Vertical and horizontal spread in load testing?

[DenisA]

Most threads that I read and opinions that I hear, people are always talking about identifying the better loads through the least amount of vertical dispersion in their groups.
In my experience, horizontal dispersion is just as much of a player regarding loads that are NOT tuned properly.

I find that in powder charge testing and seating depth testing, as I move a long a series of increments there will be a pattern where groups Vertical string, then come in gradually and then horizontal string and then come in gradually. The better loads are obviously tighter and mean that when they come back in they're a bug hole rather than open group.

The way that I understand barrel harmonics is that the barrel wil not only vibrate up and down, but also left to right and all other directions.

Would you guys mind putting me on the right track.

Cheers, Denis.

[macguru]

How I see load tuning .........




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[DaveMc]

ha ha - is that blank in the middle the super v or 6?

[ecomeat]

G'day Dennis.
I'd be one of the least qualified to try to answer your Q's in any technical sense, but just a couple of comments.
I test a fair bit here at home, but it's (a) nearly always in the later afternoons so lighting is always a concern with chronograph performance, and (b) there is quite a bit of switching wind to deal with basically every single time I shoot. We are in hilly country and rarely get any periods of no, or little wind.
So after reading the same experienced comments that you have re "vertical" being the thing that matters most, it sort of suited me to start believing it ! If I seriously tried to shoot groups here at 300 or 500 yds or more, I would probably give up and sell everything
At 300 yards out to 500 yards,I only worry about vertical......Coz that's what everyone seems to say, as you point out.
When I can't help myself and I have just got to shoot some "groups" ( to see how I am going, and/or how a load is going) i do it at 100 yards........where the wind effect on my results is way less than it is on my 300 yard range. It's far worse again on my 500 yard range. At 100 yards, it s basically over flat ground, whereas at 300 yds the bullet is probably about 200' high at the halfway point, and at 500 it's over the same valley, plus over a ridge line,then another little valley. Just bloody impossible winds to read with any consistency......... So when I got hooked on F Class about 18 months ago, this focus on vertical dispersion was welcomed by me like a long lost child.
But like you, I keep getting this lurking, deep down suspicion that I am conning myself, and that horizontal dispersion is every bit as critical. I guess I will just have to keep shooting F Class every week till I find out for sure !! Hopefully lots of our successful shooters will add their two cents worth, coz I sure am as keen as hell to read what they all say.
Happy New Year to all, and good straight shooting in 2013.

[macguru]

ha ha , i try to get them all in the middle bit, and its nice when thats smaller than the x ring

I'll try and find a spirograph drawing where all the lines intersect in the middle but i think the hole is an artefact of the system.....

Of course what i meant was that the vibrations in the barrel produce oscillations with a circular component , from the torque, and thats why an out of tune barrel will sometimes produce a ring of shots at the edge of, say the 6 ring, a 'hollow' group.

[Cameron Mc]

This is how I see barrel vibrations.
Effects of gravity influence the vibration of the barrel. This should mean most of the vibrations of a rifle barrel, when fired, are in a vertical plane. Even when static the barrel has the force of gravity acting on it. This is called sag. The horizontal component is neutral in the static condition.
By tuning we try to eliminate the largest component which is in the vertical plane which also hopefully tightens up the horizontal component which should be less in the equation.
Tuning at 100, 300 or 500yds is quite easy as velocity deviation does not play a massive role.
Tuning at 1000yds is where it all counts. Velocity deviation plays a big role in accuracy. I think Dave touched on this in another thread.
I have more input regarding this but would be keen to hear other opinions first off.

Cheers
Cam

[macguru]

cameron, you forget the effect of rifling and newton's third law. There is a circular component whose influence is just as real as that of gravity .....

[Cameron Mc]

cameron, you forget the effect of rifling and newton's third law. There is a circular component whose influence is just as real as that of gravity .....

Correct..... during firing.

Gravity is acting at all times, so the sag of the barrel has to be overcome during firing.

Statics and Dynamics

Cheers
Cam

[Norm]

I have found that when testing, some of my vertical stringing is actually on a slant.
I have also noticed that my rifles with round forends, tends to twist on its front bag/rest as the rifle is fired and the scope tends to end up off level. Other rifles with flat 3” wide forends do not do this to the same extent but still try.
This twisting and flexing of the rifle/barrel indicates to me that load tuning is not as simple just getting the vertical group size/spread small. I can visualize some horizontal component in the mix as well.
How to minimise this component is the question. Any ideas?

