Chronograph accuracy

[MarkCO]

Never said you were making it up, just that you have missed some things in your understanding. Cheers.

[hounddawg]

Hornady has a interesting page on how they calculate the Bc of som eof their bullets based on range which affects average velocity

https://www.hornady.com/support/ball...les%20approach.

Hornady now publishes “200 yard” Mach 2.25 (2,512 fps @ ICAO Standard Atmosphere**) G1 and G7 Ballistic Coefficient (BC) numbers for all A-Tip®, ELD-X, and ELD Match bullets. Mach 2.0 (2,233 fps @ ICAO Standard Atmosphere) and Mach 1.75 (1,954 fps @ ICAO Standard Atmosphere) BC values are also available

and how they are converting to drag coefficient numbers with their 4DOF ballistic calculator


https://www.hornady.com/team-hornady...lators/#!/4dof

[MarkCO]

Yes, Hornady has been pushing the goal posts to a better place. I like what they have been doing.

[cdoc42]

I have to tell you guys, I am rolling over with laughter and pain in my midsection from reading this intellectual sparring between MarkCo and Unclenick. Let me be clear, I am laughing at myself for the paucity of knowledge I have on the subject, yet I, fortunately, have not blown myself up over the years I have been reloading. But this is from a guy who didn't learn much in Physics in high school because the teacher scared the shorts and skirts off all of us, and I flunked Physics in Pharmacy school because I hated the teacher. But I made in through a make-up Penn State engineering course, but only because I convinced the Prof I just had to pass to get back into Pharmacy. Following that I decided to go to Med school and I guess I made it through because I didn't have to take Physics again. Maybe you can all see how that melts together to have me ROLMAO.....

[hounddawg]

I lost interest in going all anal over chrono numbers a year or so back. One day I noticed that generally the best groups had the best numbers at 100. I also noticed that the best groups at 100 were also the best loads at 600 - 800 and never did a bad group at 100 turn into a good group at 800. Now my only interest in chrono numbers and BC's is to get me on paper at long range. Once on paper I can make small scope adjustments to get me centered and the groups tell me everything I need to know about the load.

I have used my chrono more lately playing with Gordons Reloading Tool and OBT, but that is more a intelectual amusement on the computer more than anything that helps at the range

[The Happy kaboomer]

My Oehler 35P cronograph is around thirty years old. Still works like new. Gives 2 velocities for each shot(3 sky screens). If there is a major variation it flags it as a bad shot. There is NO cronograph out there I would trade it for. Has built in printer that prints your data as it is shot.

[mehavey]

I have both the trusty old Oehler and the New-Fangled LabRadar.
Wouldn't trade either, but it's LabRadar that goes to all the dances now.
Burma Shave

[mehavey]

Need to emphasise:

If you
- Don't handload to any significance
- Don't depart from exclusive use of published data in powders, bullets, OALs by using the likes of QuickLoad/GRT, etc
- Don't use cast bullets where loading/ballistics data can be unusually sparse.
- Don't need to evaluate group performance at same time as internal/external ballistic performance
- Don't need, want or use honest/actual ballistic coefficients to extrapolate longer-range use (without said long ranges available ahead of time). . . .

...pretty much any chronograph will do.
Don't waste the XMas fund on the likes of LabRadar.

[hounddawg]

a good article on how bullet BC will change from rifle to rifle and even bullet to bullet

https://precisionrifleblog.com/2019/...in-ballistics/

and another on why if you plan on shooting past 100 yards you should use G7 BC's instead of G1

https://precisionrifleblog.com/2019/...m-drag-models/

and if you really want a accurate chrono out to 1500 meters, pony up 100K and get one of these

https://www.infinition.com/en/product/br-1001/

[Unclenick]

Originally Posted by cdoc42

I have to tell you guys, I am rolling over with laughter and pain in my midsection from reading this intellectual sparring between MarkCo and Unclenick

You are about to laugh harder when I tell you we weren't talking about the same thing. My post #13 was about the number published on the box. My first two sentences were:

Originally Posted by myself

Not for BC. BC stays the same in all conditions. When you change those other conditions you enter them in the ballistics calculator with that same BC, and the results are right.

