Is a chronograph necessary?

[Arboreal]

That is what I asked Blaine Fields a while back and I thought his answer was interesting so I asked permission to make it
public.


[email protected] wrote:

Hi Blaine, I have a question that has been bothering me. Is there any need for a chronograph if I use your program to determine MV? I shot mine a while back (trying to determine BC) and seem to be doing fine with just the MV calculator in FFS and the Brian Litz book of "real" BCs. I am starting to teach long range shooting classes and I thought I would ask you what the pro/cons are of not using the chrony at all. I don't understand the need for a high end chrony for sure as we are still taking the POI method as the truth in the end. It is nice when I can use my buddy's cheap chrony to get a ballpark MV though. Thanks for writing such a great program. I think I will be upgrading mine as soon as I can get a Nomad. I have the Pharos which I understand has a hard time running the latest version. Nathan

On 2012-12-05 20:01, Blaine Fields wrote:

I think you've got the right idea. A chronograph is nice to get an idea of velocity but truthfully I don't trust any of them. A friend and experimenter in Australia tested two PVM-21 units in tandem and found the two to be 20 fps apart. I was a little shocked by this. I figured that given the price of these units they would be within 1 or 2 fps of one another. Currently I am testing a unit called the MagnetoSpeed which hooks directly to the end of the barrel. It seems to work well, isn't affected by sun light, rarely, rarely, rarely misses a shot, and is a lot more convenient to use. Costs about $250 and works as well as the PVM-21 as far as I can tell. The only downside is that attaching the unit to the barrel changes the point of impact so you can't zero and get velocities at the same time. The only thing to look out for when calculating a MV is to make sure that the zero is as perfect as you can get it and to subtract any error in the zero from the results at range before starting the calculation. In other words, if you are a 1/0" high at 100 yards and can't get any better due to the fact that the scope can only dial in whole clicks, just remember that at 600 yards that 1/10 inch has become approx. 6/10 of an inch. Convert the error to an angle, recognize that the angle error exists at range and subtract it before working the balance of the calculation. In my opinion you will get a more accurate muzzle velocity from the actual trajectory than with a chronograph. But you have to make sure that the trajectory was not moved up or down due to wind effects caused by the topography. If you have a true unaffected trajectory you will get a very accurate muzzle velocity. At that point, the chronograph is just used for down and dirty approximate numbers. Blaine L. Fields Lex Talus Corporation 9120 Double Diamond Pkwy Suite 6001 Reno, NV 89521 775.434.0420 [email protected] www.lextalus.com On 12/5/2012 2:47 PM,

 

[stranded]

Re: Is a chronograph necessary?

HG, I think Blaine is right but unless someone can eliminate all variables(shoot perfectly everytime) how can they trust what the bullet is showing? I like the idea of an inexpensive chrony just for ballpark figures,nothing beats actual data for each yardage,right?

 

[Graham]

Re: Is a chronograph necessary?

Chronograph data is not a substitute for collecting actual data because muzzle velocity is not a fixed value and BC changes as the bullet slows down. That said, you need to chrono because you have to start your calibration somewhere.

FFS gives you a maximum supersonic range based on a drag curve and initial muzzle velocity. To find the point at which the bullet is at 90% of its supersonic range you need an initial muzzle velocity value and you need to calibrate the program.

Calibrating the program means adjusting its output to actual observed results. You use a chronograph to get a starting point for muzzle velocity, then you measure the drop at a minimum distance in order to adjust the muzzle velocity/BC in FFS until the program provides accurate outputs for all ranges up to that maximum distance.

 

[Bullet Molester]

Re: Is a chronograph necessary?

A shooting buddy of mine and I were debating needing a chrono recently. We were having trouble with elevation consistency for him based on ballistics programs. We started with our "expected" MV, then worked our way plugging slower MV into shooter and JBM programs, until we settled on a lower MV that had the trajectory match what he was actually shooting at 100-800 yards that day. His barrel is shorter than average and we ended up at 2460fps (I believe) on that ammo from a 20" piped .308 with 175 grain MK BTHPs. I'm assuming the data was pretty close since his actual impact curve was practically perfect with the projected data at this velocity from two programs.

