Sweetspots, harmonics, chronographing.

26 October 2002, 09:50

trans-pond

Two primer/powder combinations. Both using same bullet, same brass.
If I get one grouping really well, can I chronograph it and get the other load to shoot equally well if I mirror the velocity?
i.e. is sweetspot /harmonics purely about velocity? Or am I being really dense?

26 October 2002, 13:50

Ku-dude

I would say that barrel harmonics are not directly tied to velocity of a bullet. The harmonic is more like stiking the barrel with a large hammer, and having it vibrate. It is the striking that sets up the harmonic, and as you know powder charges result in different velocities. The charge that produces the same velocity would have a different "bang" or "twang." This is why several powders may give you good accuracy at different velocities for each. I hope this addresses your question. Ku-dude

[ 10-27-2002, 23:11: Message edited by: Ku-dude ]

26 October 2002, 13:58

boltman

In my experience matching the velocity seldom achieves the same accuracy. I think there are other things involved with getting to the "sweet spot" than just velocity. Things like pressure rise time, powder weights, etc. also factor in.

26 October 2002, 17:15

DB Bill

The reloading program has a feature called "barrel time" and this is about the closest thing you will get to matching the harmonics. Input various info and it will show you barrel time or you can do it in reverse. Not perfect but close as I used it to get 300gr softs and solids shooting to the same point of impact in my .375........300gr Noslers at 2550 fps and the 300gr solids at 2475 fps.

27 October 2002, 01:36

Hot Core

quote:
Originally posted by trans-pond:
... is sweetspot /harmonics purely about velocity? ...

Hey trans-pond. No, it is much more complex. No need to give yourself a hard time about not completely understanding the way it works.

Every portion of the Firing Sequence has an effect on the bullet exiting the barrel at a "similar harmonic" to the other shots within a group or series of groups. Not only the specific components within the actual "Load", but even variable things such as the changing bore condition, consistent grip on the firearm from shot to shot, etc., can change the harmonic position when the bullet exits the muzzle.

As a person does begin to understand the complexity of this issue, shooting a small "bragger" group is all the more amazing. Lots of things working against it ever happening, but occasionally we all get a Load that shoots pretty good - AMAZING!

Use the Creighton Audette Method of developing your Loads, it has never been improved on by anyone. Shoot at 300yds if at all possible and you will be able to see the results of the bullet exiting at different points along the harmonic fairly easily. Look for shot clusters which indicate those Loads exited close to the same harmonic peak. Then fine tune the harmonic by adjusting the Seating Depth and you will get the best possible accuracy from those specific components.

...

Now, with all that said, there is still a slight chance you could possibly regulate the "velocity" with a totally different Load (comprised using different cases, primers, powder and/or bullets) and have those bullets exit on a similar harmonic. But, the odds are stacked highly against it.

[ 10-26-2002, 17:40: Message edited by: Hot Core ]

27 October 2002, 01:57

TCLouis

From my experience reloading is a perfect example of what a friend of mine that is one of a group of college professors has as a motto . . .'when it comes to high temperatures and pressures, it ought to, should not come out of your mouth.' Do an experiment to see the results and then go from there. And yes, they are ALL "eggheads" that do practical things, not just "academics" who are intelligent, but don't have sense enough to pour piss out of their boots [Big Grin]

(as the saying goes).

And that is just what reloading seems to be, a series of experiments to find the one . . . or none . . . load that works the the chosen powder or bullet or powder/bullet combo!

Of course to me, that is what makes it fun!

LouisB

Just a bunch of opinions strung together of course! [Razz]