Chronograph . . . Uses for

M

Montana Pete

Guest
I have recently ordered a chronograph, which should arrive any day.

I was wondering if folks could suggest the uses/benefits of the chronograph.

One benefit that occurred to me would be to assess the consistency of ammunition. That is, the variation in velocity shot-per-shot.

Other uses suggest themselves . . . . . .

One wag wrote on a forum recently that he was sad to see the "hot air" coming out of many ammo claims. Using his chronograph, he found that actual velocities of loads were as much as 250 fps less than claimed. This might apply to factory ammo claims, as well as claims in reloading manuals.

Also . . . . there's been great "hot air" on the forums, esp. the hunter-type forums, about very short barrels, such as 20 inch barrels. Seems like these debates could be settled, if two rifles were obtained, one with a 24 or 26 in. barrel, and one with a "chopped" barrel. Frankly, I have difficulty believing the "don't make no difference" camp. I see statistics on the internet that some cartridges, such as the .270 Winchester, show a very significant loss of velocity in short barrels, whereas other calibers such as the .308 do not show nearly the velocity reduction. So . . . "it depends."

Any comments would be welcome--
 
The best way to tell would be with one rifle with a 24"-26" barrel. Shorten that one rifle barrel one inch and re crown at a time taking measurements with the chronograph at each one inch step. Use the same load for each step. What you will find is a approx a 25fps reduction per inch down to the shortest of 16' barrel reduction.


If it didn't matter with a .308 Winchester you would see a lot of 16" barrels on .308 Winchester chambered for this ctg.

But what the hey, prove it for yourself.:D
 
IMO the powder used makes a big difference in the short vs long barrel debate. Until you get to the super slow burners there often is very little to none difference in the velocity of some cartridges.

I clocked these 7-08 Rem loads with a Pact M1 from a Remington M7/20" BBL and a M700/24" bbl, and got these figures.

140gr Nosler Partition - 45gr IMR4350/Rem 9.5 primer
M7 = 2528fps
M700 = 2540fps

140 gr Sierra SP - 45gr H414/Rem 9.5 primer
M7 = 2566fps
M700 = 2578fps

Federal Hi Energy 140gr TBBC
M7 = 2720fps
M700 = 2845fps

Hornady Lite Mag 139gr Inter-Loct
M7 = 2724fps
M700 = 2890fps

I`m sure the chamber, bore and throat variations have some effect on the velocity. I can`t measure these though and have found the 260 rem to react similar to differences in BBL lgt. Personal opinion is there is likely about 20 fps max per inch difference in 308 based cartridges as to what you can expect from the same load in two barrels of different lenght.
Again JMO
 
Montana

I use my Chrono every time I shoot and find out a lot regarding what is going on. I also set up the chrono exactly the same distance from the muzzel.
I suggest you get a small thermometer to take with your chrono.
and don't change thermometers.
When you start a test you will get the velocities but you will also get the extreme spread and the standard deviation.
The extreme spread is the highest velocity vs the lowest.
The SD for me is how well I loaded the cartridge. The lower the better.
Let's say a SD of 10 is good so a 6 SD would be better but a 45 SD is poor.

Now the numbers you will get will be your numbers. This is important as you are not buying a Certified Chrono so the numbers will be good within parameters.

Keep track of the temperature as you test as you should see velocities go up as the temperature gets hotter and lower as it gets colder.

If your shooting matches you will want to keep your best group velocity marked down so you can try to achieve it at all different temperatures.
The fun never stops with a chrono. :)
Centerfire
 
Montana Pete

I had bought a chronograph a few years ago for the same reasons. To make my loads more consistent and see if the chrono could show why some shots would fly out of the group. The only time I get it out now is to see how fast a good load is going.

I only shoot paper at 100yds, and undoubtably those who shoot farther than that will have different results than I did. I couldnt find any correlation between variation in velocity (SD) and how well a load grouped. One load in my .223 shot .270 for 3 shots at 100yds with IMR4198, with a SD of 112fps! There are other loads this rifle shoots with a SD of less than 15 that dont group at all. There are also some loads that everything works right.

I use the target for load development because the chrono didnt really answer anything for me, and raised alot of questions on its own.

If you shoot between 600-1000yds, you will get more use from the velocity data than I did shooting at short range.
 
I use my chrony to adjust my loads back to the right velocity when I change powder lots, sometimes one lot to the next you'll find a BIG speed difference,,,

the wind is my friend,,,,,,,,,,,,,,,

DD
 
What's a chrono good for you say? :confused:
Well, lessee:
velocity uniformity, pressure curves, temperature effects on powder, primer effects, neck tension effects, burn rates, lot to lot variations of powder, establishing maximum pressure for your rifle, prediction of max pressure, clean barrel shot velocities, load ladder testing, testing velocity for drop chart creations, hot ammo/cold ammo testing, node window calculations, brass strength comparisons with equal pressure loads, barrel length vs. velocity loss, mapping out loads for matches in advance, dispelling bogus factory ammo speed claims, dispelling bogus buddy's miracle load claims, and if you have TWO chronographs, you can test ballistic coefficients!

Yup, they are handy tools!:eek::D
 
Thanks for the information. Here's the results of my first day with my new chronograph. Comments welcome. Chronograph was the Chrony Alpha model -- a very inexpensive little device.

==============
June 24

I shot three batches of 22-250 ammunition. All used the 55 grain Hornady flat-base, spire point bullet. The only variable was the powder charge.

