as exemplified by the targets that I posted above. I think...

 

[JEFFPPC]

Interesting to see it tested. My only question is why anyone would think it would be different.Thanks for sharing.

 

[DocBII]

JEFFPPC,

Bullet enters a turbulent trans-sonic range or goes subsonic. Seen it happen with .223 caliber rounds out of a plain .223. Wonderful results to 8-900 yds, falls out of the sky or all over the target @ 1k. 4' round target.

YMMV,
DocBII

 

[dgeesaman]

Interesting to see it tested. My only question is why anyone would think it would be different.Thanks for sharing.

I’ve heard it said to expect to triple the group size (1.5x in moa) for every doubling of the distance. Certainly things like velocity ES, wind variance, and ballistic coefficient variance play strongly into that added dispersion, and LRBR shooters have been shaving down on those inconsistencies for years with some success.

I’m mostly impressed that this load test showed the added dispersion could be so small.

 

[HTSmith]

Now shooting a simple ladder test through 100 and 1000yd targets would be quite informative.

I'm thinking that is what he did.......the 900 yard firing line would be 100 yards from the 1000 yard firing line. I may be misunderstanding

 

[CharlieNC]

I'm thinking that is what he did.......the 900 yard firing line would be 100 yards from the 1000 yard firing line. I may be misunderstanding

I'm speaking of targets at 100 and 1000, not 100 apart. This would address the numerous reports that the accuracy node is different depending upon distance.

 

[Ned Ludd]

Interesting to see it tested. My only question is why anyone would think it would be different.Thanks for sharing.

Another way of asking the exact same question is why should the optimal tune of a load vary with distance, let's say between 100 yd and 1000 yd as shown here, or between 600 yd and 1000 yd? Many shooters here apparently believe that it does, but a comprehensive explanation of why that should happen is lacking, IMO.

Based upon my experience, a ladder test would show exactly the same results at 100 and 1000. Although at 100, the bullet holes would mostly be stacked upon one another, unless some windage was added to each test group, to also separate them horizontally. Once the bullet leaves the barrel on a given trajectory, it stays on that trajectory all the way to 1000, as exemplified by the targets that I posted above. I think...

Like you, this is what I have always observed and believed to be true. However, if the optimal tune of a load changes with respect to distance as many here believe, that would challenge this way of thinking.

 

[Bottom Fodder]

Thank you for sharing, I do all my testing / development at 100 and match shoot out to 1k and I’m happy doing it my way

 

[newbieshooter]

I'm thinking that is what he did.......the 900 yard firing line would be 100 yards from the 1000 yard firing line. I may be misunderstanding

I'm speaking of targets at 100 and 1000, not 100 apart. This would address the numerous reports that the accuracy node is different depending upon distance.

The OP stated he put a ShotMarker out @ 100 yards (empty frame) and another at 1000.

 

[JEFFPPC]

Another way of asking the exact same question is why should the optimal tune of a load vary with distance, let's say between 100 yd and 1000 yd as shown here, or between 600 yd and 1000 yd? Many shooters here apparently believe that it does, but a comprehensive explanation of why that should happen is lacking, IMO.


Like you, this is what I have always observed and believed to be true. However, if the optimal tune of a load changes with respect to distance as many here believe, that would challenge this way of thinking.

Unless you find a 1000 yard tunnel that's a hard one to pin down. Conditions.....the great equalizer. Sometimes with available facts there is no explanation, only conjecture.

 

[lawman29]

I'm speaking of targets at 100 and 1000, not 100 apart. This would address the numerous reports that the accuracy node is different depending upon distance.

Charlie read it again and again until you get it. The 900 yard FIRING LINE and the 1000 yard TARGET.

 

[Ned Ludd]

I cut and pasted each pair of test groups from the OPs images side-by-side into a new file to make direct visual comparison a little easier so viewers can draw their own conclusions about the relationship between groups at 100 and 1000 yd. The group sizes/shapes are not perfectly identical between 100 and 1000 yd, but as a whole they're pretty close. #4 and #8 appear to exhibit the greatest disparity in group size/shape between 100 and 1000 yd, which could result from shot #10 and shot #22, respectively, dropping farther out of the group at 1000 yd, but I can't be 100% certain about that as the shot numbers are not marked on the 1000 yd target image. IMO - most of the relatively subtle differences between the groups could readily be explained collectively by 900 yd worth of conditional effects and/or detection variance at one ShotMarker relative to the other. I'll add my thanks to @Ahhnother8 and @Tod Hendricks for posting their two-target results and initiating this discussion. It appears as though the two-ShotMarker setup may be very beneficial for testing/analayzing external ballistics in a manner that was previously much more difficult for many shooters to carry out.