Chronographs useless?

[mcb]

+/- 0.5% accuracy is IMHO pretty good for a lot of sensors in use out there and as an Engineer I have used a fair number of instruments for measuring a variety of things. For a chrono that you only paid a few hundred dollars at most +/-0.5%r seems pretty good in my estimation.

If you were chronographing a load and your average velocity for a small sample measured 3000 fps and you worked up a ballistic table based on that measurement but the actually velocity average was 3015 fps (0.5% error, assuming all the error was in the positive direction) that would move you point of impact up by rough 3-4 inches for a decent bullet (say a ~ .5 BC (G1) give or take a little) at 1000 yards.

You may or may not agree that +/-0.5% error is good or bad but the reality is a lot of long range shooter use those instruments along with some other tricks and manage to create ballistic tables that get them hits out well beyond 1000 yards.

 

[jmorris]

I find this exceptionally interesting - Would you mind mentioning which specific cartridges and powders for which you’ve found these velocity plateaus?

With too little powder, we all know that a bullet will not exit the barrel (squib).

On the other end of the spectrum where too much pressure, more than the firearm can contain, can also result in a bullet that never exits the barrel.



Anything that exits the barrel will be in between those two examples and not linear as far as + .x grains = + y increase in fps. For any cartridge or powder I know of.

I own a number of chronographs and while I don’t think they are the “final answer” for any of my loads, they are another tool I can use to gain more knowledge than I would have without them.

If you’re just looking for a reason to not get one, hundreds of millions of people don’t and have never owned one and have lived happy lives.

 

[rdnktrkr]

Is the .5 accuracy between shots or is it .5 off either high or low each shot?
1% of 3000 would only be 30fps (.5% high 1st shot and .5%low second shot) I know everyone is wanting lower #s than that but for my shooting so far that is acceptable.

I used one and found my fps was lower than what I expected from the #s in the reloading manual, it didn't matter much at 100yrds but at 300 & 600yrds when I was using Strelock to figure my dope it would have.

 

[reddog81]

Is the .5 accuracy between shots or is it .5 off either high or low each shot?

+/- .5% would mean it could be .5% off in either direction. For a 3000 FPS load you could be 15 FPS high or 15 low for a total spread of 30 FPS. I would have to assume most readings will not be .5% off. The actual spread would be much lower on average however you never know which shot is reading high or low or by how much...

I looked at a couple samples yesterday to see what was being advertised. The $125 model I looked at had .5%+/- and the $200 model had .25% +/- listed. Realistically, I think for $125 invested .5% is outstanding. You can't expect top of the line performance for dirt cheap.

 

[denton]

Only The Almighty gets perfect information. The rest of us have to make do with anwers that are approximations, some better than others.

A chronograph is an extremely useful tool.

How well can you estimate SD with a .5% chronograph? Probably pretty darn well.

Most of the error in a chronograph is systemic error, not random error. Ken Oehler has commented that most of the error comes from the position/aim of the photosensors. So the error will bias the readings up or down a bit (accuracy) but not add to the spread of the readings (precision).

It is possible to measure the random error in a chronograph by putting two identical units in line and shooting through both. With a little math, you can extract the random error. I have done that experiment with two Shooting Chronys. The random error was small, just a bit more than 1 FPS, IIRC.

 

[mcb]

I find this exceptionally interesting - Would you mind mentioning which specific cartridges and powders for which you’ve found these velocity plateaus?

Slow powders, light bullet for caliber/cartridge and short barrels will sometime result in a near plateau of velocity. A nice example isH110/W296 in 357/41/44 Mag in a short barrel revolver with light for caliber bullets. Increasing charges result in nearly negligible velocity increases while the fireballs just keep getting bigger and bigger.

 

[denton]

AA2520 in a 308 produces a velocity plateau at charges near maximum. A magnum primer pushes the plateau out a bit. I doubt that pressure increases as velocity flattens.

I've recorded this in a couple of different cartridges, but the data is old enough that I don't remember which offhand.

 

[jmorris]

Slow powders, light bullet for caliber/cartridge and short barrels will sometime result in a near plateau of velocity.