Clumsily worded on my part. Then Mark jumped on the first sentence as saying the BC doesn't change with conditions but didn't catch my second sentence indicating ballistics software adjusts for different conditions behind the scenes. So he was talking about the BC you would have in actual firing conditions, while I was arguing the number(s) on the box won't change, that being part of the simplified ballistics approach to BCs. Talking right past each other.

If ballistics published individual atmospheric condition BCs, each bullet maker would have to issue a matrix of values for atmospheric condition combinations and people wouldn't be able to easily compare bullets and most probably wouldn't bother to learn to use such a set of tables anyway. Nonetheless, the discussion is useful for describing how the numbers could possibly be off on a box, bragging rights for the bullet maker notwithstanding.

In 1881, the Gavre Commission proposed the idea of adopting a standard atmosphere for firing tables, and all measurements taken in other atmospheric densities were then adjusted to show what those measurements would have been in the standard atmosphere. This is a simple adjustment to drag made by multiplying it by the ratio of the test air density to the standard atmosphere density. So this adjustment has been SOP for a long, long time, and the Ingalls tables from circular M and all such late 19th century published data were set up that way for artillery officers to work from. The fly in the ointment is the definition of a standard atmosphere has suffered from a bit of creep.

According to Sierra in 1978, when the Second Edition of their data manual was printed, the most common practice in the industry was not to measure anything directly at all. Instead, they used charts of bullet nose shapes published in 1936 by Wallace H. Coxe and Edgar Beugless, two of DuPont's staff ballistics engineers. You would lay your bullet down on the chart and see which outline matched it best, then go look up the shape factor for that nos to divide into your sectional density to get the BC. It was supposed to give a standard atmosphere G1 BC. In 1936, the standard atmosphere would likely have been U.S. Army Standard Meteorological conditions or something similar. Today we use the ICAO standard atmosphere, which is about 1.836% denser than the U.S. Army Std. Metro. atmosphere, so U.S. Army Std. Metro BCs are about 1.01836 times larger than ICAO BCs, as the same shape glides further in the thinner U.S.Army Std. Metro. air.



The ICAO standard atmosphere was first published in 1993. So when I look at Sierra's 1978 single BC number the 168-grain MatchKing, it is 0.474 for a velocity of about 2525 fps. If I divide that by 1.0836, I get 0.465, meaning the measurement they took then would give a BC of 0.465 in the ICAO standard atmosphere, and that is close to the 0.462 they give today for 2600 fps and up. So Hounddawg was right in post 12, provided what you compare pre-1993 BCs to later ones, as the standard practice of adjusting to the standard atmosphere does not take into account the standard atmosphere changeing different. It certainly is one factor lowering the numbers, but improved measurement precision accounts for a lot, too. The continuous velocity vs. time output of Doppler radar giving the highest resolution.

Sierra didn't publish multiple BCs at different standard atmosphere velocities for the 168-grain SMK back in '78, though they had just started to do it with a few of their hunting bullets. In 1969, with access to their first exterior ballistics computer program, they had begun using the method of recording muzzle velocity and time of flight to a stop screen about 50 yards away, as had some others in the industry. This explains why the single BC given on a box of bullets tends to reflect the value at a typical muzzle velocity in data.

[hounddawg]

I still think the best way to get a accurate BC to work with for any given bullet/rifle combination is to shoot it at various distances out to the maximum range you plan on shooting using the published BC, then measure the average point of impact vs the point of aim and adjust the published BC up or down slightly until the points of impacts fit the real world results using the ballistics program of your choice

but then what do I know, I am just a old hillbilly with a public school education

[Unclenick]

The high-power military-grade Doppler radar will still be best because the continuous velocity numbers for all points in time eliminate any guessing at best breakpoints in the values. But, as Litz says, even a box of match bullets can exhibit 3% variation in BC, so there's a limit to how precise it is useful to be with BCs. Plus, I, for one, can only access a 1000 yard range occasionally, so I need workarounds.

