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Old July 9, 2019, 09:17 PM   #1
ReloadKy
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new to the chrony game

Ok so I just purchased my first chronograph. I want to know what I need to know about adding the use of a chronograph to my reloading / shooting. What kinds of SD's and ES should I be looking for? What should I take from being over / under published velocities in manuals? Any other info or suggestions would be appreciated.
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Old July 9, 2019, 09:58 PM   #2
insco3
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What kind of chronograph do you have?


I develop hand loads over a magnetospeed chronograph with great success.
I look for lowest SD and hone my loads around the lowest SD.

There are several ways to utilize the chrono to get the sweet spot in your load development. How are you currently planning to use your chrono to develop loads?
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Old July 9, 2019, 10:19 PM   #3
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There's no substitute for experience here. With time, you will create your own standards.

I chrono a lot of pistol rounds (you didn't state what you'll be chronographing). Low SD's are a good thing (of course). With lead wadcutters, using fast powders (38 Special), SD's typically run in the low-teens. But single digit SD's are rather common here. I have some loadings with SD's repeatedly running in the 5 to 7 range with 10-round samples.

Hotter ammo will tend to open up SD's. 38+P and 357 Mags tend to run in the high-teens, low 20's. SD's in the 30's are disappointing.

Semi autos tend to have higher SD's where the 20's are more or less normal. 45 ACP 200 LSWC's tend to have the lowest SD's; with single digit numbers occurring from time to time.

Basically: Heavy bullets and/or fast propellants tend to yield lower SD's. Lighter bullets and/or slow propellants tend to yield higher SD's.

For rifle, I've only chronographed 223 Rem for AR-15. And I haven't done a lot of it. SD's ran from 25 to 50, basically.

As for expected velocities: I don't pay a lot of attention. For starters, especially with revolvers (which I far and away shoot the most of), the load manual published velocities are through unrealistically long barrels. Or at least, barrel lengths much longer than those typically used. So the comparisons are apples n oranges. And I know about Ballistics by the Inch. But I'm not going to spend that much time on it. I have my data that I have accumulated over the years and I know what's right and what's not. As I said at the beginning of this: With time, you will create your own standards.
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Old July 9, 2019, 10:27 PM   #4
hounddawg
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what kind of shooting you plan on doing? Hunters use it to make sure the bullet will be traveling enough to expand and give humane kills at range. They also use it for drop tables to ensure the round they are shooting can stay within the kill zone. Pistol competitors will use it to make sure their loads will make power factor. For short range rifle shooters 500 yards or less it is just a fancy toy but even there a POI change of .1 or more can turn a nice group into a Wow ! group. Fir the mnost part though in short range it is nice to show off with but in real world any velocity variation will make little to no difference in the POI. Those shooting 600 yards and out look for powder nodes that consistent single digit SD's and ES's less than 20. Then they use the data to compute bullet drop. The longer the range the more velocity variation will have a impact on the POI.
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Old July 10, 2019, 02:23 AM   #5
std7mag
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I can't stress this enough, fresh batteries!!

When i'm doing a ladder test for a different powder/ bullet combo i leave the chrono at home. Not looking for fastest. My most accurate is what i'm looking for.
After i have my powder charge figured, i'll load up 10 rounds and shoot over chrono.
After i get my chrono speed i'll load somemore and shoot 600+ yards to true my ballistics.
I am always slower than max published loads.
The lower the ES/SD, the better.
But don't stress it too much unless you plan on shooting 600 yards or better.
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Old July 10, 2019, 05:06 AM   #6
ReloadKy
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I got a magneto speed sporter chronograph and will be shooting rifles of various calibers. My goal in reloading is to find hunting bullets that I can shoot MOA and also use the load for deer hunting. I also want to be able to do what hounddawg said and create my ballistics charts for shooting out to 200,300,400 yds. In my first test with the chrono I shoot three different groups with three different rifles. My 7 mag was 100 fps slower, my 30-06 was 60 fps slower and for some reason my 308 was 120fps faster than published by Nosler with the same powder and charge. Consequently my SD and ES were lower with the 308 as well.
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Old July 10, 2019, 07:08 AM   #7
fourbore
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I got a crony and expected it to be lot more useful. I can now satisfy my curiosity regarding muzzle velocity for reloads. If I plan to shoot the ammo, actually observing performance on paper tells me what I need to know.

I always wanted one, the prices came down and now I have it. It is not the valuable tool I expected. I know others get a lot more out of it and I hope you are one of those.
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Old July 10, 2019, 08:04 AM   #8
hounddawg
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When using a Magnetospeed realize that the point of impact (POI) will change slightly when the "bayonet" of the chrono is mounted on the rifle. No big deal just realize that it does shift slightly due to the effect on barrel harmonics
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Old July 10, 2019, 08:39 AM   #9
RKG
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Both SD and ES are expressed in units of FPS. As a result, the numerical values of different rounds will not be comparable.

A statistic known as Coefficient of Variability (CoVar) is computed by taking SD as a fraction of Mean velocity. As a ratio, it has no unit, and it allows direct comparison of different rounds, or, for that matter, different loads for the same round.

As a crude rule of thumb, if I develop a load who's CoVar is equal to or less than 1% (i.e., SD ÷ Mean ≤ .01), I generally consider the load adequately consistent and begin looking as other factors.
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Old July 10, 2019, 04:40 PM   #10
berettaprofessor
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Look up "Audette Ladder Test". That's the main use of a chrony in developing accurate loads.

The other uses of a chrony are about determining your reloads velocity to allow you to make accurate ballistic tables and predict the correction needed at various ranges.

