chronograph

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  • Last Post 08 February 2019
R. Dupraz posted this 03 February 2019

How useful is a chronograph in developing cast bullet loads ?   Worth the expense or not ?

I have just let the groups on the target tell me whether I have found a good combination or not. But have been tempted over the years to invest in a chronograph and have so far, resisted. But the temptation has once again reared it's ugly head.

R.

 

 

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RicinYakima posted this 03 February 2019

I asked about this same type of question to my brother and his friends, who are all rocket scientists at JPL. Their consensuses was that until the extreme spread of the load allows for a gravity drop of half the group diameter at the distance, it doesn't make any difference.

A 32/20 load that has a spread of 100 f/s will show up at 25 yards. A 30/06 hunting load with an extreme spread of 100 f/s will not show up until about 350 yards. The group size covers up the drop difference.

I have had two and only use them for information for articles because people seem to like statistics. IMHO, they have value for developing loads, but tell nothing about accuracy.

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joeb33050 posted this 03 February 2019

I just counted, and find that I've chronographed 208 loads in the past 18 months or so. There is NO accuracy conclusion that can be drawn from chronographed  particular loads. I write down each MV, and look at each bullet hole. Faster bullets can be higher or lower than, left of or right of, bullets of the same load. 

Bullets shot with different loads, different charges of powder DO seem to vary. 

 

 

This is group size vs. grains of Titegroup and calculated 100 yard velocity; accuracy DOES vary with powder charge/velocity.

So, it ain't variation of velocity WITHIN groups; it is the difference BETWEEN average velocities that varies group size.

Or, I haven't found it yet.

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TRKakaCatWhisperer posted this 03 February 2019

I'll say two things about measuring velocities with cast bullets.

a) I observed a person on the range chronographing loads.  He noted on his laptop the velocities, the chamber pressure, and the accuracy.  That was Bill Alexander of Alexander Arms developing the 50 Beowolf.  (PhD in physics for what that's worth.)

b) I own a chronograph.  Someday I'll get it to the range.

 

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frnkeore posted this 04 February 2019

I have a 3" tall, 3 ring binder, full of chronograph results, for many calibers. It is useful info.

I record the rifle, barrel info and all the load data. I've found the chrono to be useful in primer selection and primer size comparisons. In general, a smaller primer will produce lower velocity's, with the same powder charge.

I've found it to weed out loads and primers that produce greater ES than 30 fps. I never use a load with more than 30 fps ES as, I never found a load the more than 30 fps ES that could produce match accuracy in my velocity range of ~1450 fps.

It's also, invaluable when your working with a cartridge w/o loading data. In my case, the loading the 22RF, for breech seating, as well as my own wildcat cartridges in 30, 33 and the old Stevens cartridge, 32/35.

I was about to buy the Radarlab but, I called them and found that it will only track a 22 bullet to ~60 yards and a 30 cal to 80 to 100 yards. The reason for wanting that unit, was for measuring the BC of different bullets. It's a lot of money and I was hoping it would track to at least 100 yards with 22's as that's my shortest distance and wanted 200 yards for 30 and above.

It still might have some benefit so, I'm still thinking about it.

Frank

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John Carlson posted this 04 February 2019

I chronograph all my practice sessions and some of my matches.  That's because I'm highly enamored with gadgets gizmos and data.  I found the correlation between chronograph data and accuracy far stronger with jacketed bullets than I have with cast bullets.  Even so I do find that being able to duplicate velocity when changing bullets or powders can help me to find the sweet spot for a new load.  It can also be useful in determining the effect temperature has on powder which is sometimes significant.

Holding public office should be viewed as an obligation to serve, not an opportunity to rule.

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tony1960 posted this 05 February 2019

I tend to chronograph ant test ammo and if I have anything going through a ransom rest. Tend to take pics of groups too for future reference, sad eh?

But, in six months or a years time when I fire those groups again and it's not comparable, I have a record.

 

And seeing most of my friends are lazy and would rather use my data then go and find it out for themselves, I can show them what their gun could be capable of if they spent time at the range.

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Paul Pollard posted this 05 February 2019

Frank,

Do you need 100 yards or can you use muzzle velocity and 20 yards or 40 yards or 60 yards to calculate the B.C.? You should be able to calculate using 2 distances, not necessarily 100 yards spacing between chronographs. I also wondered about using a Labradar for calculating BC.

