i have been handlaoding for 12+years and continously search for the one hole group...cloverleafs accepted, but the one hole is prefered. tried the ladder process with mixed results. for years i would pick a bullet depth in the neck, pick a powder and load and shoot, increase load gradually and shoot and, continue until i occasionally found a great load but burned a lot of powder and barrels doing so. a recent event reinforces the merits of chris long's "shock wave theory and optimum barrel time" in reference to obtaining the one hole or very small group. his premise is that bullet seating depth controls the arrival time of the bullet at the muzzel and this can be controlled such that this arrival is when the barrel's shock wave is at the breech and the muzzel is at it's quietest which disturbes the bullet's departure the least, resulting in poi being the same or very close. this observation is not new as the "oldtimers" were aware that the barrel was doing a lot of things that affected accuracy. chris explains it in terms that are rooted in the science of this pastime. 5 thou difference in seating depth moves the group and at some point brings the holes to overlap. finding this depth is the challenge. i have a rifle and a one hole group with the bullet jumping .025 thou. just curious, so i loaded it with over .100 thou jump and found a one hole group jumping .127 in. there must be MANY of these accuracy nodes as the shock wave cycles from the breech to muzzel and back as many as 6-8 times before the bullet exits. i now get very accurate loads quickly. sometimes powder choice change is necessary to make all the components happy. just my observations.
finding an "accuracy node".
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I've been using the OCW and OBT method for a few years now. It's amazing how quickly a node can be found and then fine tuned with the seating depth of the bullet. The good thing is you're not continually chasing the lands and having to adjust powder to stay in the node. Once if's found and tweaked, it stays there. I concur, Sir!
John
John
Interesting, EXCEPT....
To what degree can you predict the harmonics of a barrel since there are great variances of steel composition and contour which all combine to define vibratory effect. Undoubtedly there are other variables due to rifling type and groove and land depths, plus bullet jacket thickness and Brinell Hardness of jacket material.
Lots of variables that effect and affect the harmonics. Would like to see some discussion of how you predict the moment of coincidence... That is what you're saying isn't it? That bullet exit from barrel be timed to troth or peak of the vibratory wave?
To what degree can you predict the harmonics of a barrel since there are great variances of steel composition and contour which all combine to define vibratory effect. Undoubtedly there are other variables due to rifling type and groove and land depths, plus bullet jacket thickness and Brinell Hardness of jacket material.
Lots of variables that effect and affect the harmonics. Would like to see some discussion of how you predict the moment of coincidence... That is what you're saying isn't it? That bullet exit from barrel be timed to troth or peak of the vibratory wave?
hogan said:
I don't think discussing how one might predict what you suggest would lead anywhere, given any one - or more - of the significant variables you mentioned in the first part of your post. Putting a value on all the variables would be tricky enough, let alone figuring out how any one affects all the others.
Actually loading up, then test-firing some rounds in a given rifle will make a better start.
It's really not at all hard to do: first load for a velocity (bullet weight + charge weight) that produces a small group down range (how small and how far is up to you) then change seating depth in small increments up or down to learn what effect each change has on group size.
Change something else on the rifle?
Start over.
Right. A barrel "rings" like a bell after a chambered round has been fired.
The ringing is energy being converted to vibrations in three dimensions, or four if you ascribe time as the fourth.
When you've "tuned" the load just fired to the rifle, such that the bullet fired leaves the barrel while all the various motions are at as close to the same point in the pattern of vibration for that load in that barrel, your accuracy will be maximized... assuming you've managed to keep that barrel pointing at exactly the same direction, and your target stays put.
I have a friend shooting a cartridge very much similar to one I particularly like. He's found that using the same propellant and bullet he gets accuracy virtually
the same as I've seen at similar velocities though his equipment and shooting style is different than mine. Coincidence? Partly.
The ringing is energy being converted to vibrations in three dimensions, or four if you ascribe time as the fourth.
When you've "tuned" the load just fired to the rifle, such that the bullet fired leaves the barrel while all the various motions are at as close to the same point in the pattern of vibration for that load in that barrel, your accuracy will be maximized... assuming you've managed to keep that barrel pointing at exactly the same direction, and your target stays put.
