Ladder test with only a Chronograph

B

BJung

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How do you guys fine tune your test loads?

I've started loading my rifle test loads .5 grains apart and later comparing my prints and the mv to find the Nodes. I'd take the two loads that printed the closest and take the average.

Does anyone repeat the ladder test at .3 grains apart within that Node Window or would you make a test loads (of say 4-5) and choose the load with the best group?

The use of the ladder test is well documented but still new to me in actual experience. Have most of you just used the ladder test, found your Node, and moved on having your pet load in hand? What about handguns? Have you done the same. And if so, you wouldn't need a target.

In theory, with a lack of time, I could just go to a range, shoot my test loads without having to wait and setup targets during a ceasefire through my chronograph, and leave with my MV results that indicate the Node, yes? I like looking at my printed target but when this Pandemic lockdown is over, the range is going to be full and I won't have the luxury of hogging three targets for myself.
 
What range are you testing at?

What ranges will you shoot at after doing ladder tests?

I ask because ladder tested loads are best for only one range
 
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Bart,

I think he's using the velocity flat-spot ladder and not a POI ladder. Dave Milosovich, writing in the Precision Shooting Reloading Guide for 1995 showed a plot in which several spots could be identified where increasing charge did not have a corresponding increase in velocity. He considered it a reasonable starting point for load tuning that identified candidate loads. But unless you get a velocity flat spot that is also synchronized with your muzzle deflection timing, you still won't have the tightest groups the gun could get. This is why barrel tuners help, no matter how low your velocity spread. The same-velocity shots don't necessarily have the exact same barrel time, as the lightest charge producing a given velocity will have a shorter barrel time than the heaviest charge that produces the same velocity. The velocity flat spot would be all you needed if the gun were perfectly rigid, but that's not what we have in a rifle you can carry. So you really need both kinds of ladders to fully optimize load tuning. Unfortunately, as Randolf Constantine pointed out, the Auddette ladder is easiest to read when fired at about 300 yards, which a lot of folks don't have available. I think Creighton Audette used just 200 yards, but he would have been using benchrest competition guns for which resolving very small vertical displacement was easy to do.


Burbank jung,

I think Dan Newberry's OCW method is right in suggesting load steps should be in increments of between 0.7% and 1% of your charge weight. This means the number of grains per step will differ with the size of the cartridge, and I don't know what cartridge you are loading for, so I can't answer you question about step size. 0.5 grains is fine in in 30-06 being loaded with 50-60 grains of powder. In a .223, a step that large could easily pass right over a flat spot.

If you want to work with the velocity ladders, I would shoot at least three identical sets of charges and plot them on a graph so they overlap to get some idea of how much normal velocity variation affects the apparent flat spot locations, particularly at the ends. Some such spots may turn out not to be real, instead being an illusion created by random velocity variation. If the variation makes a flat spot you are interested in uncertain, you'll want to fire a larger number of samples near the flat spot to see if you really found one. I think that is what you were intending to do with the smaller charge increments, but I would start with those to increase the resolution of the flat spot across the whole range. You can also average all three velocities at each charge to smooth the plot out some. You may even find you want more ladder results to average if it still isn't pretty apparent.

You'll benefit from handling each cartridge identically, as SAAMI recommends for testing ammunition. Point each one up and rotate it through a circle on a vertical plane to move the powder back over the primer (but don't tap it on anything as that can pack the powder and lower its effective burn rate), and then chamber it slowly and smoothly so as not to throw the powder forward. This will maximize pressure and velocity with the loads that don't fill the case well.
 
For this load I am not concerned about velocity nodes, everything to do with POI. Can be loaded plus or minus .1 grains and still have 9 out of ten shots land in a .4 MOA group. You can use this load with a old school throw, never weigh and still get a consistent POI. Same theory works for short range to mid range. I am sure velocity plays a role but target analysis will tell you all you need to know. Chronos are a rather new kid in the shooting world. Lots of good shooters developed a lot of good loads back when a chrono that told time.Don't get me wrong I chronoed and logged the tests but that is more for future reference than anything I will use to determine my load.

My advice to the OP is just go shoot some groups, go with the one that shoots. Chrono for curiosity and record keeping. Even at long range you can see what works by just shooting
 
I was composing while you posted. I should have put Bart's name in to direct the first part of my post. I hadn't seen your post at that point.

Velocity node ladders appear to be what the OP is asking about, based on the thread title.
 
