This is all magnificent information, and I'm studying it very closely, as I'll be doing one for my new 700ADL varmint shortly.
As I've been absorbing all the information, I have a couple questions-
What's "ES & SD"?
I'm starting to understand the principles of the ladder test too, using range to magnify the variances in bullet trajectories to identify the nodes, IE where barrel harmonics are closely similar, identifying a sweet spot in the charge work up.
I'm planning on doing my test with one powder/bullet combination which is known to work well in rifles of similar configuration, in hopes that I'll get it dialed in fast.
they are the measures of the differences in velocity, shot to shot, for the load your testing/using.
extreme spread is the maximum and mimimum velocities of that load, or more precisely, the difference between them measured in fps.
Standard deviation, is more complicated, its worked out from the average velocity of 5 shots of a particular load, and the standard deviation your most likely to get above or below this average velocity. I never use SD and dont really see the value of it... i simply look at ES because its easier to understand and correlates to a long range ladder test in that your lowest impact has the lowest velocity and highest impact the highest, so you can see the end result of the load physically on the target and you will know within what vertical range your shots might fall, at distance, in a hunting situation.
Standard deviation, is more complicated, its worked out from the average velocity of 5 shots of a particular load, and the standard deviation your most likely to get above or below this average velocity.
Effectively speaking, the more consistent the ammo, the more consistent the standard deviation, equals smaller groups...in theory...based on most consistent velocities causing less variance between high and low velocities in the batch of loads...which leads into other aspects of reloading like neck tension, powder consistency, bullet consistency in mass and form, and the ballistic coefficient...
I think that was a crucial piece of information I have been looking for to help solidify everything I've been reading about the ladder test and bringing the best, most consistent loads to the bench...
Thanks a bunch!
Now, to ponder it all, and toss it about in my head...
I feel like a little kid that found his first potato bug!
Every time I've shot a ladder test over a crony it has been an "aha" moment! I find what the max load for that particular rifle then load down from that every .5 gr three shots. I end up with 15 rounds then I color each set a different color then shoot them round robin over a crony @ 300 or 600 yrds. The info from the target and the crony combined will most likely almost jump out and grab you!!
"Pain is weakness leaving your body"
Ok, I get most of that.
I'm thinking that, by using a marker to distinguish each of the varying loads, you're able to discern more readily where your nodes are, as illustrated by your grouping.
When you find the harmonic balance of the load with the barrel, you find a lateral grouping as opposed to vertical stringing which indicates a variance in velocity.
That info, correlated with consistent chronometer readings, helps find the center of the sweet spot. So, getting that extreme consistency round to round is crucial to getting the best results from each shot fired for the test is the goal achieved by taking extreme care in case prep, powder measuring, concentricity, bullet seating depth, and so forth, are all considerations in getting that Holy Grail bughole at long range....
Sorry for rambling....I'm having an extreme AHA! Moment, and making sure I'm understanding each aspect thoroughly....
Ya, coloring the bullets and shooting through card board lets you shoot the entire test at a steady pace in the closest to same conditions with out running back and forth marking your target. It's actually very fun to do cause of all the feed back you can have in a short time. I only do this to find a powder combo, prior to this I do a primer test and seating test to find the best primer and seating depth for a particular situation.
"Pain is weakness leaving your body"
Good velocity consistency is only important at long range where the vertical variation becomes a problem due to velocity alone. At short range, you will not be able to disern any vertical variation from velocity alone. This is purely from the ballistic drop of the projectiles at different velocities and the effect becoming more amplified as the distance increases. It has nothing to do with barrel harmonics or any other part of the organic dispersion within the rifle system.
You CAN have good accuracy at short range, with big velocity variations.
You CANNOT have good accuracy at long range with big velocity variations.
Although they often improve together, accuracy and velocity are 2 different things. accuracy is internal, velocity is external.