Chrony use


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armoredman
January 1, 2007, 11:15 AM
I have a Chrony F-1 I bought some time ago, and used once, promptly blowing one ofthe sky screens right off...:o Oops.Well, I got replacement sky screen wires, but shelved the unit in favor of making the most accurate loads I could.
Well, now I would like to chronograph my rifle loads, but I was wondering how far in front of the muzzle i should put the unit? I am testing 7.62x39mm, 7.62x54R, and .303 Brit.

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model 649
January 1, 2007, 11:34 AM
Ahh, yes, shootin' the chrony! Know it well. you can put it out 8-10 feet. The best way to avoid hitting the instrument by using a target beyond it to aim at, instead of trying to shoot "just above" the screens.
Josh

The Bushmaster
January 1, 2007, 11:45 AM
And remember, if you are using a scope on that rifle. Make sure that you shoot high enough over the sensors that the bullet will pass over them. Or you will hit the sensors....:what:

armoredman
January 1, 2007, 11:48 AM
No scopes, my milsurps are "stock".:cool: Thanks, guys.

Thirties
January 1, 2007, 11:55 AM
With my chronometer, I tape a piece of corrugated cardboard to the outside of the furthest sky screen, and place a red dot on it, or a circle with a sharpie pen.

I shoot at that bullseye for my readings. Since I started that method, I've never had a "mishap".

Forget trying to line up the chrono at 8feet with a target at 10 or more yards. Too much fiddling and time trying to line everything up, plus too easy to shoot the thing that way.

The Bushmaster
January 1, 2007, 11:58 AM
Just thought I'd mention that. I notched one of my sensors with my .30-06.

If you get irratic readings at 8 to 10 feet. Just move it out 2 feet until they settle down. I can shoot my .30-30 at 8 feet, but I have to have my chronograph at 12 feet for the .30-06. Mine can see the muzzle blast and sometimes will knock it over.:banghead:

Hummm...May have to look into that, Mr. Thirties...Thanks.

clown714
January 1, 2007, 07:53 PM
I have had no problems at 6'.


I keep a tape in my chrono bag just for that purpose.


biggest round I load for is '06.

clown

sctman800
January 1, 2007, 08:28 PM
It depends on what you are shooting, if you get wierd readings you are probably too close for that gun. I can sit the crony close while checking .38spl or .45ACP then I must move back for .41mag or 454Casull.
I also pick out a target to aim at past the crony and havent hit it yet. Jim.

MCgunner
January 1, 2007, 10:03 PM
I bought a chrony from Gander Mountain when I first saw 'em 20 odd years ago. I started using it with my handguns and rifles. First, I worked up a load I'd read about for my ol' reliable .257 Roberts, worked out fantastic. I later got a 7mm Mauser, shot .243s, .270s, a .300 Savage over it. I always set it 10 feet from the muzzle.

Then, I got a 7mm Remington Magnum. I worked my first loads up, mild for the caliber, working up pressure. I set the chrony out at 10 feet, fired the first shot and the muzzle blast blew the unit on the tripod over. :evil: :evil: :evil: ROFL! WOW, MAGNUM BABY!:D

So, I backed the thing out another 5 feet and it worked better, blew a screen off occasionally, but the unit stayed upright.:D Yeah, I always line it up with the target and shoot for group size at the same time I'm taking chronograph readings. I've had the thing 20 years and it still works fine. I bought new screens for it a while back. The original were cardboard and they were gettin' pretty sad lookin' all taped up with duct tape. The old screen has a small shooting area and it's marked for scope hold or iron sights on the front. They used to do a deal where you could send it in and have it converted to the new screens with the sticks, but I never got around to it and now they don't do that anymore. :banghead:

SlamFire1
January 1, 2007, 11:14 PM
I have a Chrono Chronograph, been using it for years now.

A chronograph provides useful data but is not to be trusted implicitly. There are things such as instrumentation error. I believe this is due to misalignment. When you consider the short distance between the sensors, around 12 inches, and velocity is calculated based on the time it takes the bullet to cross that distance, the tiniest variation in that distance caused by off axis misalignment will create differences in reported velocities. I have found over the years that values can vary day to day. Velocity averages will never be exact, but I believe they are comparable as long as they are within the Standard Deviation of a previous session,. I believe that you should start off a chronograph session with a “calibration load”. For me this load is something that I have fired before and have confidence in the velocity numbers.

I stick it on a cheap camera tripod that I purchased from Walmart. I level my chronograph using a cheap Laser Level purchased for under ten bucks at Harbor Freight Tools. http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=54050. I use this to level the Chronograph and use the laser to orientate the center line of the chronograph on my bench rest. I believe this reduces my misalignment error. I have noticed the slightest bump or movement in the chronograph will give radically different velocity readings.

Sometimes powder chunks going over the sensors create warp speed readings and the only cure is to move the chronograph further out from the muzzle. I do not think it makes any real difference on indicated velocities. Black powder rifles blow out so much unburnt chunks of powder, that I have had to put my Chrono out maybe 30 feet away or I get display errors. I have a M1911 Swiss that with its long barrel and slow burning powders require the chronograph to be placed out further than normal or the screens get blown off..

Acceptable velocities depends on the loads and the rifles. You will find some barrels are faster than others. And as you pop primers in the fast barrels, you will figure out the thresholds for that firearm.

What about those funny numbers , Standard Deviations and Extreme Spreads? The Standard Deviation and Extreme Spread numbers are not as important as what your group looks like on paper. But for those who want a standard, assuming already outstanding on paper performance, I am going to give you some impossible criteria. I asked the gunsmith who barrels my Match Bolt Rifles, this man is Nationally ranked Highpower Competitor, last couple years was in the upper ten, has won the Long Range Aggregate and I think Wimbleton, about his criteria. He wants a long range load that has a SD less than 10 and a ES less than 20. Of all my loads that I have chronographed, and there are many, I have had two or three that met this criteria. But there is a standard for you to shoot at. Pun intended.

The chronograph is a tool, useful for checking velocities. Consistent ammunition is always good, means you have your reloading processes down. But the numbers do not guarantee accuracy. You will find that errors in position, errors due to wind changes, errors due to flinching, are typically larger than your ammunition errors. But it is worth making good enough ammunition that you can concentrate on fixing the other things.

USSR
January 2, 2007, 09:22 AM
armoredman,

A MINIMUM of 10 feet, but 12 - 15 feet is better. Having used a chrony for several years, I will say that one thing that will give you false high readings is bright, direct sunlight on your sensors. If you are shooting on a sunny day, depending on the angle of the sun, you will need to provide some shade for the sensors to get accurate readings. Here is what I do:

Install the diffusers, and then tape a translucent material such as paper between the two diffusers, making sure to have the material overlap the diffusers on all sides.

This will take care of the false high readings you will get in direct sunlight.

Don

armoredman
January 2, 2007, 10:25 AM
Thanks for all the replies, I appreciate it!:)

Walkalong
January 2, 2007, 10:45 AM
Ditto on the chrono only being good for just so much. They are usefull, but can't do it all. The best numbers don't always shoot the best. On target is the final say in the matter.
I have never chronoed a benchrest load, nor have I ever wieghed a charge for it. X.X number of clicks of H322, N133, or Tac. Usually N133. Tac is finicky in humidity, but can shoot some great groups. :)

I've shot two rods on my chrono. Not too close (5 steps), just careless shooting.

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