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Old July 15, 2011, 01:04 PM   #1
UtopiaTexasG19
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Chronograph Set Up On Home Loads....

I just received a small simple Chrony Chronograph and used it for the first time with some .38 special re-loads I just finished. All of these .38's were carefully prepared and I used a electronic weigh scale to get the powder at the same grains down to the same tenth of a grain but the results from the chronograph show some large variations in feet per second after shooting the rounds. In 25 rounds the fps ranged from 960-1209 with the vast majority around 975 feet per second. Are my re-loads that different, am I setting up the chronograph wrong, or are these cheaper chronographs that innacurate? I really don't know what I expected! Any tips would be appreciated...
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Old July 15, 2011, 01:28 PM   #2
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How far was the chronograph from your muzzle?
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Old July 15, 2011, 01:44 PM   #3
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UTG19, thats a pretty big difference. I use the same Shooting Chrony and have been happy so far[about six years] Check your distance to chrony like dmazur said. I usually put it out at 12' for pistols. What gr bullet were you testing? And what charge of powder? Barrel length? These all come in to play. Make sure your screens are on if its sunny. Also, try putting a piece of Scotch tape over both of those little windows on each end of chrony. It will help.
Let us know how this works out.
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Old July 15, 2011, 01:49 PM   #4
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You'd be surprised what affects the speed of a bullet. Especially in a revolver round like the .38 special. Crimp is one big factor, along with cylinder gap. A chronograph can tell you more than speed, and sometimes the other things are more important, like extreme spread and standard deviation. If your Sd is small, then load is generally more accurate. If the Es is small then the load is generally more accurate.

So, if you saw velocities from 960-1209, we know that your extreme spread was pretty harsh. But, how was your standard deviation?

How far was your chrony from the muzzle. If you're too close, some of what you're measuring might be muzzle blast.
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Old July 15, 2011, 02:26 PM   #5
UtopiaTexasG19
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I loaded these light with 110 grain bullets and 4.6 grains of HP-38 which the charts show as a beginning load. All the casings were cleaned, sized, flared, primed, loaded with powder, bullets seated and crimped at the same time so deviation I assume is not from that aspect but who knows? From the posts so far I gather I was way too close to the chronograph at 3.5 feet and muzzle blast is probably the problem. I was afraid I might shoot the chronograph at a longer distance! I'll try some more rounds this weekend with the chronograph further away. Hopefully I won't wound it in the process!!!
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Old July 15, 2011, 03:38 PM   #6
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Thank you for the information. You were all right in that I had the chronograph too close to the shooting bench. I moved it out about 12 feet and tried out some 30-30 Winchester loads I worked up this last week and the FPS were all very close. Thanks!!!
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Old July 15, 2011, 03:41 PM   #7
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I had the same problem with a different brand of chronograph, one that was known accurate with rifle loads. In my case it was muzzle blast & sonic wave at right about mach 1.

The cure for me was a cut piece of cardboard about 12" in front of the START screen with a 2" hole in it to allow the bullet through but to trap & disperse muzzle blast. I just cut pieces out of a box & built a Bubba gizmo with duck tape.

That dropped the errors to 25 FPS without anything else being done. Give it a try & see how it works for you.
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Old July 16, 2011, 09:58 AM   #8
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If you get to close to the sensors you will read the speed of sound from the muzzle blast.
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Old July 16, 2011, 01:15 PM   #9
Kevin Rohrer
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I guess I need to ask the obvious question: How far away should a rifle and pistol be from the start screen to get an accurate reading?

And a second question: Should the diffusers be used in bright sunlight but not during overecast days?
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Old July 16, 2011, 01:42 PM   #10
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15 feet is usually good enough.

When you read 1100 to 1200 ft/s on a 230 grain, .45 ACP, ball load you know something is wrong.
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Old July 16, 2011, 02:11 PM   #11
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15 feet has become a standard used in a lot of manuals and also magazine articles. One fellow on the board said his .338 Lapua magnum needed 18 feet before readings settled. A lot of folks fire pistol as close as six feet, but I wonder about some of their readings and think 10 ft is a better minimum for handguns. I use 15 for both rifle and pistol just to be consistent.

For .38 Special barrel length is also an issue. A lot of the snubbies seem to have pretty wide velocity spread, but once you get to 3" and longer, it's not normally a big problem.

The CED chronograph page has a good list of factors that can go wrong in chronograph readings when you pull the scroll bar about half way down, under "Variables that will affect results. . ." Some of it just applies to their machine, but most apply to all. They state that chronographs can disagree by as much as 8%.

CED's unit gets high marks for accuracy, as does the Oehler. For others you need something to compare to. .22 LR Match ammunition is usually within 50 fps of the claimed velocity. The standard velocity barrel length is 24", but the bullets cease accelerating somewhere in the range of 19", so velocity doesn't change a lot between there and 24". Anything between 18" and 24" should be close.
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Old July 16, 2011, 02:11 PM   #12
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I keep my chronograph screens 20' from the muzzle. Even that far out, some of my rifles blast it a bit (30-378, 378, 45-120 NE, and 50BMG).

