Yes, a ladder test. Shoot a range of loads with their corresponding differences in muzzle velocity. Typically the hotter, faster loads print higher on target. Shift weight/stiffness around on the rifle until they shoot to the same elevation, at least over a part of the range.
Yes, a ladder test. Shoot a range of loads with their corresponding differences in muzzle velocity. Typically the hotter, faster loads print higher on target. Shift weight/stiffness around on the rifle until they shoot to the same elevation, at least over a part of the range.
Joe Woosman
Member
I have seen what Francis described many times. I recently did some extensive ladder testing with a long barrel 300WSM. There were distinct loads where the vertical was nearly gone but would then produce horizontal strings like Jackie referred to earlier. The loads where the vertical came together were at different elevations on the target and did not correlate with velocity.
Joe Woosman
Member
Also of note, I was shooting 215 Bergers with a BC of .696 from 2700 to 2900 at 100 yards with up to 30fps spreads. Comparing this to your above example of .040 at 100 I would say I am not seeing any effects of positive compensation but some sort of wave is moving the groups up and down with velocity. I just don't see how we can measure or confirm the effects of positive compenstion while the above is happening.
Francis and Joe,
Because of the complexity of muzzle motion, I don't believe that it is possible for a barrel to behave the same over a broad range of loads. That is why I said "at least over part of the range." What I am talking about is the general trend of the results over a wide range. Below is what I think is a typical result. Even though there are "stair steps" where the elevation is close to the same for a few charges, the general trend is upward with greater charge weight. Over two of the stair steps, there is nearly perfect compensation for a 0.4 grain range at this yardage (100). If this isn't typical of your results, then I would be interested to see yours.
After modification, the same rifle produced the results below at the same yardage. The downward trend (of the linear fit) is within about 10% of being perfectly compensated for 200 yards. There are three windows of 0.4 grains where the black average curve fits the downward trend fairly closely. Note that the modification completely changed the overall trajectory of the results. If we were to pick one, the modified rifle is better tuned, because of the greater vertical dispersion of uncompensated shots at longer yardage. But it would be better to have perfect compensation at both yardages, for which we need a different tune at each yardage.
Cheers,
Keith
Because of the complexity of muzzle motion, I don't believe that it is possible for a barrel to behave the same over a broad range of loads. That is why I said "at least over part of the range." What I am talking about is the general trend of the results over a wide range. Below is what I think is a typical result. Even though there are "stair steps" where the elevation is close to the same for a few charges, the general trend is upward with greater charge weight. Over two of the stair steps, there is nearly perfect compensation for a 0.4 grain range at this yardage (100). If this isn't typical of your results, then I would be interested to see yours.
After modification, the same rifle produced the results below at the same yardage. The downward trend (of the linear fit) is within about 10% of being perfectly compensated for 200 yards. There are three windows of 0.4 grains where the black average curve fits the downward trend fairly closely. Note that the modification completely changed the overall trajectory of the results. If we were to pick one, the modified rifle is better tuned, because of the greater vertical dispersion of uncompensated shots at longer yardage. But it would be better to have perfect compensation at both yardages, for which we need a different tune at each yardage.
Cheers,
Keith
Joe,
You have roughly double the BC, so the dispersion will be less without compensation. But all else being controlled, and with a stopped muzzle, faster bullets must track higher monotonically. That you are seeing waves with increasing MV is evidence of varied compensation. If you are finding stair steps where the elevation is constant over some range of MV, then you have found perfect compensation at that yardage.
Cheers,
Keith
JerrySharrett
Senile Member
One more comment for shooters new to tuners. Don't know if this applies to light weight tuners but it does to the heavy ones. If you are taking a known, good, fixed load like 29.2 V133 you will find that a given barrel will have multiple sweet spots. You just have to pick one you think is good enough since you could shoot a barrel out trying to decide.
Rimfire shooters use heavy tuners and will tell you they find multiple sweet spots, but, a rimfire barrel is good for a few to several thousand rounds where most centerfire barrels are gone in a few hundred rounds.
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Rimfire shooters use heavy tuners and will tell you they find multiple sweet spots, but, a rimfire barrel is good for a few to several thousand rounds where most centerfire barrels are gone in a few hundred rounds.
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adamsgt
Jerry Adams
Well, I might as well quit then. It takes me that many rounds to find a bullet and load that works reasonably well.
Oh well.
Dusty Stevens
Hollow Point Dispenser
Like jerry said find a known good load and tweak it. If it dont shoot get a new barrel. Shoot a normal load or get beat by one
mwezell
Mike Ezell
Dusty, I don't see where he said exactly that, but it's especially true with tuners. A known good load can virtually always be tuned to shoot with just a tweak of the tuner.
This is from experience. I'm not pulling anything from my backside. If I can use a tuner, anyone can. They really are as easy to use as I say.
This is a great thread, but we tend to get into the why's and how's, forgetting that it's a lot easier to do than to explain why and how. Someday all of that'll will be figured out. Til then, I'm gonna shoot with one, because it's much easier than tuning with powder charge and seating depth. It may sound too good to be true..but it's true.
