Is this a good ladder test?

[LynnJr]

Geoff
I don't want you to take this the wrong way but you most certainly are wrong.

I don't know what you are talking about with regards to case volume and node width but there is most certainly a correlation.
Ask any precision shooter using a 6PPC,6BR or Dasher how wide there accuracy node is.It is just that simple.They will tell you right around 0.5 grains wide.

Now go ask anyone shooting longrange with a larger case how wide there node is.Again it is just that simple.A 300 Weatherby or 300 Ackley would be atleast 1.5 grains wide.

On the barrel needing to be at or near the top of its travel you are once again wrong.It just needs to be traveling upwards.If it is traveling downwards the slow shots and fast shots will not group together and the groups will be terrible.The term is called convergence and you don't get it on a downward traveling barrel ever.

On putting the node at the muzzle this can't be done with a naked barrel at all ever!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
You would need to add weight out in front in order to put a node at the crown and that is exactly how tuners work on rimfires or centerfires alike.
.
You can also put a tensioned tube over the entire barrel so it whips in the middle and both ends are more or less rigidly fixed.These tensioned barrel guns have shot very well over the years.

WhiteRabbit
If you are from the bay area you are probably familiar with Lawrence Livermore Laboratory? If so you can see the work on barrel harmonics done by Al Harral here. http://www.varmintal.com/amode.htm
You can also visit the Border Barrels website and look at the Positive Compensation thread written by Dr Geoffrey Kolbey.
This is not nitpicking this is actually what happens.
A slower shot is in the barrel longer than a faster shot.If the muzzle is rising the crown will be at a higher elevation when the slower shot leaves than it will be when the faster shot leaves and the two bullets will converge on the target.
A barrel at rest will have droop in it and when it is fired we only care about the vertical plane as it rises.
If the barrel is in a downward motion the faster bullet would leave first while the departure angle was xxx degrees.The slower bullet is once again in the barrel longer so the barrel would move farther down with the additional time and the departure angle would be even greater ruining our groups by creating exaggerated vertical dispersion.
The optimum charge weight test is simply a round robin method requiring an excessive amount of rounds to be fired top achieve the same results as a ladder test.

[Justintoxicated]

Vertical stringing is almost entirely controlled by pressure variations round to round UNLESS the barrel harmonic is entirely vertical which is luck of the draw thing from rifle to rifle (or barrel to barrel).

Not for me, it's usually just me that causes stringing

I'm confused at what was said though? I thought the ladder was just used to find a starting point, then you can fine tune the powder charge and maybe seating depth assuming that your not shooting a semi auto.

[LynnJr]

When doing a ladder test stick to the 1% rule so you don't skip right over the accuracy node.In a case like the 223 or 6BR 0.2-0.3 grain increments will do.
On larger cases like the 300 Weatherby use 0.6- 0.7 grain increments.This is important and from the earlier responses it is often overlooked and will cause problems in identifying your node(s).

Now load 3-4 rounds at your minimum charge with the bullets seated to the full jam length.The full jam length is the longest length you can load too before the closing of the bolt pushes the bullet back into the case.Neck tension will affect the length so make sure you use atleast 0.003 neck tension.

Now load up your incremental charges and use that same seating length.
At 100 or 200 yards sight your rifle in using the lightest loads and start firing the incremental charges at the same aiming point.
You can use a separate target to plot your hits.
You stop firing when you reach pressure signs.
You will see your shots climbing vertically as your powder charge is increased then they will stop climbing for a few shots and start climbing again.Your accuracy nodes will be the shots with the least amount of vertical for a few shots.
If you keep going you will usually see a second node at or near your max load.This is not the book max load but your rifles max load which will vary based on freebore and projectile used.
If you keep going the climbing will continue but it will be exaggerated.If you were seeing 1/8 inch between shots in a safe region of the test you might see 1/2 inch or more when you reach to much pressure.Don't go any further.

Now you are looking at your target and you notice 2 consecutive shots without much vertical.Lets say 24.7 and 24.9 grains as an example.
You can pick 24.8 grains and load up 20 rounds.
Shoot a 3 shot group and back your seated bullets up 0.005 inches and shoot another 3 shot group.
You repeat this until you find your best grouping.
You can now go back and start lower than 24.7 at 24.6 and you can also go to 25.0 and start shooting 3 shot groups.
The reason you can go a little lower and higher is because you used the 1% rule so you already have 24.5 and 25.1 on your target.
By shooting the entire range or node window you will find your sweetspot.

You can now adjust the seating depth in 0.001 increments until best accuracy is achieved.Again this gives you 0.004 on either side of your previous groupings.

If you happen to have your own reamers you will find out very quickly that once you have the correct seating depth and powder charge there will be very little change barrel to barrel.
Good Luck.

[GeoffLinder]

Geoff
I don't want you to take this the wrong way but you most certainly are wrong.