[Cameron Mc]

G day Norm

Yes there is a horizontal component. I believe the vertical component is much larger. Especially as the range increases.
The twisting effect is Newton's law at work. Equal and opposite twist of the rifle due to the spin of the projectile. You can minimise this with an offset fore end to aid better tracking.
Tuning is the way to minimise group size. "Tuning" covers many things, starting with the build of the rifle

Happy New Year
Cam

[AlanF]

...This twisting and flexing of the rifle/barrel indicates to me that load tuning is not as simple just getting the vertical group size/spread small. I can visualize some horizontal component in the mix as well.
How to minimise this component is the question. Any ideas?

Norm,

I don't believe that the effect of torque recoil is the same as horizontal barrel harmonics. FWIW, my next stock will have a very low profile fore-end offset about 15mm to the left. This should reduce the twisting, but the energy has to go somewhere - maybe vertical.

On the subject of long range vertical tuning, I'm still looking for answers. It does make sense that velocity variation plays a much bigger part at the longs. Everyone knows how a rifle that shoots good vertical at 300 can be hopeless at 1000. But I think you can still find nodes at the longs - they're just harder to find, particularly if you have inconsistent MV or BC. One thing I wonder about is whether our trend to thicker barrels might actually be counter-productive for tuning - ladder plots tend more towards a straight line. With my barrel block stock, which virtually shortens the 1.25 parallel barrel by about 150mm, my 500 yard ladders are not as obvious as with a conventionally bedded action and thinner barrel.

Alan

[macguru]

I was not talking about recoil, i was talking about barrel harmonics...

even if you bolted the action to a slab the barrel end will sing or oscillate with longitudinal, transverse and torsional waves that make the end move in a spirograph type way. I agree there is more vertical than horizontal but its all happening just the same; as the metal cylinder absorbs all that energy and starts singing, before the projectile has gone more than 10% of the way down the tube.

Somehow the 'nodes' are points where either the muzzle movement is minimal or 'lets go' while crossing the same point all the time... i wish i knew !
it would be great to watch it with a high speed camera...

[aaronraad]

Just need Borden Barrels to come up with a 3D version of their program incorporating barrel twist.

http://www.border-barrels.com/articles/rimfire_accuracy/barrel_vibrations.htm

Good fun to play with anyway.

[DenisA]

This is how I see barrel vibrations.
Effects of gravity influence the vibration of the barrel. This should mean most of the vibrations of a rifle barrel, when fired, are in a vertical plane. Even when static the barrel has the force of gravity acting on it. This is called sag. The horizontal component is neutral in the static condition.
By tuning we try to eliminate the largest component which is in the vertical plane which also hopefully tightens up the horizontal component which should be less in the equation.
Tuning at 100, 300 or 500yds is quite easy as velocity deviation does not play a massive role.
Tuning at 1000yds is where it all counts. Velocity deviation plays a big role in accuracy. I think Dave touched on this in another thread.
I have more input regarding this but would be keen to hear other opinions first off.

Cheers
Cam

Thanks Cameron, I hadn't thought of the effect of gravity and "barrel sag" in this equation but it does make sence that that would contribute to heavier vertical oscillation and then vertical group dispersion.

Another question I have is, most shooters will recommend using a load that gives the least vertical rather than the least horizontal.
Strategically that load that may have a little more horizontal can be blown out either side of the x or 6 ring as the wind and horizontal disp. work together and string sideways.
If a load groups with a little more vert. disp. than horiz. disp. then any wind effect would turn a horizontal slight string into a nice round group still centred on hopefully the X ring..

Therefor I would have thoought that a little more group vertical would be better than horizontal.

Have I lost everyone yet?

[aaronraad]

Check out page 13 or thereabouts:

http://www.dtic.mil/ndia/2008gun_missile/DawsonThomas.pdf

Engage your line of sight with this:

http://www.dtic.mil/dtic/tr/fulltext/u2/a800069.pdf

Then strap yourself in for the history repeating...its the squeezebore that's not so sqeezy:

http://www.dtic.mil/ndia/2009infantrysmallarms/tuesdaysessioniiisiewert.pdf