Re: OCW Method Works!
Umm, yeah, it works..........
Barrel Harmonics are a given. You simply can't deny they exist, but few can wrap their heads around what the physical reaction of the barrel steel is when the harmonics play out for the duration of a shot.
The most adverse effect of barrel harmonics on "accuracy" is unpredicatable movement at the muzzle. This movement comes and goes at the muzzle due to a shock wave that travels back and forth from breech to muzzle several times during the barrel time of the bullet. When the shock wave is nearing the muzzle, present at the muzzle, and just beginning to move away from the muzzle, we see the most movement of the muzzle itself...evident in the scattered groups we see, which by most users of OCW are called "scatter nodes".
OCW addresses that problem by systematically seperating scatter nodes from "accuracy nodes" by adjusting barrel time in very small increments with small incremental changes in powder charge. With this method of working through slowly increasing levels of pressure, and thus bullet speed within the barrel, and thus the time the bullet spends in the barrel, we can see by the groups we fire exactly what the harmonics are doing.
Over the years harmonics have been addressed with heavy barrels, rubber ring things, and that abortion called a BOSS system. Even bedding and floating has some effect on how the harmonics work. All these things do is either reduce the movement of the muzzle, or change the dynamics at the muzzle by applying an adjustable counter measure. OCW is a better way to address harmonics without the gimmics. I'm a believer in heavy barrels too, don't get me wrong, but a pencil thin barrel will shoot, with heat not being the issue, just as well as a heavy barrel if a load is worked up via OCW. In fact, thinner barrels stand the greatest chance for improvement with OCW loads because the thinner barrel's muzzle will occilate more than a heavy barrel's muzzle will. Simple physics there.
With OCW load development we are finding an optimum point in time for the bullet to exit from the muzzle, which is when the muzzle is at a calmer state, less movement, when the shock wave is not present at the muzzle. It's my experience that there are two useful windows of opportunity in any work up. One is about two thirds the way up the load parameters, and the other is just below a safe maximum pressure for the chambering.
The way we judge an "accuracy node" from anything else in the testing is by seeing a range of consecutive powder charges all hit the same point of impact in relation to the same point of aim. "Scatter nodes" will be anything that steps outside of those consecutive ranges and doesn't follow that same relationship between aim point and hit on target.
The width of the range of consecutive powder charges in an "accuracy node" is relative to the size of the case capacity, and thus a smaller case capacity will have a narrower window of accuracy for a good node, and a larger case capacity will have a wider window. It makes sense that smaller chamberings should increase test charges in .1 grain increments; medium size chamberings should increase charges by .2 grains; and large/magnum stuff can tolerate .3 grains of incremental increase. If you follow that system homing in on a load will happened much quicker for you.
When we find that range of powder charges that we deem the OCW, we typically take the middle of that range as our load. If group size is not exactly what we want we can further adjust barrel time by making changes to seating depth. Doing this either shortens the barrel time by making the distance the bullet travels shorter; or lengthens the barrel time by making the distance it travels longer. It's my experience that very small changes in seating depth, IOW .001" or .002", will make the most difference to a true OCW load making tighter groups. I believe this relates entirely to that amount of change to the barrel time itself, .005" or .010" is just too much and will put you out of the window you just found with changes in powder charge.
Some folks will argue that seating depth adjustment changes the amount of pressure on the bullet by increasing or decreasing internal case capacity. This it does do but if the changes are small as said above then the result will have a greater effect on barrel time than it will have on pressure.
If you apply logic to this then the entire range of pressures we found with charge weight (which IME is usually a full grain of powder in something like a 30-06) covers much more pressure difference than any small change in seating depth can ever provide. This is precisely why a good OCW load has an <span style="font-style: italic">inherent tolerance</span> for such things as slight variations in powder charge that are within the OCW range, changes in powder lot, different lots of primers, variations in case capacity within the same lot of brass, variations in ambient temperatures, variations in altitude, etc. It's not a fail safe for those condition changes but it certainly does reduce the effect they can have, and sometimes by a huge amount.
Testing OCW initially at 100 yards offers the best compromise between shooting conditions, ability of your gear, and human error. Initially we are NOT specifically looking at group size, but rather where on the target we are impacting, and we are looking for a range of powder weights that impact at the same point. Factor in anything that compromises our ability to precisely place those shots, since the hits themselves are our main measurement for the difference between "scatter" and "accuracy", and the testing can become skewed. An OCW that's found at 100 yards, will perform at greater distance also...providing we've done our job by matching bullet with twist, and providing we can actually shoot well at that greater distance.
This rifle here....
A recent build with the metal work by Old Lodge Armory. 14.5 pound Rem 700 with a 9.5" twisted 25" Krieger, chambered in 30-06. Took less than 50 rounds total to find the OCW with unsorted bulk WW brass, H4350, CCI 250's, and 190 SMK's. Initial testing at 100 yards showed 1/4 MOA right out of the gate in the accuracy nodes. Luck of the draw there, and no seating depth changes were tried.
Here's what it does at 500.....1.280" three shot group.
Again, yeah, OCW works, but it ain't magic.....YOU gotta do your part too, and it only works as it's been written by Dan. It's also gotta be understood that OCW was never intended to be the best thing since sliced bread. It was born out of the curiosity of why the hell does FGMM work so well in so many different rifles. It's not the bench rester's answer to all prayers. Dan explained this to me over lunch a while back. OCW is for the practical rifleman. It will give you a load that will substantially increase your accuracy predictability across a wide spectrum of variations over a long period of time. It's a god send for the guy who shoots all year long and doesn't want to dick around with impact shifts. It works for the guy who can live just fine with MOA or maybe a little better. It's the answer to making average factory rifles shoot more like customs. That's the bare minimum of the intent behind it, where you are able to take it is entirely up to you.