I don't know what you are talking about with regards to case volume and node width but there is most certainly a correlation.
Ask any precision shooter using a 6PPC,6BR or Dasher how wide there accuracy node is.It is just that simple.They will tell you right around . grains wide.

Now go ask anyone shooting longrange with a larger case how wide there node is.Again it is just that simple.A 300 Weatherby or 300 Ackley would be atleast 1.5 grains wide.

On the barrel needing to be at or near the top of its travel you are once again wrong.It just needs to be traveling upwards.If it is traveling downwards the slow shots and fast shots will not group together and the groups will be terrible.The term is called convergance and you don't get it on a downward traveling barrel ever.

On putting the node at the muzzle this can't be done with a naked barrel at all ever!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
You would need to add weight out in front in order to put a node at the crown and that is exactly how tuners work on rimfires or centerfires alike.
.
You can also put a tensioned tube over the entire barrel so it whips in the middle and both ends are more or less rigidly fixed.These tensioned barrel guns have shot very well over the years.

WhiteRabbit
If you are from the bay area you are probably familiar with Lawrence Livermore Laboratory? If so you can see the work on barrel harmonics done by Al Harral here. http://www.varmintal.com/amode.htm
You can also visit the Border Barrels website and look at the Positive Compensation thread written by Dr Geoffrey Kolbey.
This is not nitpicking this is actually what happens.
A slower shot is in the barrel longer than a faster shot.If the muzzle is rising the crow will be at a higher elevation when the slower shot leaves than it will be when the faster shot leaves and the two bullets will converge on the target.
A barrel at rest will have droop in it and when it is fired we only care about the vertical plane as it rises.
If the barrel is in a downward motion the faster bullet would leave first while the departure angle was xxx degrees.The slower bullet is once again in the barrel longer so the barrel would move farther down with the additional time and the departure angle would be even greater ruining our groups by creating exaggerated vertical dispersion.
The optimum charge weight test is simply a round robin method requiring an excessive amount of rounds to be fired top achieve the same results as a ladder test.

I never said that the barrel needs to be at the top of it's travel. I said it needs to be at the end of it's travel, whether that be up or down, the stop point (end of travel = dwell point where motion arrests momentarily) where the barrel is at rest is what I mentioned.

Of course there is a correlation to charge weight and node, charge weight controls velocity (case volume being same) and "velocity" controls barrel resonance "versus" muzzle exit timing of bullet. What I did say was that charge weight "versus" case capacity (ratio) is not the controlling factor in node width, the barrel resonant frequency is the controlling factor. The higher the resonant frequency (stiffer the barrel) the shorter the vibration cycle and therefore the narrower the dwell time and the less the harmonics effect things (nodes are narrower, amplitude is reduced and rounds will exhibit less radical dispersion if they leave the barrel while it is in motion).

Yes, a node "can be" described as being so many parts of a grain wide, this is because the charge weight controls velocity and velocity factored into exit timing factored into resonant frequency of barrel (think of the barrel as the conduit the shockwave travels in) determines node width. Charge weight is a control factor, "not" the reason for this.

Yes, a downward motion is worse for stringing IF the round leaves the barrel while it is moving. The point of a node is to have low SD and therefore time the average so they ALL leave the barrel within the dwell range. Having bullets leave the bore while it is moving is a FAIL of finding a node. If you do so and accept the lower level of stringing an upward motion during exit provides then you are settling for less.

BTW, I defy you to tell me with absolute certainty which direction a barrel was moving for a specific dwell node you find unless you are using laboratory grade test conditions and then running statistical regression analysis on very large sets of tightly controlled test results. Remember, barrels DO NOT always vibrate in a vertical plane, or in a straight line! That is a fantasy world assumption. A barrel can just as easily have a completely horizontal vibration direction as it can have a vertical or even a diagonal one.

[LynnJr]

Geoff
A bullet exits at a given amount of time so yes we do know were the crown was at at the time of bullet exit and you are kidding yourself if you think your loads are best with a stopped muzzle or at maximum dwell.

I included Finite Element Analysis in my last post showing exactly how a barrel reacts to firing and the bullet is long gone way before any resonance ever takes place.

As an engineer you should be able to view the provided data and interpret what it is saying.Higher velocity shots exit early while pointing lower at the target but drop less in reaching the target.
Lower velocity shots exit later while pointing higher at the target but drop move in reaching the target.
You want the barrel moving in a positive direction at the time of exit or it won't compensate for velocity extremes.

You will see know agreement at all that a barrel on the downward cycle will shoot even at a anti-node or maximum dwell.This is in the work by Geoffrey Kolbey at Border Barrels and also Al Harral's work.

I will link you to his tuner work for a better description.

http://www.varmintal.com/apres.htm

Notice that a barrel moving downward produces a 0.7642 group while a barrel moving upward reduces that group size by 67%.
Please take the time to read both links provided earlier.
Respectfully
Lynn