My bad Nick

Guess I took a roundabout way of answering the OP. What I do is a rough test .5 gn's apart then when things start to come together I switch to .3 and look for a .3 gn flatspot for either POI convergence or velocity or both depending on what the load is meant for then load to the middle of that node. Clear as mud right?
 
still want to empahsize that in short and mid range POI means all. Chrony data is just for records and gives me a reliable pressure warning if my MV gets too fast. I have a .223 80 gn SMK load that has a ES of over 150 FPS, @ 300 it shoots .7 MOA 10 - 20 shot groups consistently
 
Unclenick,

Thanks for clarifying the velocity ladder methodology.

I've heard of incremental charge weights null point which is probably the same thing. Took a while to figure it out.
 
Hi Bart - I usually shoot at 100 yards because I think I'll be more prone to ruin the POI because of Shooter Error. My tests are prone to error because I can't see 100 yards anymore without optics, with a binocular and barely ( like maybe ) with my vintage spotting scope. I shoot, record my MV, walk to the target, count the holes ( yup, same number of holes! ) and assume the POI corresponds to the MV since I couldn't see where the holes were printing.

Uncle Nick - I'm lazy but admit, the more samples, the better. I use both methods I suppose but want to fall back with the chronograph if there is a lack of time. I'm not complaining about people taking too long to return to the firing line mind you, I'm in the berm with a shovel digging for lead or picking up brass. I collect and look at my targets later. Better than so-so centerfolds.

Thanks for the homework guys.
 
Bart - Ladder testing is only good for one range?? Do you mean I need to make a ladder test for 100 yards, 200 yards, and beyond? Please clarify.
 
burbank_jung said:
Bart - Ladder testing is only good for one range?? Do you mean I need to make a ladder test for 100 yards, 200 yards, and beyond? Please clarify.
Click to expand...
Probably not.

For point of impact (POI) ladders wherein the powder charge is adjusted such that their velocity spread makes the bullets leave on the muzzle axis upswing so slower ones leave at higher angles than faster ones so their trajectories cross at target range, that charge weight is good for only one range.

From both trajectorie's first cross point (a few yards down range)to target, slower bullet's trajectories will be above those of faster bullets. From their second trajectory cross point at the target to longer ranges, slower bullet's trajectories will be below those of faster bullets. Their trajectories to the target will be furthest apart at about 60% of target range.

At ranges less than 300 yards, POI ladder tests at 2/3rds of maximum range will cover all of them very well unless you shoot your stuff no worse than 3/4 MOA.
 
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hounddawg said:
Lots of good shooters developed a lot of good loads back when a chrono that told time.
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Chronographs measure speed rate over a distance.

Chronometers show exact time of day in standard units. Some have push button chronograph functions.

Often confused
 
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hounddawg said:
and which ones are referred to as chrono's? Hmmm both maybe
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Neither one very much. The chronograph functions are often built into chronometers as well as standard wrist watches then sometimes called and labeled tachymeters.
 
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Nodes and Barrel Vibration

I read Dan Newberry's writings as suggested by Uncle Nick.

If the most accurate load is one in which the vibration has travelled down tot he muzzle and returned to the receiver just as the bullet is leaving the muzzle, then the accuracy nodes are this vibration is at that point, yes?
 
It's looking for a deadspot in the change. Follow this link to Chris Long's Optimum Barrel Time Theory for one approach to looking at it. I think, though, that if there were nothing in harmonic barrel deflection, barrel tuners wouldn't work, but they do. Similarly, bullet seating depths that are better across a range of charge weights wouldn't work, either. So I think the reality is there is more than one tunable dynamic involved, which is why these different approaches all work to different degrees with different rifles. The ideal will get all the dynamic factors optimized at the same time.
 
The OBT theory states the barrel muzzle outside diameter enlarges a few millionths inch several times every time a round is fired. The bore diameter enlarges too, but I don't see how much is stated. And bullets leaving the muzzle when its diameter is enlarged are supposed to not shoot as accurate (precise?) when that happens.

OBT theory implies all barrels of a given length regardless of its profile dimensions, caliber, bullet weight and cartridge will shoot most accurate with the same barrel time intervals. The theory uses a hammer striking the barrel which produces a narrow spike shaped shock wave. Cartridges produce a wider rounded shock wave. Theory ignores the vertical bore axis whip that changes LOF angle to LOS across the velocity spreads that tuning weights near the muzzle change its frequency.

