Statistics- what does and doesnt matter.

[Erik Cortina]

Low ES is the key to LR accuracy.

I develop loads at 100 yards and use an Oehler 35 Chronograph to evaluate a load. If load groups good at 100 yards and had a low ES, it will shoot at 1000 yards.

I did not trust my chronograph numbers until I bought the Oehler 35. The only other chronograph I would trust is the PVM-21. I've heard good things about the magnetospeed, but I would never strap anything to my barrel for load testing and then pull it off when done. Consistency = accuracy.

 

[WyleWD]

I would expect that the greater the screen separation, the more reliable the data. Do any of you have any information on this?

Boyd - yes, the greater the screen separation, the more reliable the data.

Who (or what entity) makes this claim?? Not disputing it, but the farther from the muzzle the reading is taken then the less it becomes actual "muzzle velocity". Right? :-\

This is interesting reading on this site regarding chronographs........ WD http://www.precisionworkbench.com/support-4.html

 

[BradY]

Erik- I shot with the magnetospeed on and at 300m the only difference with it on and off was about 1-1.5 inches in elevation of the group. The vertical spread of the two groups stayed very similar. Again and its a weakness I know, I didnt repeat this or shoot strings of 10-15 shots (only 3 as thats all I had loaded at the time) A buddy shooting his 223 next to me had the same experience while trying some 80.5gr berger fullbores.

Something further to test when the opportunity presents itself. I dont think it would make too much difference at 100yds but I wouldnt use it at 1000yds and expect consistant results.

Since you prefer to use ES more so than SD, what sort of spreads do you look for in a load to produce X ring vertical at 1000yds?

 

[bigedp51]

Prehistoric man hunted wooly mammoths with spears without the aid of a chronograph.

In the late 1800s the Buffalo was hunted to near extinction without ES and SD.

Conclusive Statistical Analyses of this subject:

You don't need a chronograph, you just need bigger targets covered with dirty smelly hair. :

 

[bdale]

I personally don't know what to make of it but last week I was testing some loads for hunting season coming up and had loads with SD's as low as 5 and had other loads with SD's like 12 or 15. Funny thing was the higher SD's were shooting in the same hole practically while the lower SD's were giving me 1.3 to 1.5 inch groups so I'll shoot what the gun tells me to.

 

[BoydAllen]

Uniformity of velocity should not be confused with being in tune. For long range you need both. For short range, you pretty much only need to be in tune.

 

[GSPV]

Being in tune means being forgiving of various kinds of inevitable "slop" including velocity.

If your tune is getting to an edge of the window and you have a velocity error beyond that edge, it ain't a gonna go in the group.

Addendum: Added this post only to clarify for newer folks. It's not meant to contradict information others have provided.

 

[BoydAllen]

I guess that what I should have said was that I have seen some loads that looked really bad over the chronograph that shot really well at 100 yd. but I don't think that would be possible a 1,000.

 

[jlow]

I would expect that the greater the screen separation, the more reliable the data. Do any of you have any information on this?

Boyd - yes, the greater the screen separation, the more reliable the data.

Who (or what entity) makes this claim?? Not disputing it, but the farther from the muzzle the reading is taken then the less it becomes actual "muzzle velocity". Right? :-\

This is interesting reading on this site regarding chronographs........ WD http://www.precisionworkbench.com/support-4.html

I think you misunderstood what I said. We are NOT talking about distance from the gun to the chrony but distance between the detectors on the chrony. With the Oehler, it has three screens which gives you two separate readings. The machine is setup so that the distance between the screens can be changed by using longer rails that they are mounted on i.e. 1’, 2’, 4’, and 8’. And yes, it says right there in the manual that “The expected error on any one shot depends on both velocity and screen spacing” So the expected error for a bullet moving at 3,000 fps for the above rail lengths will be 16fps, 8fps, 4fps, and 2fps.

 

[BoydAllen]

Thanks for the additional information. So, based on that, the guys that want reliable readings for critical long distance load testing should probably have their screens 8' apart. The thing is, even if your chronograph does not have that provision, if the screens are rail mounted rather than integral with the unit, you could jury rig the same thing, it is just that you would have to use a multiplier to calculate your velocities.

 

[WyleWD]

I would expect that the greater the screen separation, the more reliable the data. Do any of you have any information on this?

Boyd - yes, the greater the screen separation, the more reliable the data.

Who (or what entity) makes this claim?? Not disputing it, but the farther from the muzzle the reading is taken then the less it becomes actual "muzzle velocity". Right? :-\

This is interesting reading on this site regarding chronographs........ WD http://www.precisionworkbench.com/support-4.html

I think you misunderstood what I said. We are NOT talking about distance from the gun to the chrony but distance between the detectors on the chrony. With the Oehler, it has three screens which gives you two separate readings. The machine is setup so that the distance between the screens can be changed by using longer rails that they are mounted on i.e. 1’, 2’, 4’, and 8’. And yes, it says right there in the manual that “The expected error on any one shot depends on both velocity and screen spacing” So the expected error for a bullet moving at 3,000 fps for the above rail lengths will be 16fps, 8fps, 4fps, and 2fps.

