Is my (new) chrony wrong?

legi0n

legi0n

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Many moons after my first chrony died of a gunshot wound :) I got a new one. A beta. First trip to the range and a kid shot out a diffuser rod but that's another story.

So, before getting it shot again I tested some of my 30-06 loads.
180gr Hornady Interlock over 52.3gr H4350 gave me an average of 2649fps with a standard deviation of only 2.38!

The ballistic charts for this bullet at this speed and 40°F say the 200yds drop is less than 5" when zeroed at 100.

Well, my real bullet drop @200 is about 7"!!!
This could only happen if the muzzle velocity is about 2222fps.

Is something wrong with my chrony? I did open it fully....
 
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Could be yards to meters mix - up - but I doubt it at 200 as 20 yards SHOULDN'T make 2" drop difference....zero at 100 and go out to 400 or 500 and measure drop....that'd be more accurate.

There's no calibration standard or requirement on Chrony's - could be out - I found myself with my chrony and two other chrony's at the gun range in the summer - three chrony's one gun - no chrony measure the same velocity as the other with my 223, but each chrony did display very similar SD. At best I think Chrony "gives you an idea" where to start, but nothing like shooting the distances you expect to shoot in the field tells the true story.
 
check this out, my crony sais my 300winmag is doing 3495fps with 79g of rl 22 and a 165g interbond! HOLY CRAP! during the season this was O.K. as the rifle seemed to handle it. however in the summer, bolt lift was sticky and primers cratered. primers seem to crater all the time on various rifles i have owned but bolt lift sticky? plus accuracy suffered. i backed off the charge to 77g and am still getting over 3300 fps with no functional problems. so is the chrony accurate? i would say it seems to be pretty close. the rifle by the way is a Rem700/spsdm with a 26" barrel.
 
I am also leery of my chrony. Yesterday (acording to the chrony) I was pushing 130 gr. Bullets out of a .308 win (Stevens 200) at 3300 fps !!! . Just checked my notes..that was pushed by 44 gr. of 4064 .
 
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44Bore said:
If my memory is corrrect the bullet drop is also affected by the height of the scope over the bore in terms of where it will actually hit.
Click to expand...

I agree but must add that barrel length, bore and groove diameters also play a big part as well as bullet type and ballistic coefficient, temp and air density.
 
maynard said:
I agree but must add that barrel length, bore and groove diameters also play a big part as well as bullet type and ballistic coefficient, temp and air density.
Click to expand...

Can you not eliminate barrel length, bore and groove diameter from the equation when you know the measured velocity?
 
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I trust my Chrony. It almost always reads close to what I expect and if it doesn't I can usually find a reason with my loads. Finding the unexpected variations is one of the reasons I use a chronograph.

I once tested my Chrony by placing in back to back with an expensive Oehler chronograph and shooting thru both of them. Then I reversed them and did it again. In both cases the the chronograph that was a few feet downrange from the one closest to the bench read a couple fps slower than the closer one. So, in other words, he results were identical.
 
762shooter said:
I trust my Chrony. It almost always reads close to what I expect and if it doesn't I can usually find a reason with my loads. Finding the unexpected variations is one of the reasons I use a chronograph.

I once tested my Chrony by placing in back to back with an expensive Oehler chronograph and shooting thru both of them. Then I reversed them and did it again. In both cases the the chronograph that was a few feet downrange from the one closest to the bench read a couple fps slower than the closer one. So, in other words, he results were identical.
Click to expand...

It's not that I don't trust mine. Just that the practical bullet drop is way higher than calculated.
And for a hunter the sub-MOA group size is less important than predictable bullet drop.
 
762shooter said:
I trust my Chrony. It almost always reads close to what I expect and if it doesn't I can usually find a reason with my loads. Finding the unexpected variations is one of the reasons I use a chronograph.

I once tested my Chrony by placing in back to back with an expensive Oehler chronograph and shooting thru both of them. Then I reversed them and did it again. In both cases the the chronograph that was a few feet downrange from the one closest to the bench read a couple fps slower than the closer one. So, in other words, he results were identical.
Click to expand...

Pretty lucky to get that close, because the chronographs I see advertise as being accurate to 1%. That's 26 to 30 or so fps variance to be the built in tolerance.
 
Grizzlypeg said:
Can you not eliminate barrel length, bore and groove diameter from the equation when you know the measured velocity?
Click to expand...

Yes if you know the measured velocity. But if you were jusy going by published book velocities ie. X amount of powder with Y bullet gives you Z velocity, the bullet drop could be very different from the book.
 
The photo sensors in a Chrony look straight up. One starts the clock and the second one stops the clock. It "knows" the distance between the two sensors, so can calculate the speed.

if the Chrony is not quite folded all the way open, the sensors will be looking slightly towards each other, reducing the actuial distance, thus stopping the clock a bit sooner than it should. This is the usual cause of a "fast" Chrony.

The test of a Chrony is a 22 rifle with some decent ammo. It should produce a velocity within 50 fps of the advertised speed.

Or, fire a few rounds of factory ammo. If it is 500fps fast, you know you have a problem.
 
A quote: "Or, fire a few rounds of factory ammo. If it is 500fps fast, you know you have a problem."

If it reads 200fps slower than the factory is advertised, the chrony is likley very close!
 
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