Here are the results--

Batch #1 -- 30.0 grains of IMR 3031 --

3576 fps
3567
3558
3586
3570


Batch #2 -- 30.2 grains of IMR 3031 --

3594
3586
3585
3584
3586

Batch #3 -- 31.5 grains of IMR 3031

3648
3660
3682
3696
3675

Comments:

Even though the first two batches of ammo are only separated by a miniscule 0.2 grain of powder, the chronograph appears to have picked up this difference. There's a slight but detectable velocity difference between batches 1 and 2. The consistency of batch #2 is rather surprising, and suggests this may be a good target load.

As for the three bullsye targets used -- each with 5 holes -- the first and second batches produced pretty good targets, but the third was not so good. I noticed that the velocity variation is much more pronounced with the third batch. Batch #2 looks like a good bet to reload.

The velocity was a pleasant surprise. the numbers were a little higher than I might have expected for mild loads, but I was shooting a 26 inch barrel, and on a very hot day.

I did not shoot more because it took me about 20 minutes to set up the chronograph-- never having done it before. So that wasted time, plus the high temperatures, sent me running home to the air conditioning. It was darn hot out there.
 
Thanks for posting, it is good to see real world use of a chronograph and how just a small change can show up. Been considering the purchase at some point, leads me to think it might be a wise investment at some point.

Hot, heck yeah it's dang Hot here (N.Tx)..have some fresh loads to take out this weekend (early) before the heat really sets in.
 
one other use

one must know the FPS of a load thru your gun to make a drop chart for hunting. then if you know the exact yardage to taget and angle and speed of wind. one can have a pretty good chance of hitting the intended target the first shot. Fred
 
Don't forget about the average and standard deviation (s.d.) numbers. They let you know whether the differences you see are likely real, or just a result of the natural random variation from one shot to the next.

For example, from your numbers I get:

Batch #1 -- 3571 +/- 10 fps (+/- 0.29%)
Batch #2 -- 3587 +/- 4 fps (+/- 0.11%)
Batch #3 -- 3672 +/- 19 fps (+/- 0.51%)

The +/- numbers are the s.d. and the numbers in parentheses are the s.d. as a percentage of the average.

As a general rule, if two averages differ by more than their s.d.'s then the difference is probably real, otherwise the differences might just be because of random variations.

Also, it might be useful to know that as long as all other conditions are practically the same, the s.d. lets you make predictions about the future variation in velocity. 68% of the time the velocity should be within 1 s.d. of the average, and 95% of the time it should be within 2 s.d. of the average. So for example, 68% of shots with batch #1 should have velocities between 3561 and 3581 fps, and 95% between 3551 and 3591 fps. This all assumes that you have enough shots for the average and s.d. to actually be representative.

s.d. as a percentage is a good way to see the relative consistency in velocity. A 10 fps variation in velocity is relatively more important at 2500 fps than at 3500 fps.

If you want to see a relation between velocity s.d. and group size then unless the differences are pretty large, you generally have to use something other than c-t-c to measure group size because its pretty sensitive to the random variation in individual shot placement in the group.

Sorry if that's too much detail, just thought it couldn't hurt.
 
Last edited by a moderator:
Montana Pete said:
Thanks for the information. Here's the results of my first day with my new chronograph. Comments welcome. Chronograph was the Chrony Alpha model -- a very inexpensive little device.

==============
June 24

I shot three batches of 22-250 ammunition. All used the 55 grain Hornady flat-base, spire point bullet. The only variable was the powder charge.

Here are the results--

Batch #1 -- 30.0 grains of IMR 3031 --

3576 fps
3567
3558
3586
3570


Batch #2 -- 30.2 grains of IMR 3031 --

3594
3586
3585
3584
3586

Batch #3 -- 31.5 grains of IMR 3031

3648
3660
3682
3696
3675

Comments:

Even though the first two batches of ammo are only separated by a miniscule 0.2 grain of powder, the chronograph appears to have picked up this difference. There's a slight but detectable velocity difference between batches 1 and 2. The consistency of batch #2 is rather surprising, and suggests this may be a good target load.

As for the three bullsye targets used -- each with 5 holes -- the first and second batches produced pretty good targets, but the third was not so good. I noticed that the velocity variation is much more pronounced with the third batch. Batch #2 looks like a good bet to reload.

The velocity was a pleasant surprise. the numbers were a little higher than I might have expected for mild loads, but I was shooting a 26 inch barrel, and on a very hot day.

I did not shoot more because it took me about 20 minutes to set up the chronograph-- never having done it before. So that wasted time, plus the high temperatures, sent me running home to the air conditioning. It was darn hot out there.
Click to expand...


I'm gonna let you in on a little not so secret-secret that some don't know about. You mention that the chrono picked up on the .2 grain change...that's nice to see but what you want to look for as you go up in powder...is when you dont get a change. You'll see that normally for about .5 to 1.0 grain depending on case, etc. When you see that, go back to the middle and fine tune you accuracy....the tune will stay longer throughout the day.

Hovis
 
montana

i tried 3031 imr in my 22-250 at first too. the one my rifle liked was varget. and like you found with the 3031 no full house loads! usually 1 -1.5 gr below max shot clover leafs.
also h380 but that is a ball powder and sensitive to heat. which is not a factor around here hunting chucks as on a good day i may see 10 chucks but they are so spooked i only get shooting at 3-5 of them so i am basically shooting a cold gun.
just a suggestion as my first 22-250 was a wickliffe single shot and the bullet it liked was the sierra 53 match with 3031! really accurate but not ethical for g-hogs. my first one crawed to its hole. from then on i shot 55gr sierra blitzkings with varget and have enjoyed many one shot harvests.
Fred
 
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