If you look at a small enough section of a curve that section will look like a straight line. We know that there is some amount of powder that won't even push the bullet out of the barrel and cases where another amount can blow the gun up, both 0 FPS results. Somewhere in between the two there can be a spot that looks linear despite knowing that it is not.

The “max/min” loads listed in manuals are generally in this area.

 

[Varminterror]

Plateaus I get regularly, just never an asymptotic “ceiling” of diminishing returns.

Without implying anyone SHOULD exceed max book charge weights, I’ve generally found that adding more powder to push through the node at the max charge is not a “diminishing return” but rather the same velocity node we’d see in the middle of a published band of data. As long as the rifle survives the pressure, (which they do, since max pressure standards are no where near destructive limits of the design), we see velocity climb again once we pass through a node.

I’ve heard a lot of folks over the years talk about “more powder but no more speed,” as an indication of max charge, but after exceeding that a handful of times, I’ve noticed it’s just another node, not a true ceiling. Overpressure? Almost certainly. Diminishing returns? Eh, not typically moreso than any other section of the curve.

 

[.45Coltguy]

I have used/use a chrnograph, probably not as much as others. Simple use for me is velocity check as to what a manual or three are listing. Have found something interesting to me, is the correlation between standard deviation and accuracy is like comparing asphalt to trout. [Read that someplace, I think]. I could have a bit high SD, but, fantastic accuracy and just the other way around. I simply don't put too much stock in SD. There are other variables in play. Someone mentioned earlier that most shooters don't use a chronograph. I'm leaning that way, as my loads are proven already. Just my thoughts on this.

 

[mcb]

If you look at a small enough section of a curve that section will look like a straight line. We know that there is some amount of powder that won't even push the bullet out of the barrel and cases where another amount can blow the gun up, both 0 FPS results. Somewhere in between the two there can be a spot that looks linear despite knowing that it is not.

The “max/min” loads listed in manuals are generally in this area.

You can pick a powder that is impossible to blow a gun up with. Put a really slow rifle powder in a 38 Short Colt and you can't physically get enough in their to generate pressures high enough to damage the gun even if you compress it.

I am saying that in a short barrel revolver H110 (and similar powders) with a light for caliber bullet will hit a point were increasing the powder charge will result in almost no measurable increase in velocity (you just burn more powder in front of the muzzle) and this will stay like that right up to the point were you start to compress the charge when the pressure will spike and you will again see an increase in velocity and danger. No doubt the increased charge does increase the velocity but it is no longer linear, the slop is rapidly decreasing through this region of the charge vs velocity curve so any gains are small enough that any increases can be lost in the other sources of error as you shoot your test loads across a chrono.

 

[denton]

To mcb's point, with AA2520 in a 308, increasing charge increases MV in a nice orderly way, up to a point. When the plateau point is reached, average MV ceases to advance, and individual MVs become more erratic. It is not a matter of looking at too small a piece of the curve. The plateau is very distinct.

I suspect that this is the mechanism: Initially, the powder granules are in contact with each other, and ignition is passed from one granule to another. As the bullet starts to move, not all granules are in contact, and the temperature of the propellant gas is not enough to ignite them. So you get unburned powder. How much powder is unburned is probablistic. So the resulting MV varies.

 

[lordpaxman]

Unless I am completely lost in the specs or I misplaced some decimal points somewhere , I think the chronos are just useless, no?

If you get involved in some competitions, you have to make a certain power factor that is determined at the match with your ammo and gun, and a chrono. For me, it’s not useless. It does have limitations and they vary between the various technologies used to determine MV. For rifle, for me, it gives me a starting point to enter V in a ballistic app. As to it’s accuracy and precision, well, SDs are useful to some degree.

 

[denton]

A chronograph is one of the most useful measurement devices that a reloader can have.

First, it lets you see whether you are in a plateau, and need to back down or switch to a magnum primer. There is nothing to be gained, and some to be lost by operating in the plateau.

Second, it's a check on chamber pressure. MV is highly correlated with peak chamber pressure. If you are using the "book" bullet and powder, and have compensated for "book" barrel length, then if your MV is at or below "book" MV, your peak pressure is at or below "book" pressure.

Third, if you want to model your exterior ballistics, you need you MV.

Many of the calculations that got us to the moon were done on slide rules (2 significant digits), based on analog measurement equipment good to 1 or 2%.