I understood exactly what you said......... and you answered my question. Thanks. WD

 

[GSPV]

I guess that what I should have said was that I have seen some loads that looked really bad over the chronograph that shot really well at 100 yd. but I don't think that would be possible a 1,000.

Absolutely.

 

[Erik Cortina]

Erik- I shot with the magnetospeed on and at 300m the only difference with it on and off was about 1-1.5 inches in elevation of the group. The vertical spread of the two groups stayed very similar. Again and its a weakness I know, I didnt repeat this or shoot strings of 10-15 shots (only 3 as thats all I had loaded at the time) A buddy shooting his 223 next to me had the same experience while trying some 80.5gr berger fullbores.

Something further to test when the opportunity presents itself. I dont think it would make too much difference at 100yds but I wouldnt use it at 1000yds and expect consistant results.

Since you prefer to use ES more so than SD, what sort of spreads do you look for in a load to produce X ring vertical at 1000yds?

The fact that there is difference from magneto speed on or off should be reason enough to not work up loads with it on.

20 ES is good, 10 is exceptional for LR.

 

[Lapua40X]

IMO, the reason that many shooters rely on ES rather than SD is that ES can be calculated with a simple caliper - at least as long as your not trying to work with it from a standpoint of probabilities.
SD requires working with this, making it considerably more difficult.

 

[Erik Cortina]

IMO, the reason that many shooters rely on ES rather than SD is that ES can be calculated with a simple caliper - at least as long as your not trying to work with it from a standpoint of probabilities.
SD requires working with this, making it considerably more difficult.

I use ES because it's the only one that matters, simple as that.

So, how do you measure ES with a caliper? All this time I've been using a Chronograph!

You should invest in a different chronograph other than what Wal-Mart sells, they will calculate SD for you, no need to know the formula. ;D

 

[Webster]

The chronometer only measures the bullet speed. Accuracy depends on the whole system. You mentioned a a small ES with a big group. If you buy a lot of high quality bullets they cannot all be exactly identical. How critical is 0.0000I" variation in jacket thickness at 300,000 RPM, jacket bonding, metplate and ect.? Is the next step to preflight test them. Build something like a miniature tire balancing rig. Spin each bullet up to 25-50000 RPM and check for imbalance.

 

[jlow]

Thanks for the additional information. So, based on that, the guys that want reliable readings for critical long distance load testing should probably have their screens 8' apart. The thing is, even if your chronograph does not have that provision, if the screens are rail mounted rather than integral with the unit, you could jury rig the same thing, it is just that you would have to use a multiplier to calculate your velocities.

Boyd, it really depends on your situation and needs. For me, a 4’ rail serves me best since I can use a single tripod, easy to assemble, it still fits in my truck, and the accuracy is still good enough. The 8’ rail requires 3 tripods and is a real hassle to set up. I suppose if I was lucky enough to have a range at the back of my house I might consider it but….

BTW, this is one reason why the shooting chrony has a limited accuracy i.e. because their detectors are only 1’ apart where as the ones mounted on my 4’ rail are 2’ apart.

 

[Steve Blair]

BTW, this is one reason why the shooting chrony has a limited accuracy i.e. because their detectors are only 1’ apart where as the ones mounted on my 4’ rail are 2’ apart.

[br]
There are three major factors affecting chronograph accuracy. [br]
1. Triggering - How consistently do the screens register a bullet event?
2. Sampling rate - How many times per second does the system check for an event?
3. Screen spacing - Reduces error as a percentage of velocity. [br]
Some modern chronographs address all three areas and produce accurate, consistent results. Some produce results as previously described that give a good idea of the average velocity, but not much more. Caveat emptor.

 

[jlow]

Agreed! But in general, I think the shooting chronys are for general use but I don’t think for precision results. The reason I say this is not to slam the shooting chronys since they are in fact a great bargain, but they do have a short 1’ rail and the way they deploy (unfolding) precludes an ability to have an accurate and straight distance between the detectors. You can visually see this because the two halves don’t always sit flat…. If you don’t have a known, reproducible distance between the detectors, I doubt we can expect very accurate reproducible results to the degree that the precision shooters need.

The other advantage of the Oehler is of course they give you two results which can be used to detect artifacts. Not foolproof but certainly always better than a single sample value.

 

[Lapua40X]

I use ES because it's the only one that matters, simple as that.
So, how do you measure ES with a caliper? All this time I've been using a Chronograph!

I apologize, Erik. Looks like attempt at a bit of humor fell flat. :-X