Greg,
Thanks for the reply.
I don't shoot any games so holes in the tuner is a non-issue. I've also read extensively regarding the effectiveness of tuners but have never read about the effectiveness of a tuner/brake thus the inquiry. As a reloader, it is apparent that finding the load the gun likes and then dialing in the tuner is the path to wander down.
Anybody else?
Greg, very well said. You really got the idea across in what I think is a very understandable way... accurately.Ok. Some more on this.
A tuner will not make a bad barrel good. Nor the reverse.
It will not make a crappy load good nor the reverse.
Let me start by saying that the the barrel oscillates like a tuning fork when you shoot. For the sake of this discussion, let’s be simplistic and say that the barrel whips up and down to form the halves of a sine wave at the top and bottom.
Now, where the muzzle is pointing when the bullet leaves it is where that bullet is going.
That’s important because there are *always* small variations from average in when the bullet gets to the muzzle. At a given moment of shooting, those variations are small, but significant to some shooting formats.
Across a shooting day, as the temperature increases, the velocity will increase and change the average from which those small variations occurs.
That’s important because on one half of that sine wave, the oscillation aggravates the small variations, while on the other half, the oscillation actually helps compensate for the small variations. This is called “positive compensation”.
When a short range benchrest shooter changes powder charge to chase the tune during a shooting day, what he is doing is keeping the average on the correct side of the sine wave.
BTW, It is also why the shooters groups get tiny right before they blow up. :/.
You can see this by drawing a horizontal line across a 2’ wide target and vertical lines at even intervals on the line to form target crosshairs. Kinda like graph paper, if that helps. Then shoot two or three shot groups from left to right increasing powder charge in small increments, say 0.3 for small cartridges and 0.5 for big ones. You will see the group’s form a sine wave. Half above the horizontal and half below.
The “correct side” is the side where increasing powder charges move the groups *down* the page. The bad side is when the opposite happens.
What a tuner lets you do is stay on the correct side of the sine wave *without changing powder charge* (or seating depth, etc). It does this by tuning the barrel to the load rather than the normal method of tuning the load to the barrel.
There are other benefits to a tuner (and other downsides), but that is enough for now.
The way that I use a tuner is to find a load that works...that is in the middle of the “correct side” using the “graph paper” method that I described above, then use the tuner to stay there as the temperature increases during the match.
I think of it this way. It’s not what’s really happening, but it’s a way to remember. As the temperature increases, the velocity increases. I move the tuner toward the action, as though I were shortening the barrel to reduce the velocity.
I highly recommend that you get with “gunsandgunsmithing”’on here. That’s Mike Ezell. He has a metric buttload of tuner experience and manufactures a very nice tuner. He’ll explain this better than me and correct anything that I’ve gotten wrong.
That’s all I’ve got and my thumbs are about to fall off.
Greg J
Good explanation of "positive compensation" and what to look for, Greg. I agree about there being room for the right people to experiment with barrel contours in this regard as well. Putting a mass at the end of the barrel effectively does this, as do straight contour barrels.--MikeView attachment 1031001 After a PM or two, here is some more explanation.
Caveat: I do short range. Not long range. Can’t speak to long range.
Also, while I have experienced this directly, I didn’t come up with it. I got onto this from talking with several HoF short range benchrest shooters.
You can see this “good part” really clearly on the top/far right of the previous picture that I posted. Immediately before that, you can see the bad side. (Now, truth in advertising: As I said in a that post, I was actually moving my tuner to show the effect to a friend, not increasing powder charge).
Why the upswing? Because bullets that get to the muzzle late, generally moving slower, are put onto a higher trajectory. Bullets that get there early, generally moving faster, are put onto a lower trajectory.
It’s not obvious, but speed that the barrel is oscillating at the point that you tune around...the average exit point...only allows the compensation to be right at one distance.
I’m kind of reaching here, but I think there is opportunity there for experimentation with respect to barrel profiles to allow for better compensation. View attachment 1031001
GSPV:
I'm mulling over your chart. Some questions.
1) Is the y-axis depicting muzzle position relative to a static zero or the downrange point of impact of the bullet?
2) What is the x-axis denoting? Powder charge, bullet speed, or time?
3) What physical factors other than length do you believe influence barrel harmonics?
Thanks.
I don’t think that that is necessarily just in long range, either. Longer distance would seem to require more vertical movement of the barrel with respect to the variations in exit time.Adding muzzle weight slows this, as well as slows the vertical travel of the muzzle in its harmonic. So far in LR it looks like the faster we can get the muzzle going up, the better.
Those sine wave charts can be a little misleading, as the barrel is mostly going up and down not actual in a sine wave. .