 

[GeoDudeFlorida]

View attachment 1096732

Plateaus I get regularly, just never an asymptotic “ceiling” of diminishing returns.

Without implying anyone SHOULD exceed max book charge weights, I’ve generally found that adding more powder to push through the node at the max charge is not a “diminishing return” but rather the same velocity node we’d see in the middle of a published band of data. As long as the rifle survives the pressure, (which they do, since max pressure standards are no where near destructive limits of the design), we see velocity climb again once we pass through a node.

I’ve heard a lot of folks over the years talk about “more powder but no more speed,” as an indication of max charge, but after exceeding that a handful of times, I’ve noticed it’s just another node, not a true ceiling. Overpressure? Almost certainly. Diminishing returns? Eh, not typically moreso than any other section of the curve.

What happened there between 42.4gr. and 42.2gr.? It looks like more powder resulted in less velocity. I must be reading it wrong.

 

[Varminterror]

What happened there between 42.4gr. and 42.2gr.? It looks like more powder resulted in less velocity. I must be reading it wrong.

Happens all of the time. Not typically as steep as the grey series in that graph, but flat spots and even dips like that are the premise for defining nodes, whether it’s depicted through this Satterlee velocity curve, or Audette Ladders, or Newberry arrays.

Read up on “positive compensation” as a primer for this particular rabbit hole.

 

[GeoDudeFlorida]

Happens all of the time. Not typically as steep as the grey series in that graph, but flat spots and even dips like that are the premise for defining nodes, whether it’s depicted through this Satterlee velocity curve, or Audette Ladders, or Newberry arrays.

Read up on “positive compensation” as a primer for this particular rabbit hole.

So, adding more powder didn't add any velocity, in fact it went backwards. Gee, that sounds familiar...

Thanks but I observed it a while back in rifles and handguns, too. IMR 4227 with the old Speer 140gr. SJHP in a 4-5/8" Ruger Blackhawk. At max. per IMR's manual. A compressed load (18.5gr.) was the same velocity as the recommended starting load of 15.5 and lower than max of 17.2gr. I don't recall how much lower since I lost those notes almost forty years ago but it's why 14.5gr. of 2400 became my standard .357Mag load for the old Speer 140. Sometimes adding more powder doesn't result in more velocity. QED. Speer recommended running those SJHP and SJSP bullets at near-max charges because some folks claimed under-charges and slower velocities would stick the jacket in the barrel. I never saw that but figured I wanted bigger holes and harder hits so I'd run them fast. IMR 4227 is a good powder for that but it needs more barrel. 2400 is a really good small-bore rifle powder and about ideal for that kind of thing. Unique will also hit peak speed with a small bore, light bullet in a short barrel before you hit case fill but it's harder to see on a chronograph before you also start having problems like sticky cases and leaky primer pockets. Experiment a little more and you'll figure out how and why these things happen, I'm sure.

 

[Varminterror]

So, adding more powder didn't add any velocity, in fact it went backwards. Gee, that sounds familiar...

Note what happens a couple tenths higher - the velocity continues increasing once the node is exceeded.

Again, study up on positive compensation and long range load development methods. These flat spots aren’t indications of “diminishing returns,” for increasing charge weight, but rather indication of a localized node within the barrel’s natural harmonics.

Reaching and exceeding case capacity is certainly an issue - if more powder won’t fit into a case, then more powder can’t be added to define the top end of the node and see the continued increase in velocity as we break out of the top end. Albeit a bit apples and horseshoes to rifle cartridge loading with ample case capacity, I’ve not personally been able to see flat spots in velocity with H110 in revolver cartridges either, the more I crunch, the faster the bullets go.


But you’re defying physics to talk about increasing pressure without increasing velocity, with the only exception being these narrow node windows, not an absolute ceiling. Unlike yourself, I’ve not found many means of defying physics. QED.

 

[JFrank]

I don’t worry about the +or- percentages, there are many threads on many forums that compare chronographs and most are very close to one another and my take away is that they are under promising and over delivering. Don’t get axle wrapped living by numbers alone - targets matter..

On another note a barrel is an osculating whip tossing bullets in all direction as they come in and out of tune, as barrel exit timing becomes optimized these round began to impact the same vertical plane, we call that a node.