 

[Tacticalrum]

Re: Is a chronograph necessary?

I would have to agree. If you make an educated guess and then validate you don't really need one.

 

[jerry1]

Re: Is a chronograph necessary?

You can work around the lack of a chrony. In the end you are going to be judging true drop anyway. However a chrony is nice to make sure a given load is giving you the speed you want. No sense shooting a 300 WM and if you are only getting 06 speeds.

 

[SnkBit]

Re: Is a chronograph necessary?

Although noticeable in long distance groupings, the chrono will more easily show extreme spreads. Also, it's much quicker and easier to work up to your desired velocity with a chrono. Once you find your desired load use actual drop to determine a more true velocity.

Necessary? No. Helpful? Absolutely.

 

[-Fabien-]

Re: Is a chronograph necessary?

You can shoot without this expensive device, but you'll always miss this so important information, the speed of your bullet...

 

[tarzan]

Re: Is a chronograph necessary?

just shoot at 300 yrds get my up and down 1 in or less and call it good

 

[lanwickum]

Re: Is a chronograph necessary?

No, it is absolutely is not. I have a oheler 35p and a magnetospeed. I hardly ever use them. Get good dopes. The proof is in the pudding. I use a ballistic calculator and have targets out to 800 yards. Can set targets at any range to about 3 miles within a few miles from my house. Never had any better luck using chronograph speeds over predicted speeds. If impacts and calculations do jive together then you got it correct. You should be able to project your velocity from your dopes. The chronographs just make it quicker to get the velocity. I agree with Blaine 100%.

 

[Belisarius]

Re: Is a chronograph necessary?

It surely adds to the fun

 

[rg1911]

Re: Is a chronograph necessary?

Well, my riflesmith said I'd want to get the MV above a particular point. My Oehler 35P kindly told me when I had hit that point so I then could tweak the load. I'll assume he was right, since the new barrel is proving to be a tack driver.

Possibly not necessary, but useful.

Richard

 

[gstaylorg]

Re: Is a chronograph necessary?

Absolutely necessary? Probably not. However, for those that don't have access to longer ranges for practice, the first time you show up at a 1000 yd F-Class match with a new rifle and/or load and don't know your MV, I'll bet you'll be wishing you had a better drop prediction.

I use my MagnetoSpeed routinely and it has allowed me to be within a very few elevation clicks (0.125 MOA turrets) of center X-ring when traveling to competitions at different locations having a very wide range of different elevations/atmospheric conditions. I appreciate not having to waste a lot of rounds during sight-in at a match trying to get my elevation dialed in. That way, I can focus my attention on windage as the more important factor score-wise. So I think a lot depends on the type shooting you plan on doing as to how critical having solid MV information beforehand will be.

 

[Timo Turl]

Re: Is a chronograph necessary?

It depends what you are trying to achieve. I shoot a variety of bullet/brass/powder combinations in several calibres in addition to factory ammo. While I know that I probably should, the reality is I don't always shoot them all to 1k over 100-yrd increments and record actual dope in a variety of conditions. I would be forever going back and forth/recording data.

Once I do have a load I like and I have my theoretical and actual dope then I still use a chrono. I might have loaded and tested in the summer and knowing my velocity in different climatic conditions is nice to have.

 

[Jedi]

Re: Is a chronograph necessary?

Can you do load development with out one ... sure

Can you reverse calc actual dope to get fps ... sure

Will using a chrono provide better data ... nope

ES/SD numbers will not change what the target tells you

 

[FamilyMan]

Re: Is a chronograph necessary?

I think a chron is very useful but not Necessary because there are many ways you can come to the same conclusions without one but you can just get there a little quicker with the chrono. Here is one place that I have found a chrono useful. In low visibility conditions. because in these conditions you cant really spot where you hit beyond 250ish just that you hit(or at least I couldn't last Saturday). So I couldn't really true my dope without having to shut down the range and run out to the targets and check . but the chrono allowed me to get a lot closer to actual than just guessing and then I only had to make minor adjustments when i realized I was hitting a little high. with that being said I have and use a Magneto Speed but have been able to achieve the same results and been just as accurate with out one. its just easier to do it with less work with one.
Just my 2 cents which is about what it is worth.