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Eutectic posted this 05 February 2019

I have owned 5 chronographs, the first was a Herter's powered off my car battery, wire screens a real pain to use. Velocity or groups you had to choose.

Modern ones are MUCH better. you can shoot groups and get velocity at the same time. They even do the statistics for you, great stuff.

In my experience velocity variation (high standard deviation) has to be very large to affect accuracy and small SD is no guarantee of accuracy.

If you are into experimenting or using non-canister powders you need a chronograph as well as pressure measurement! For most shooters a chronograph is not useful.

Most of the ones I see at the range are used by hunters who think a 100 foot second faster load will kill game 100% better.

Steve  

 

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Larry Gibson posted this 05 February 2019

"How useful is a chronograph in developing cast bullet loads ?   Worth the expense or not ?"

I've had 3 Oehler chronographs (M11-61, M35P & M43 PBL) since '74.  I have chronographed thousands of loads and have maintained records of the results: ES, SD and with the M43, pressure, BC and other useful information. I use the chronograph in all my load development; rifle and handgun, cast and jacketed bullets.  I've found that when accuracy testing at 100 yards and under, especially 50 yard testing for accuracy, the correlation between a small SD/ES and accuracy isn't always consistent.  However at longer ranges of 200 yards or farther I've pretty consistently found that loads having the smaller SD/ES correlation prove to be them most consistently accurate.

Of course we must understand velocity measurement at the muzzle with a chronograph is really only telling us about the consistency of the internal ballistics.  External ballistics also has a great effect on accuracy and a chronograph measurement of velocity at the muzzle does not tell us anything about that. 

LMG

Concealment is not cover.........

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frnkeore posted this 05 February 2019

Frank,

Do you need 100 yards or can you use muzzle velocity and 20 yards or 40 yards or 60 yards to calculate the B.C.? You should be able to calculate using 2 distances, not necessarily 100 yards spacing between chronographs. I also wondered about using a Labradar for calculating BC.

Paul,

Yes, you can measure BC at shorter distance but, I believe it's more accurately done measuring to the distance that you actually shoot at. I'm fairly comfortable measuring it at 100 yards, as my data from the M43 was shot at that distance and I can compare those bullets for a reference point but, I breech seat 22rf and I'd like to know the BC of the bullets I try at 100 yards, the range that I shoot most.

In CF, I shoot at 200 yards, 90% of the time and I'd like to track the BC to that distance, to test tipping and see what difference tipping (and where it occurs) and velocity change does to a bullet. Same with the 100 yard RF bullets. Lyman and several jacketed bullet makers, indicate that BC changes with velocity, I would like to know what happens, with my bullets, at my velocity's, over the range that I shoot.

At $560, I don't know if I want to limit myself to their distance. If it where 1/2 that, I would have bought one when I first heard of them!!! I'm still thinking and I may still buy one.

In my conversation with them, the guy I talked to, indicated that units could be made to track that far but, the power of the unit was limited by either the FCC or the FAA, I think the latter.

Frank

 

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JeffinNZ posted this 05 February 2019

I'm on my second Chrony as the first died after about 15 years of decent use.  These days the new device doesn't see the light of day a great deal however.  When the chronograph was VERY valuable was when I was working up subsonic loads for my suppressed .32-20 Martini

 

 

Cheers from New Zealand

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Larry Gibson posted this 05 February 2019

Paul Pollard

The Oehler M43 also measures the time of flight to 100 yards.  Comparing the TOF to the velocity lost and BC can also give an idea of the stability of the bullet.  The more a bullet yaws or wobbles the smaller the BC and the greater velocity loss it has.

LMG

Concealment is not cover.........

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frnkeore posted this 05 February 2019

The M43 can also go to 200 yards, if you have the cable but, it can not tell you anything about where and when anything happens, other than where the actual impacts happen.

The Radarlab tells you whats going on in increments as the bullet travels down range. You have to do the math for BC but, it's way more accurate for a bullets actual flight path.

Frank

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Paul Pollard posted this 06 February 2019

Larry Gibson,

Could you give an example of using time of flight and velocity lost? Do you compare it with bullet BC? My limited experience so far shows woefully low BC. I think the bullet is really wobbling.

Thanks,

Paul

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Paul Pollard posted this 06 February 2019

Larry,

I used the JBM calculators and got a real low number for BC. It helps to use yards consistently throughout the values. By putting FEET at the second velocity reading, the BC was astonishingly low! The time and distance versions work pretty close to the expected numbers now.