The easiest set up for your chrony is to get a cheap camera tripod that has the detachable camera mount for it. Make sure you get one that will stand high enough! Then attach the mount to the bottom of your chrony "box". Set up and take down is quick that way and your screen and box will fit back into the original container without a problem. As for the tripod, I keep it in a nylon bag that belonged to a camping chair that broke (cheap walmart). Note to self: look for small nylon bag to put chrony in.
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Old July 16, 2011, 08:33 PM   #13
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I think most of the people that shoot their Cronys , don't have them on a Tripod ! No Tripod makes proper adjustment difficult ! I guess if you use a Crony very much , sooner or later you are going to tag it with a bullet . I read a piece of advice recently that said to use bamboo Bar B Q skewers to attach your Sky Screens . The fellow said you can shoot them and they just splinter and disappear without slamming the whole business on the ground . Makes sence to me !
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Old July 20, 2011, 01:39 AM   #14
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Instead of a nylon bog for my Chrony I bought one of the portable office file plastic boxes. I tad bulkier but room for spare batteries, Chrony printer and pater, target accessories and is basically waterproof. Next is to see if there is an affordable tripod that will fit in the same box.
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Old July 20, 2011, 06:22 AM   #15
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I use 12ft.
I use (okay, I used to, when I was still 'learning') a target behind the screens for an aim point.
I test the same-lot ammo at different times of the day, and on different days.
I use control ammo at step-up.

Granted, I need only take ten steps from my bench to go shoot.....
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Old July 20, 2011, 09:41 AM   #16
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I still use a point of aim of some kind. Usually a target so I can get a group and velocities at the same time. The main thing I do that only a few others have caught onto that I am aware of, is to set the gun on bags so it is on the point of aim, then put a laser sighter in the bore. I then adjust the chronograph screens until the palm of my hand finds the red spot in the middle of both the front and rear screens. That way I don't have to go back and forth between the instrument and the bench several times to get the right alignment.
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Old July 20, 2011, 05:11 PM   #17
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I had a problem with a Chrony F1 I purchased from Wal-Mart. A little different then your issue, mainly I was getting E1 errors but I did see some wild extreme spread issues and wildly unrealistic velocity readings as well. After a bunch of great help here failed to solve the issue I sent the unit to Chrony. The report back said the unit was "found to be too sensitive" and a replacement was sent back. The replacement works much much better. A couple of weeks ago I ran about a hundred rounds over it at about 15 ft, everything from .270 win at 3000 fps to 45 acp and 38 special DEWC at 770 fps. I think I had 3 errors and none of my various loads, commercial and reloads, had extreme spreads over about 50-60 fps.
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Old July 21, 2011, 10:04 AM   #18
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That's one thing I like about the CED M2 design. It's the only one I know of that adjusts its sensitivity to the ambient light conditions automatically.
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Old July 21, 2011, 10:34 AM   #19
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Shoot the ammo at 50 yards, that will tell you more about the ammo then a chronograph will.

They are handy, but don't really tell you about accuracy.
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Old July 21, 2011, 10:52 AM   #20
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Yes Sir MR. Kraigwy, I feel the same way!!! A good componenet to have even though I've never owned one but accuracy is my goal.
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Old July 21, 2011, 12:27 PM   #21
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Not your first purchase to be made, but very handy. One thing I've used mine for repeatedly is to get a velocity match to prior lots loaded with the same name components, but different lot numbers. This saves time over running a whole new ladder or round robin, and can usually be done in 10 shots. Accuracy still needs to be verified, but this greatly narrows the range of possible adjustments needed.
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Old July 21, 2011, 04:33 PM   #22
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I use 12 ft from the muzzle and use a target behind the second screen with a red dot for aiming. Haven't shot my Ohler yet.
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Old July 22, 2011, 06:47 AM   #23
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I probably should have mentioned why 15 feet is common in published load data. It is the average distance between screens specified by SAAMI for standard velocity measurements. When you see a velocity published for a commercial round of ammunition, for example, it will have been fired from a SAAMI specified velocity barrel, which has a minimum chamber, same as a pressure barrel, and a specified length (see below). Indeed, SAAMI specs allow pressure barrels to be used for velocity testing.


Centerfire Rifle Standard Velocity Barrel Lengths from 1992:

.22 Hornet — 16.000" ±0.010"
.30 Carbine — 20.000" ±0.010"
7.62x39 — 20.000" ±0.010"
350 Rem. Magnum — 20.000" ±0.010"
351 Winchester — 20.000" ±0.010"
44 Rem Mag — 20.000" ±0.010" (rifle only)

All others: 24.000" ±0.010"
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