I have a friend shooting a cartridge very much similar to one I particularly like. He's found that using the same propellant and bullet he gets accuracy virtually
the same as I've seen at similar velocities though his equipment and shooting style is different than mine. Coincidence? Partly.
OCW method has saved me huge amounts of time & components in load development. It's interesting to watch what happens to velocity as a really solid node is reached, often it falls slightly with an increase of powder charge! I'm just now starting to explore the bullet seating aspect. One really needs to read both Chris Long's paper on shock wave theory and Dan Newberry's instructions for OCW method to get the best understanding & results.
execellant papers. i reread both often and learn or realize something each time. i have used the bullet seating concept on factory rifles and usually find a "node" that suprises me as to accuracy...talking about groups in the 2's occ in the 1's! i agree that jamming will often produce one hole, but some guns prefer a bit of jump. an observation: many of the guns in different calibers with different weight bullets seem to "node up" between .015-.030 thou off the lands. i'll load groups of three or five .005 apart and start shooting the deepest ones first. if i find the node early then the rest can be reseated to that length and save wear and tear on the barrel. unfortunately, i have noted that a good load and depth in the winter will often not shoot as well in the summer. seat this load .005-.010 deeper and SHAZAMM...the small group reappears, sometimes. othertimes, a change in powder gets the group back. it's obvious that seating depth is part( a very large part) of the process of obtaining accuraqcy.
hogan said:
This is my first post here.
I have believed that QL does not take in to consideration all possible variables in it's harmonic predictions but it provides an great place to start load development.
Recently, I have been experimenting with different configurations of muzzle brakes, some Swiss cheese types and some that are mostly air baffles. During these experiments I have questioned whether or not the length of the muzzle brake should be added to the barrel length, in my QL calculations, since the mass of the brake is dramatically different from the rest of the barrel and is changing the harmonic of the barrel.
Am I picking at nits of should I add the length, of the brake, and tweak from there
When my palma gun is shooting good on a day, you can hear it. The rifle has a certain "boing" to it.
Nomad - Thx, if Chris Long says no, then it is gospel!
one thing chris long doesn't talk about is...what happens to the air in the barrel after the bullet starts down it? saw a ?shadowgram of a muzzel showing the barrel air exiting as a transsonic wave ahead of the bullet, obviously. the molecules of air must precede the bullet and at 2.5 to 3.5+ the speed of sound. this wave slows very abruptly as the bullet penetrates it at 2.5 to 3.5+ the speed of sound. this could possibly explain the "going to sleep" behavior of the bullet that a lot of benchrest shooter refer to, especially with boattail ones. imagine the stress on the bullet as it tries to get going and it has to go thru a hurricane. add to this stress a supressor or a muzzel brake! that air wave is distorted in so many ways as it goes down the can or brake and the bullet still gets thru with a little disturbence, esp with the supressor. another reason why the crown MUST be perfect...a very small defect and the transonic gases behind the bullet push it off course and it goes thru the transsonic wave ahead of it crocked. how all this works simply amazes me.
http://optimalchargeweight.embarqspace.com/
http://practicalrifler.6.forumer.com/index.php
http://www.the-long-family.com/OBT_paper.htm
These three will get you started!
http://practicalrifler.6.forumer.com/index.php
http://www.the-long-family.com/OBT_paper.htm
These three will get you started!
the "boing" refered to is real. i have heard it but didn't understand what it represents other than the groups are usually great. another observation: could this "boing" represent a complete and total powder sublimation without much of the secondary burn or pressure spike that is talked about. i've seen somewhere on this site this mention of a secondary pressure spike, sometimwes extremely high, like 70,000 to ?90,000psi? the discussion goes something like...powder "ignites", pressure starts to rise and bullet starts to move, pressure goes down as the case volume goes down, bullet impacts the lands and pressure GOES UP! and bullet goes down the barrel as the pressure curve peaks and goes to zero after bullet exits. it has been observed that a case with very little powder(too little) can "detonate" this would follow the above sequence of events. near completely filled cases with the correct powder seem to work well. i thought a few times that my bolt lift became easier as the powder charge INCREASED! maybe that was real and ould be explained by no secondary pressure spike, but a complete and instaneous powder burn. it amazes me how many complex things can happen in such a short(1.3-1.8 msec) time.
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