Paul

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shootcast posted this 08 February 2019

I think you have to be able to shoot very well before I could say that a chrony is helpful. It will tell what powder load should give you best accuracy. But my experience has shown some very repeatable groups that the chrony says shouldn’t be happening. Also some loads the chrony says is the cats meow but target shows a different story. However if your working with a wildcat and working up your own loads it will be very helpful along with normal pressure signs. You know right away what velocity your getting. If your alloy seems to perform best in a window FPS . 

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R. Dupraz posted this 08 February 2019

Ric:

" However if your working with a wildcat and working up your own loads it will be very helpful along with normal pressure signs. You know right away what velocity your getting. If your alloy seems to perform best in a window FPS"

 

The above is exactly why I started thinking about a Chronograph again. I have been fiddling with both GC and hopfully soon PB  in a custom  6mm X 223 barrel for which there is relatively scant load data, let alone cast. at least for some of the powders bullet weights that I have and would like to try.

I really don't care about all the extra numbers except for the velocity. Thought that it would be interesting to find out at what velocity range accuracy occurs. If for my own curiosity if nothing else. Also, to find out if there is a correlation between hardness, accuracy and velocity. The last time out leads me to believe that there is. 

 

R.    

 

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Larry Gibson posted this 08 February 2019

Larry Gibson,

Could you give an example of using time of flight and velocity lost? Do you compare it with bullet BC? My limited experience so far shows woefully low BC. I think the bullet is really wobbling.

Thanks,

Paul

 

Here's a fairly recent example;  It was a test of an unopened box (20 rds) of M118SB.  I shot a 10 shot test in my 14" twist .308W Palma rifle and the other 10 shots in my 12" M70 target .308 rifle.  The Palma rifle has a 27" barrel and the M70 a 26" barrel.  The tests occurred on the same day under the same conditions about 40 minutes apart. 

The M70 gave the following data;

Muzzle velocity; 2653 fps 

Down range velocity at 285 ft; 2471 fps with a velocity loss of 182 fps and a TOF of .110895 (milliseconds)

Measured BC;  .517

The Palma rifle gave the following data;

Muzzle velocity;  2642 fps

Down range velocity at 285 ft;  2431 fps with a velocity loss of 211 fps and a TOF of .112519 (milliseconds)

Measured BC;  .448

The data from the 12" twist M70 is very consistent with arsenal published data for M118 SB ammunition for use in a 12" twist barrel.  The BC for the M118 174 gr FMJ M118 bullet is in the .485 to .500 range from a 10" twist barrel.  Arsenal testing back in the '50s demonstrated the 12" twist to give the best accuracy with the 147 - 174 gr bullets in the 7.62 NATO cartridge. 

What we see from the data is the 14" twist Palma rifle the TOF over the same distance was longer with a greater velocity loss resulting in a much lower BC.  The reason for the different measured BCs is because the M118 bullet stabilized fully in the 12" twist.  The M118 bullet was only marginally stabilized in the 14" twist rifle and therefore had more yaw,pitch and/or wobble thus it slowed down faster and since it was not as efficient moving through the air it gave a smaller BC.  The higher the BC of a given bullet at a given velocity the more stable it is.

My M43 PBL came with a 100 yard cable for the down range screens so that is what I use.  The TOF is measured from the muzzle screens to the down range screens which are in front of the 100 yard target. The actual distances are carefully measured and entered into the program. 

The M43 PBL measures a multitude of things concerning the internal ballistics as stated including the efficiency of the load.  The M43 also measured a lot of external ballistic data that is very useful.  While the Labradar gives a bit more data of the external ballistics it only gives, the same as any chronograph, a small picture of the internal ballistics.  A friend of mine has a Labradar and we are planning a side by side concurrent use it with the M43.  If it provides additional useful data I will probably get one to augment the M43.

LMG

 

Concealment is not cover.........

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dbarron posted this 08 February 2019

I bought a 35P in 2000, when it was a real budget strain.  Best investment I ever made.  It's still going strong.  I learned more about reloading in the first six months than from any other single thing I'd ever done.  That's still true.  I don't think that it's improved the accuracy of my loads a lot, but it's helped me to understand what's going on out there.  And also to figure out how to adjust a load that shot 1" groups in January and 2" groups in July.  Or vice versa. 

Don

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