Seating Depth Work up Q
- Thread starter daveyboy
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Andrew Leigh
Member
Like I said google Chris Long's OBT Theory. He explains it all and he has a free download of the node calculator. The only problem is that it is pretty useless without Quick Load but the thery is good.
Reloadron
Contributing Member
I think that theory is flawed because it's based on assumptions.
Real data disproves it handily. For example, people shooting 7.62 NATO Garands saw no accuracy degradation as the bore and groove diameters enlarged .002" from bare steel cleaning rods rubbing away metal at the muzzle. There was copper wash all the way to the crown when new. After 3000 rounds, accuracy was still the same but the copper wash stopped near 3/4" back from the muzzle. Muzzle wear gauges showed a .002" increase in bore and groove diameters. Ten times as much as Chris Long's numbers for muzzle enlargement from shock waves.
Too many people have shot the same load in different barrel lengths with the same good accuracy in each.
I think that OBT stuff is one of the myths that most people cannot see the flaws in. One is a rifle barrel's resonant frequency is typically less than 100 Hz. So says mechanical engineers using the fourth order equations getting good answers. Check out www.varmintal.com the Barrel Harmonic Movie. And his speed of sound in barrel steel is incorrect. Plus, sound waves don't stop at the receiver; they go back to its tang then bounce forward.
Real data disproves it handily. For example, people shooting 7.62 NATO Garands saw no accuracy degradation as the bore and groove diameters enlarged .002" from bare steel cleaning rods rubbing away metal at the muzzle. There was copper wash all the way to the crown when new. After 3000 rounds, accuracy was still the same but the copper wash stopped near 3/4" back from the muzzle. Muzzle wear gauges showed a .002" increase in bore and groove diameters. Ten times as much as Chris Long's numbers for muzzle enlargement from shock waves.
Too many people have shot the same load in different barrel lengths with the same good accuracy in each.
I think that OBT stuff is one of the myths that most people cannot see the flaws in. One is a rifle barrel's resonant frequency is typically less than 100 Hz. So says mechanical engineers using the fourth order equations getting good answers. Check out www.varmintal.com the Barrel Harmonic Movie. And his speed of sound in barrel steel is incorrect. Plus, sound waves don't stop at the receiver; they go back to its tang then bounce forward.
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Andrew Leigh
Member
The one nice thing about advice is that you can always ignore it, and or take the bits that apply to your theory.
OBT does work, whether you like it or not, I can put good hand loaders on an accurate node within 12 shots. Using OBT and QL. Have done it over 60 times without fail with numerous calibres.
The resonant frequency is a function of barrel length hence the Optimal Barrel Time. OBT says nothing about the speed of sound.
Sound waves do stop at the receiver and end at the muzzle. there is insufficient mechanical coupling through the threads to provide a mechanical extension to the barrel either through the receiver or through a sound moderator.
I am not forcing any theory on you and will not argue it either.
I've put an accurate load in all sorts of barrels with one shot. Never worked up any load for different barrel lengths for the same cartridge. Nobody's got better accuracy.
Nobody's proved that OBT theory is correct measuring bullet exit versus pressure pulse position.
As bullets with a wide range of weights and muzzle velocities won't have the same muzzle velocities and barrel times for a given load in the same rifle shot by different people. There's easily a 100 fps spread for average fps numbers. Yet the same load shoots equally accurate across several people. If Long's OBT really worked as claimed, a different load would be needed for each of several people shooting the same rifle.
That shock wave travels at the speed of sound in steel. It's amplitude is greater.
Nobody's proved that OBT theory is correct measuring bullet exit versus pressure pulse position.
As bullets with a wide range of weights and muzzle velocities won't have the same muzzle velocities and barrel times for a given load in the same rifle shot by different people. There's easily a 100 fps spread for average fps numbers. Yet the same load shoots equally accurate across several people. If Long's OBT really worked as claimed, a different load would be needed for each of several people shooting the same rifle.
That shock wave travels at the speed of sound in steel. It's amplitude is greater.
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Andrew Leigh
Member
I don't quiet know how to answer that but clearly you don't need forum help on developing loads.
Clearly you have not taken the time out to read the links provided. Thousands of rounds were used to assimilate the data while using electronic measuring equipment on the muzzle to measure the deformation. OBT is merely a mathematical explanation of the OCW method.
There are multiple Nodes for any given barrel, this allows one to tweak for the speed and bullet weight combination desired.
You really should read the philosophy before declaring it invalid.
For magazine fed guns, make sure the loaded round fits in, and feeds from, the magazine and keep the bullet off the rifling when chambered.
For revolvers, make sure the round chambers easily and doesn't extend beyond the cylinder face.
My 45 years of loading has taught me that in most cases the exact COAL is not all that critical so long as you assure proper chambering of the round. In some cases (max loads, super high accuracy and etc.) you may need to do more tweaking.
For me, bullet profile, nose shape, diameter, powder, primer and such are far more important to practical accuracy than an exact COAL that always places the bullet x-thousands of an inch from the rifling.
For revolvers, make sure the round chambers easily and doesn't extend beyond the cylinder face.
My 45 years of loading has taught me that in most cases the exact COAL is not all that critical so long as you assure proper chambering of the round. In some cases (max loads, super high accuracy and etc.) you may need to do more tweaking.
For me, bullet profile, nose shape, diameter, powder, primer and such are far more important to practical accuracy than an exact COAL that always places the bullet x-thousands of an inch from the rifling.
spitballer
Member
Thank you A. Leigh. Nodes and resonant frequencies mean little to guys like me who have a hard enough time simply maintaining consistency from one round to the next. 1/10th moa from resonant frequency modulation is not going to trump 3/4 moa spread from varying neck tension when I'm seated into the lands. For guys like me who simply trying to maintain a decent consistency the best strategy seems to be eliminating or at least moderating the variables that introduce that inconsistency. Finding a propellant/primer combination that starts with enough pressure for the bullet to deform properly and then adjusting the charge just enough to eliminate muzzle upset is something I can understand. I've been accused of "overthinking" but WOW now I'm losing sleep over resonant frequencies
Andrew Leigh
Member
People have been reloading for years using the barest minimum of data and have achieved acceptable results and have put food on the table. Many have managed to get good load recipes but do not understand why, for most this is also OK as long as the result is there many will not question.
As in any sport technology comes along cleverly disguised as a marketing tool, in order to sort out the chaff from the wheat one is almost forced to delve deeper simply to understand what the new product offerings are giving over and above the old product offering. Some of us find it exceedingly difficult to blindly accept marketing blurb without testing the information.
Then there are those who delight in the technology and who like reading volume after volume while trying to further understand what is behind concepts like pressure, trajectory, twist, bullet mass and how these all fit together. I am afraid that I unashamedly fall into this category. I like the technology as it gives me joy to learn more. This I have practiced my entire adult life and so every hobby I approach it is with this same application to the task.
Neither approach is incorrect I simply prefer the latter.
Horses for courses.
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