Re: powder and accuracy
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ericf</div><div class="ubbcode-body">Ok, this is going to sound screwy, but if barrel harmonics is one of the variables for accuracy, Then why bed the action and float the barrel? Wouldnt floating the action and bedding the full length of the barrel help eliminate this negative?
Sorry for this assumption, but I'm just applying simple logic (which I know cant be done) but for the purpose of those that know.
Thanks,
Also, harmonics is a product of bullet and velocity through the barrel. With the bullet and velocity being equal, the harmonics should be the same. Acceleration does play a role, but it couldnt?? play that large of a role given a shorter length barrel and an equal velicity. (could it?) </div></div>
Bedding an action is to provide the action with a solid foundation so it's movement and flex are as limited as possible.
Floating the barrel allows the harmonics to behave as close to the same way, consistently, from shot to shot, without an increasing influence from contact with the stock and the effects of barrel heat.
Full length bedding the barrel only works on some rifles, and barrel harmonics are the deal maker/breaker if it works or not.
I've heard of floating a .22RF action and bedding the barrel, but I would never consider it practical with a high intensity centerfire. The recoil lug on bolt rifles is what saves the system from self distruction, and that's quite well connected to the action, which must be in contact with the stock for it to work...thus bedding the action for a solid foundation.
Barrel harmonics are going to be there no matter what you do......
Negative effects of barrel harmonics come into play at the muzzle, when the shockwave is at the muzzle causing the muzzle to move and oscillate, which throws the bullet to an unpredictable POI; the trick is to time the exit of the bullet when the shockwave is not affecting the muzzle in that way. Translated, that produces an "accuracy node", or good groups. When the muzzle oscillates from influence by the shockwave, that produces a "scatter node", or bad groups and flyers.
I typically see two accuracy nodes in the parameters of load development that I concentrate on. In between those accuracy nodes I also see the width of the scatter nodes. What that means is that the shockwave travels from the breech to the muzzle, and back, at least twice while the bullet is accelerating inside the bore. What that means is the shockwave is a whole lot damn faster than the bullet. What that means is my human perception of whatever physics is taking place from ignition to bullet exit can only be defined by knowing I shot the round and feeling the recoil. What that means is I have no way of comprehending or measuring the dynamics of what is taking place inside that cartridge case and/or bore with the difference between two loads 1/2 grain of powder different, or the difference between one brand of powder or another. What that means is, because we are on the super micro scale of time and action, it's not too difficult to realize all it would take is a very small change in internal ballistics to make a big difference in the dynamics of what's going on.
Different powders, despite having similar burn rates, are by the very essence of definition, different. To achieve the exact same internal ballistics to produce the exact same shockwave, to produce the exact same results, would mean they couldn't possibly be different. H/X brand of powder produces one set of internal ballistics because of it's nature determined by it's properties; IMR/X brand of powder, although very close in burn rate to H/X brand, is made by someone else of different compounds, and will produce it's own set of internal ballistics determined by it's own properties.
Everything you are questioning is what is taking place as; the powder ignites and begins to burn in a controlled explosion, as the brass expands in all directions, as the chamber walls expand, as the bullet begins to move, as the bullet enters into the lands, as the bullet leaves the case neck, as the brass is forced rearward, as the bolt lugs slam into the lug recesses, as the bullet begins to travel down the barrel, as the building pressure expands the barrel behind the bullet, as the bullet accelerates to it's fastest possible speed governed by the pressure behind it over the length of the barrel, as the bullet exits the muzzle....all while a shockwave, produced by the initial "explosion" of the propellent, is slinging back and forth over the length of the barrel and chamber causing the muzzle to oscillate, calm, oscillate, calm, oscillate, etc.
Change just one of those events by even the slightest amount in time or action and you've changed all the rest of the components of the equation....thus the "difference" between two powders despite all things being generically "equal" by our human perception of it. Some differences are not so bad, and are within an acceptable range of tolerance, some just aren't.