Best advice; Shoot through the chrony at a target when testing loads ...helps avoid shooting your chrony.
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Old July 10, 2019, 05:25 PM   #11
hounddawg
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Quote:
Best advice; Shoot through the chrony at a target when testing loads ...helps avoid shooting your chrony.
funny but true. A kid at the LGS wsa telling me just recently how he had bought his first chrono, then promptly shot it the first time out. The OP is using a magnetospeed so no worries there as long as he uses the spacer installing it.

For rifles use a bore sighting tool https://www.pewpewtactical.com/best-laser-bore-sights/ I keep a small piece of foam board in the chronos storage box that fits between the uprights to make sure the tripod is set correctly. Saves time and chronos.

And the very best standard to use to measure the precision of your ammo/rifle/you combination is CEP or circular error probability which is a fancy way of saying "how does it group". If it can put 10 consecutive rounds into a one inch circle at 100 yards I figure it is a 1 MOA rifle
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Old July 10, 2019, 08:36 PM   #12
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Chrono is also good tool for anyone loading higher pressure rounds. Much higher velocity's than expected give some people cause for concern.
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Old July 11, 2019, 09:16 AM   #13
Bart B.
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I don't think a chrony is needed to develop accurate loads for use up to 500 yards for most rifles.

Your rifle and component lots are different than what published load data used. A 100 fps difference is normal.

Lowest SD and ES does not guarantee best accuracy.

If one is used, shoot at least 20 shots per load testing for accuracy at the same time.

Last edited by Bart B.; July 11, 2019 at 09:49 AM.
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Old July 12, 2019, 10:50 AM   #14
hounddawg
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I am getting ready to work up a hunting load for a 6.5 Grendel and will use the chrony to determine the maximum range I can use and still have the velocity for bullet expansion. Using the general rule of thumb that 1000 ft pounds of energy is good for medium sized game I know that 200 - 250 yards will be my maximum and I need 2400 - 2500 FPS out of the barrel to maintain proper velocity/energy for a humane kill. If I only can get 2300FPS my range would be limited to 150 yards. Most of my shots should be around 50 - 100 yards so all is good but a long range hunter needs to keep this info in mind
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Old July 12, 2019, 07:31 PM   #15
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I use mine to ensure my loads are safe and close to the velocity expected. MOST of the time when I work up loads the velocity I get is pretty close to what the load manuals predict. I'm not interested in hot rodding anything, but if I'm loading for a 30-06 I don't want 300 Savage velocities either.

I've ran into a few cases where velocity was much slower than I expected, and at least one case where my velocity was faster than expected even though the powder charge was well below book max. Without my chronograph I'd have been blissfully ignorant that my load was 100-150 fps slower than I thought in the former case, and overloaded in the latter case.

I'm a hunter 1st, who also likes to shoot at the range and at times go out to longer ranges than I'd normally hunt at. When hand loading I want to get all of the speed I can safely get with a book load that will be MOA for 3 shots out to 200 yards. Once I find a load that meets those goals I don't pursue things any farther. And much of the time I can exceed those goals by a little.

Without a chronograph I'd not feel comfortable going any farther than mid level loads that often are 150-200 fps slower than typical factory loads. With my chronograph I'm more comfortable working closer to max loads. In fact pretty much all of my loads are at, or very near the max listed in my load manuals. And my chronograph confirms that the speeds are where they should be.

I don't worry too much about SD or even extreme spreads. The groups on the targets tell me what I need to know. Perhaps for extreme long range shooting it might need more attention.

Knowing the actual MV is helpful to predict bullet drops along with one of the online ballistics programs. But at typical hunting ranges that isn't a huge deal and is really secondary for me.
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Old July 13, 2019, 08:58 AM   #16
Bart B.
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I have seen a 50 fps average spread across 3 people shooting the same rifle and ammo. We didn't hold the rifle against our shoulder the same way.
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Old July 13, 2019, 03:36 PM   #17
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Quote:
Originally Posted by beretta professor
Best advice; Shoot through the chrony at a target when testing loads ...helps avoid shooting your chrony.
Not with the Magnetospeed. It's attached to the barrel. On the plus side, you can't shoot it. On the minus side, it affects point of impact so you can't shoot for group size with it on the gun, as it changes that. You have to do the two separately.

Quote:
Originally Posted by jmr40
I use mine to ensure my loads are safe and close to the velocity expected.
There are several reasons most chronograph manuals tell you not to base your load workup on these instruments other than in side-by-side comparisons. One is many instruments are off by a bit. I have seen up to 200 fps disagreement in optical chronographs when the light wasn't great.

Another is that even if the chronograph is accurate (and the Magnetospeed should be) if you have a gun with the same barrel length as the published data was developed with and that shoots a load slower than the load data shows, you are safe working up to a matching velocity if load to ensure the powder is back over the flash hole at firing. If your barrel is shorter, you will be over the book pressure when you get to that velocity. If your gun has the same barrel length as the data gun, but shoots faster than the published data, as the OP's .308 does, then you likely have a tighter bore than the standard test barrel does and when it matches the velocity of the standard test barrel, it will actually be running at higher peak pressure than the test gun did. Most standard rifle test barrels are 24" long, so if yours is longer higher velocity is to be expected.

As Bart points out, how you shoulder the gun affects velocity enough to question your chronograph's match to published load data. I can only suggest you pull the stock hard into your shoulder, keeping in mind the test gun was in a fixture.

An additional thing to keep in mind is the powder position in the case. I have seen 30-06 NM shoot 80 fps slower when the powder is forward in the case than when it is back against the flash hole. The SAAMI procedure has the ballistic technician handle the cartridge so the powder is back over the primer (maximum pressure and velocity produced) when it is fired.
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