Should have a lot more vertical

[P. Octo]

Sorry, I can't turn the picture upright, but my question is why not a lot more vertical?
I was shooting a LV Krieger 6PPC barrel, Berger Column, moly coated, on top of 29.8gr of V 133 at 100 meters. Wind was about 2.5 m/s from 1 to 3 o'clock with occasional gusts at 5 m/s. As I was testing the Column in this barrel I didn't hold for vertical and on that particular target I held a tad less than the 1/8" dot laterally. Now, The Labradar gave:

3412 ft/s
3343
3330
3340
3451

With such a huge difference in velocity I'd have expected a ladder! Also, strange enough to me, the velocity at 25m didn't reflect the differences at V1; the 3451 and the 3330 difference of 121 ft/s dropped to about 33 ft/s. No explanation. The cases had been through a few matches but annealed on the AMP machine and checked on the ICC, trimmed, etc., the work... Powder had been weighed and put in tubes; temperature was 13°C (55°F), humidity 39%.
I was tempted to suspect the Labradar readings of the V1 shots (reading the blast?) but that seems farfetched.

[Pbike257]

It doesn't really matter... That load doesn't work for your rifle. That group should be half that all day.

[alinwa]

Sorry, I can't turn the picture upright, but my question is why not a lot more vertical?
I was shooting a LV Krieger 6PPC barrel, Berger Column, moly coated, on top of 29.8gr of V 133 at 100 meters. Wind was about 2.5 m/s from 1 to 3 o'clock with occasional gusts at 5 m/s. As I was testing the Column in this barrel I didn't hold for vertical and on that particular target I held a tad less than the 1/8" dot laterally. Now, The Labradar gave:

3412 ft/s
3343
3330
3340
3451

With such a huge difference in velocity I'd have expected a ladder! Also, strange enough to me, the velocity at 25m didn't reflect the differences at V1; the 3451 and the 3330 difference of 121 ft/s dropped to about 33 ft/s. No explanation. The cases had been through a few matches but annealed on the AMP machine and checked on the ICC, trimmed, etc., the work... Powder had been weighed and put in tubes; temperature was 13°C (55°F), humidity 39%.
I was tempted to suspect the Labradar readings of the V1 shots (reading the blast?) but that seems farfetched.

P. Octo....

Your observation is accurate and your question is a wonderful one. And there IS a solid and repeatable explanation.

What you are seeing is a phenomenon called "velocity compensation" which is the rock-solid basis of the technique known as "tuning"......your lower velocity rounds are on a different trajectory that your higher velocity rounds.

These different trajectories are generated by the flexing of your rifle barrel. The barrel flexes such that the slower rounds are launched at a higher angle than the faster bullets and they converge at your measured range.

It's like throwing a slower ball and a faster ball to the same catcher.

You have empirically discovered exactly why this "tuning" technique is yardage specific. I have a setup where one can shoot a group thru a target at 100, 200 and 500yds...... SAME GROUP..... and it's easy to show that that same group at 200 would be tall and at 500 yds very tall.

[P. Octo]

Thank you for your post. I'll check it at 200. Your theory seems to fit the facts and answers my questions.

[alinwa]

Incidentally this is also specifically why for the last 20yrs certain successful benchrest guys have been saying "I always tune at 200 because then its good for both yardages"

Draw it on paper to see it clearly, sideview of the two trajectories.

This is why thrown charges easily win at 100-200 and are a total cockup at longer ranges like 600-1000 (even though there are still plendy range-rats who velocity tune at 600-1000 and can still get good results even with high ES...... velocity compensation WORKS!!.....)

As far as what the becigneuel fellow is saying about your load sucking, I have no comment. I'll leave that sort of verbiage for the "pros" .... maybe he or his dad'll elaborate for you but I wouldn't count on it

[P. Octo]

I always thought that if it was well stabilized at 100, it should still be good at 200; your remarks give me pause for thoughts. And I will try the same set-up at 200. Yet, what still bothers me is why such gap in velocities when I took care of checking as many parameters in the cases as I could, including the pressure to seat bullets.
I don't pay attention to posts that are irrelevant as they don't address the question.

[Al Nyhus]

Before getting too far out on this, find out the chronograph manufacturer's stated margin of error. -Al

[John VM]

As Al Nyhus says, Chronographs are not always that accurate. It is in tune and shooting well. See how wide the tune window is and mark everything down.

[OliveOil]

Hi Philippe,

You may wish to pick a single case, anneal it, check length, headspace and all, then shoot it five time in a row. This could give an idea of the chrono variation. Getting the same StdDev or ES again would point to the chrono. You will of course warm the barrel up the same way before shooting the "record" round.

Keep in mind electronic components and circuitry need "some time" to get heat stabilized. You may check in the Labradar leaftlet if there is anything writen about winter use or time to warm up.

[alinwa]

I have 11 chronographs ranging from Magnetospeed to a pair of Oehler 43's.... the last of which I bought from Dave Tooley. My understanding is that Dave is a fairly fart smeller and that the Oehler may have been connected with or used for for military testing projects under "Agencies Not To Be Named or I Weel Haff to Keel You" and therefore must be considered trustworthy

cuz David aitn't dead

I have a Labradar which features quite prominently on my youtube vids.... kindofa' love/hate deal there.

The reason I consider this information to be relevant is that I shoot them head-to-head and in concert.

I have a picture here on BRC from BBtB's, an image of three chronos mounted on a board in a line...

I've fired enough rounds thru 3 chronographs at once to state that bullets are slow, easily plotted and that "chronograph error" is a non-issue.

And I've plotted enough sine-wave tuning graphs (again, there's pix here on BRC) to have documentation of groups VS velocity changes...it's REAL f'r real

Incidentally I just recorded an episode last week wherein I'm shooting 1002gr bullets at 1000fps and you can SEE where 25fps=1" drop at 100yds!! I'm having trouble getting low ES with this setup and 75fps velocity spread documented shot-by-shot results in groups 3" tall! Too Much Fun! Checking the chrono then looking down to find a bullet completely in line with the velocity profile makes me all warm inside.



25 feet per second equals one inch of vertical on this setup.....and if someone pisses me off enough I'll go film it in real time (that's what started my channel almost 3yrs ago LOL)

I just got my Genesis back from Japan today.... might go down and run 'er out to 600..... except I won't be able to keep the vertical on a sheet of plywood!!

[alinwa]

BTW, if you want the ES to go down to under 10fps you'll need to spend equiv $500USD for a scale that registers kernels.

I routinely get 50BMG's down near that.....size don't matter

[P. Octo]

Hi Philippe,

You may wish to pick a single case, anneal it, check length, headspace and all, then shoot it five time in a row. This could give an idea of the chrono variation. Getting the same StdDev or ES again would point to the chrono. You will of course warm the barrel up the same way before shooting the "record" round.

Keep in mind electronic components and circuitry need "some time" to get heat stabilized. You may check in the Labradar leaftlet if there is anything writen about winter use or time to warm up.

Good idea! I'll do that.

[P. Octo]

"I have 11 chronographs ranging from Magnetospeed to a pair of Oehler 43's."
I had been thinking of taking my Oehler out of retirement to check it along the Labradar; I already sold the Magnetospeed. I could do that when trying OliveOil's suggestion of shooting a dedicated case 5 times in a row. I am aware that shooting it changes it every time.

[Al Nyhus]

Regardless of what anyone's chronograph shows, this is what makes the difference when it comes to 'on target' accuracy.

In fact, your gun demonstrated exactly this.

Good shootin' -Al

[P. Octo]

Thank you all for your comments & suggestions.