The resonant (lowest or fundamental) vibrating frequency barrels vibrate at several dozen cycles per second, not several thousand claimed in the OBT paper. The muzzle axis vibration frequency bullets leave at is several hundred CPS (or Hz, hertz), not several thousand as claimed.

While the paper says even 0.3 grains difference in a 25 grain .223 AI load was enough to take it from a 0.5 MOA group to a 1.2 MOA group, I think the bullets left across a smaller vertical LOF

Why did the several Garand barrels I wore out show no loss of accuracy as the bore diameter at the muzzle enlarged over a thousandth inch after a couple thousand or so rounds from bare steel cleaning rod wear? No copper wash the last half inch of the barrel and the muzzle erosion gauge reads near 2. Gauge read about 0 with a new barrel.
 
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Burbank_jung,

You might consider one of the target cameras that talk to your smartphone or tablet or laptop by Bluetooth. You set it down near the target and aimed at it and it sends the image to your device in real-time.

Regarding the different ranges, the main reason Randolf Constantine recommended 300 yards was to get adequate bullet drop difference between load increments. For example, a 30 cal 168-grain Sierra MatchKing fired from a perfectly rigid barrel at 2500 fps and again at 2550 fps will have a drop difference of e 0.11 moa at 100, 0.24 moa at 200, and 0.39 moa at 300. That means your ability to hold has to be that good to be sure you see the 50-fps velocity difference as a vertical separation on the target.


Bart

The OBT theory considers an analog to the same problem with harmonics: you get accuracy as long as the muzzle you shoot through is symmetrical and is in the same position or has the same shape at the moment of every bullet’s departure. But if you have the bullet exit during rapid transitions in any of those factors, small variations in barrel time can produce different POIs on the target.

But as far as the diameter change, it depends how thick the muzzle is, but it is not a lot. It would be proportional to multiplying the outside change by the outer circumference divided by the circumference at the groove diameter. I have also looked at the pressure waves on Pressure Trace plots and on some old piezo transducer plots, and they present as the equivalent to one or two thousand psi. I did hoop stress analysis for a thick wall cylinder on that equivalent pressure, and it agrees the diameter changes are on the order of a millionth of an inch.

One problem in attempting to arrive at a measurement of this is both the piezo transducer and strain gauge measuring systems have response speed limitations that reduce the apparent magnitude of the waves on the display. So, the pressure equivalent deformation is likely larger than appears on the readout. Nonetheless, I am, as I am sure you are, highly skeptical that millionths of an inch, even changing during bullet exit, would produce measurable dispersion on the target.

That said, the OBT and velocity flat spots you can map out with a chronograph do seem to have some correspondence. I think the more likely mechanism is suggested by some of Varmint Al’s analysis. I note the frequency of a pressure wave traveling up and down the barrel is about twice that of Al’s mode 6 harmonic vibration. It also has two lumps in it, so even if it were at Al’s mode 6 frequency, you would see two occurrences in each cycle. The barrel extending and retreating like that under the influence of the pressure wave would alternately add-to and subtract from bullet velocity via the friction between the bullet and the barrel surface. Another possible mechanism is the pressure wave attempting to straighten the barrel, thereby messing with the timing of muzzle swing. These are just ideas on my part and not known to be a fact, nor I have I identified an experiment to prove one or the other. My point is mainly just that other mechanisms than Chris’s muzzle distortion idea are possible. So his timing predictions could be right even if the mechanism he offers Is not.

One last thing to note is different steel alloys have a little difference in the speeds of sound in them. Stainless and chrome-moly won’t be the same. I think this is why Chris Long suggested the nodes predicted were within about 2% when measured. That’s right about what the sound speed range is going from stainless to mild steel.

I don’t know what to make of chronometer vs. chronograph. The first word is literally “time measurer” and was first used in 1676. The latter literally means “time writer” which distinguishes it from a chronometer by making a record of the time it measured, even if only a temporary record, as with a stopwatch. The term first appeared in 1851. However, the dictionary also describes chronometer and chronograph both as synonymous with timer. I’d always assumed a ballistic chronometer was a bullet stopwatch that gave you the bullet transit time between two points rather than a velocity reading, leaving you to work out velocity for yourself from the time difference. But it seems the dictionary leaves that a shaky difference, as chronograph can be applied to both.
 
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