I saw an argument between Bryan Litz and a European shooter who was a member of either a police or military sniper unit. This was on another forum some years ago. The European's outfit used equipment that used something akin to or evolved from Art Pejsa's method that he published in Precision Shooting toward the end of that magazine's life. I recall they were firing to measure drop at half their maximum range to fit data to project drop at other ranges, which is was what I recall Pejsa describing in that article and which he claimed would get you drop within half an inch at 1000 yards. The European's argument was that BCs were antiquated and less accurate by comparison. Of course, he only had to worry about one bullet fired from one gun. If you want to make the information portable, BCs are still, by far, the most compact ballistic information.

I think that argument must have been over ten years ago. Smartphone memory and computing capacity have grown so much since then as to gradually obsolete tables and they have the capacity to use the individual bullet drag functions determined by Doppler radar. Lapua has made those functions available for its bullets for over a decade and Hornady is now generating them for other brands, especially its own.

[hounddawg]

My max range is 850 yards locally but I have always been able to get on the 18" gong there after zeroing at 100 and using my Prochronos velocity reading and manufacturers supplied BC. Horizontals from wind give me more grief with that than verticals. You can have a lot of different wind values over a half mile

Now if I start shooting Rimfire PRS I will do the 25, 50 100, 200 yard drop measurements and use the ballistics calculator method for truing the BC for the determining drops for 185 yard, 65 yard etc shots

[Colorado Redneck]

Tried the unit again today. Set it up 25 feet from the front of the shooting bench. First up was a .204 Ruger that has been rock solid consistent, and the two rounds over the chrony were pretty much spot on. Next up was my 222 Remington which was the rifle I had really goofy results with before. The first few rounds were looking like they were in the ball park. Then velocities displayed jumped about 100 fps, and became more erratic. So, a deer rifle (243) was next. First two rounds the velocities were similar to several different range sessions a few months ago. Then sure enough, displayed velocities went higher every round for 5 rounds. So, to hell with it, the unit can't be trusted, and it's headed to the landfill.

I really enjoyed the discussion in this thread, and thanks to all for the comments.

[Unclenick]

That pattern is pretty suspicious. Sounds like something is warming up and ceasing to work properly. Unless the manufacturer will fix it for a reasonable price, I think the landfill makes sense.

[berettaprofessor]

I always bring a 22lr along for a sanity check.

The most practical advice I've seen in quite a long while.....

[Unclenick]

Yes. I think Dr. Ken Oehler uses a BB gun as a check, too, but I've forgotten the reason for that choice. The 22 LR in a rifle barrel is a good choice because the powder all burns up inside any barrel of about 18" or longer, and the expansion ratio is so large, individual chamber differences have little effect. Past about 18 inches, bullet velocity changes very little. Even at 24" velocity is about the same. So if you use match ammo, it will generally achieve the number stated on the box within 50 fps.

[hounddawg]

two rounds over the chrony were pretty much spot on. Next up was my 222 Remington which was the rifle I had really goofy results with before. The first few rounds were looking like they were in the ball park. Then velocities displayed jumped about 100 fps, and became more erratic. So, a deer rifle (243) was next. First two rounds the velocities were similar to several different range sessions a few months ago. Then sure enough, displayed velocities went higher every round for 5 rounds.

Something does no add up here. You do not mention turning the chrono off when you switch rifles and say the first few rounds from each rifle were what you expected. Seems to me though is if it were the electronics warming up causing abnormal readings the second and third rifles would display abnormal readings from the first shot.

[Colorado Redneck]

Hounddawg....I know. Baffling.
I was suspicious that the 222 wasn't getting complete powder burn so took the chrony out 25 ft. That isn't the issue. However, the problem no longer exists.