All that matters is that there ARE easily found spots on the tuner where the gun will shoot..and that within a very small range of motion, the gun can be kept shooting through condition changes that would otherwise dictate a load change to maintain tune.--M
Joe Woosman
Member
Keith,
I think I understand you at this point. If there is stable, repeatable vertical impact over a range of MV that is less dispersed than the mathematical value predicted due to drag, there must be a positive compensation happening. I can buy that.
In my ladder test I was talking about, the lowest vertical value loads, (approximately .2), repeated about every 1-1/2 grains shooting in .5 grain increments. The .5 grain loads just prior showed the greatest uniform vertical string, (approximately .5). I don't believe even zero velocity spread could improve the group here. Since there is a clear vertical pattern happening, and that which is much greater than velocity spread can account for, there must be something much more critical to the relationship between bullet exit timing and barrel wave pattern. It does seem to me that if the muzzle were in the same exact position each shot the groups could be very small even with no vertical compensation. (I'm not promoting the "stopped muzzle" theory either).
Dusty Stevens
Hollow Point Dispenser
Post 88- that is what he meant by starting with a known good load. Some people will try to work up a load of some other powder with wolf primers in sako cases with a bullet made by somebody that makes 300/yr.
When you have a squirrelly load and then throw a tuner in there with a bad scope itll make you want to rub feces in your hair.
I ran your conditions through my calculator, and with a fixed muzzle, you would have the 2900 fps load striking 0.32" higher than the 2700 fps. So yes, you could have small groups at 100 without compensation. At 600 yards, though, no compensation would get you a 13" vertical spread.
0.32"/(2900-2700) = 0.0016"/fps. If over any interval you see a smaller rise, you have positive compensation.
JerrySharrett
Senile Member
That is exactly what I mean Dusty, thanks. Everyone who shoots the PPC, for example, a lot, like for years, pretty much have a standard starting place, i.e. a known good load.
Best example Tony Boyer. Mr Boyer, who has more than 3 times the HOF points of the next three on that list combine can, with his known good load, with confidence, test 15-20 barrels within 20 shots per barrel to see which he plans to keep for that season.
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mwezell
Mike Ezell
I couldn't agree more Dusty. But say your load typically changes, over the course of a match, from 29.2-30.0 gr. That's a range of charges that are good in your gun at varying conditions, temps, etc. Tuners make it possible to load any of those charges, assuming no pressure issues, and shoot that same single charge all match long, without changing powder charge/seating depth to maintain tune.
Simply load up 29.2 and maintain tune by just nudging the tuner..when or if needed. Or, you could do as Mr. Bukys, and still tune traditionally, but not see the sharp and sometimes frequent fall offs in tune that can happen, particularly with a ppc and 133. The benefit of a tuner here, is the wider tune window.
But as you said, a tuner will no more fix a gun problem than it will a bad bullet problem.-Mike
mwezell
Mike Ezell
I agree Tim! Very little or no bickering, but lots of good info from some very smart people. It's hard to discuss tuners and not have infighting. This one defies that for the most part and is mostly in terms that the majority of us can understand. That's hard to do, also. These threads about tuners can quickly get into terminology that causes people that don't understand it, to lose interest and fall back on arguments that they've heard as being gospel.
I have an interest in knowing all I can about how they work, but realistically, it's so easy to make them work, understanding the why's and how's is not nearly as important as some make it to be.
The biggest hurdle, IMHO, to using tuners in cf is weight limits in LV class. For that reason, and to make them more viable for the most popular class in cf(LV), to get more people to use and experiment with tuners, we either need lighter tuners or more tuner friendly barrel profiles...or both.
I do truly feel that if more shooters in that class started using them, it'd snowball fairly rapidly.
The biggest difference I see in cf vs. rf is that some feel like the stopped muzzle theory is workable. I don't, but that's what these discussions are good for. As I understand that theory, the bullet exit is timed with the vibrational node where that node is moved to the muzzle and the muzzle is "stopped". It's my understanding that this is physically impossible, as moving that node to the end of a cantilevered beam isn't possible.
Perhaps Keith or someone can elaborate on this.--Mike
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Boyd Allen
Active member
That whole stopped muzzle thing is a rimfire Calfeeism, and (IMO)does not comport with CF theory that is currently in use. To move a node to the muzzle, there has to be sufficient mass extending past it, and I do not believe that any of the tuners that are currently being use for CF work have that feature. What I think is happening in the CF world is that tuners are being used to modify the frequency of the barrels vibration during firing, so that the bullet will exit at the desired point in the cycling of muzzle motion. Beyond this, with some designs, there are attempts to damp spurious vibrations.
mwezell
Mike Ezell
Absolutely Glenn! It may or may not help with the physics behind them but I agree that we'd learn a lot if more people try them.
Dusty Stevens
Hollow Point Dispenser
Mike i know you use the science of particle dampening- have you tried other things? Different powders, mercury, glycerine, glycol, oil? I have an extensive background on balancing rotating machinery and those items mentioned are some of the things we use