Which chronograph is correct?

[LR338nut]

I posted the speeds of my 260 with 139scenars and H4350 last week. To me and everyone else they seemed slow, averaging 200fps below similar loads.

So, I went back to the range with my CED M2 and a friends Chrony. I loaded 20rds, 10 rounds each from different lots of H4350, and charge weight was 43.2gr. Then I fired 5rounds from each lot through both chronographs.

CED M2, AV MV for both lots about 2700fps
Chrony, AV MV for both lots about 2900fps

However the chrony had many ERRORS and only measured few rounds of the ten that were fired through it.

So, which one is correct? I want to believe the faster one, but it was the one that wasnt working correctly.

How can I test to find out if the chronographs are accurate?

 

[paulyosh]

Re: Which chronograph is correct?

Seems to me the two ways of verifying the numbers are:

1) Run something of known velocity for the conditions through both chronos
2) Take your load, and shoot it at distance, comparing your actual dope with computer-generated dope, which should give you some indication which is closer to correct (maybe neither)

The real question is, how did the load shoot? Is there a particular reason you're trying to hit a specific velocity? Real-world dope trumps all...

 

[vman]

Re: Which chronograph is correct?

Compare your figures to real life data.

Put both into a ballistics calculator and determine the drop. Fire some shots and see where abouts it is according to the tables. You may even find that both are wrong.

 

[Swan]

Re: Which chronograph is correct?

Know anyone with an Oehler? The Chrony seems closer, but doubt they are averaging 2900fps. But maybe. Your best bet is to shoot out to 600yds or so and record actual drop.

Then, send the M2 back to CED and have them replace it.

 

[Bloody_Tailgate]

Re: Which chronograph is correct?

Give a man a watch and he'll always know what time it is, give him two watches and he'll never know. Sometimes too much info is just that...too much information. Go out and test it like the others mentioned.

 

[427Cobra]

Re: Which chronograph is correct?

As long as your tightening the sensors to the bar with them slid on all the way, I would say your CED M2 was screwed up, call them and ask for a solution.

 

[LR338nut]

Re: Which chronograph is correct?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: vman</div><div class="ubbcode-body">Compare your figures to real life data.

Put both into a ballistics calculator and determine the drop. Fire some shots and see where abouts it is according to the tables. You may even find that both are wrong. </div></div>

So, does this mean that I might as well just shoot it at 1000, plug in the info into a ballistic computer and play with the velocity untill the computer matches my actual comeup?

 

[Rob01]

Re: Which chronograph is correct?

As long as your scope tracks correctly and the BC is right on the bullet then theoretically it should be able to tell you the velocity by reverse engineering it.

Just to give a little something similar to compare to, 43grns of H4350 in my 28" 6.5 Creedmoor with the 140 AMAX gives me 2870fps.

 

[vman]

Re: Which chronograph is correct?

LR338nut, spot on!

Wherever possible always try to match conditions on the day to the location that you are shooting.

Let the computer calculate the dope for you.

Let some rounds fly and see. As Rob01 has said, its reverse engineering. Its always recomended that shooters confirm their charts with real world data.

You wont need 1000 yards to determine this.

If you can, go to 400 yards with a tall target, say between 24-36 inches. Put a nice highly visible point of aim marker in the middle of the target. Aim at the same point of aim for all of your shots and see which of the drop charts (with their corresponding muzzle velocities) brings you closest to the point of aim.

If one is shooting below, and one is shooting above point of aim, this would indicate your muzzle velocity is somewhere between the two values.

If both are shooting higher than the point of aim, then your loaded rounds are both higher in MV.

If both are shooting low, then the MV's are slower.

 

[Enios]

Re: Which chronograph is correct?

We tried the same trick going from one chrony to the other and getting different speed. (Chrony Master and CDII) Then we lined them up in a straight line one behind the other and swapped them out... Instead of 100 to 150fps difference we got 20fps at the most.... If you have a load you trust and good on the trigger, we've found you will get a much better reading at the target with the chrony... ES & SD's will drop dramatically and you will find on most accounts, add about 25 fps to muzzle velocity and the ballistic programs are almost dead on when compared to 100yd speeds....

 

[Grump]

Re: Which chronograph is correct?

I would trust these comparisons a lot more if they had the 2-foot [or whatever] Chrony in the MIDDLE of the screens for the other one, using something like the 36-inch spacing I use.

You're talking a 7.4 percent boost in speed, comparing the faster with the slower. For 2-foot screen spacing, you would have to be off by a bit more than 1-3/4 inch to have THAT be the basis of difference.

Is your first screen at least 5 feet downrange??? Does the muzzle blast shake the diffusers a lot?