Chrony help, i have to be doing it wrong

N

nwt2002

CGN Regular
EE Expired
Rating - 100%
20   0   0
Location
Calgary
okay first off i havent shot my chrony... good start.
I bought it a couple years ago but it finally made it out of the box yesterday, i was testing some loads for my 300 win mag, however the bullets where fast really really fast.

the load: 300 win mag, barnes 168ttsx, imr 4831 72.0 -73.0, cci mag primers

the loads started around 3300 fps and ended around 3500 at 72.8.

the book says it should be around 3100 ish.. okay id love to have bullets shoot that fast... but somthing aint right.

fired brass look good, nothing obvious for over pressure. ..

any ideas.
thanks
 
Also, make sure the chrony is far enough away from the muzzle to avoid muzzle-blast which will give bad readings.
 
200- 400 fps too fast-- or faster than the data calls for

That is a tough one if it was 100 fps i wold say sure and back off a tad

If it was more I would say too close to Muzzle

How close was muzzle to chrony 10-12 ft or more 15 ft

it is a possiblility depending on different componets

How did the loads group ??????

I am on the play it safe side of the coin and I would reduce loads!

One way to check is to save a few Factory rounds to check
 
to answer a few of the questions, not a custom rifle, rem 700, 26 inch barrel,

i might have been to close i was around 6-8 feet from the barrel,

loads grouped better than anything factory i have shot out of this gun,

speeds were very consistant throughout the different loads. best i got was a 10 fps between, worst was 50 fps between.

I shot two groups on the minimum end of the scale around 70 grains and even they shot around 3100, off the top of my head i think the book says they should be around 2800.. so everything was fast.

i will check sensors.
thanks
 
It sounds like an off calibration in the crony......

zero the rifle @ 100y.

shoot rifle at 300y.

go to a balistics calc and change velocity #s untill you have the results you are showing (measurement of group + or - from POA)...... the actual velocity should be reflected by the calcualtion derived from the balistics solver.

That is how I 'verified' my old crony was phukt. I bought a new one and it is accurate to the ballistics progams I have tried using this method.

To clarify, I figure 20 to 30 fps differance between crony readings and calcuated velocity to be accurate....... IMHO that is the differance between published BCs and actual BCs. Out past 300y the inital data becomes to ambiguous to be reliable for a test like this.

Cheers!
 
how close are you to the unit? Make sure you are back far enough that the muzzle blast doesn't reach the unit. I was getting weird inconsistent readings from my chrony that made no sense when compared to the book. i moved it further away and the readings sorted themselves out
 
just having some fun said:
hat is a tough one if it was 100 fps i wold say sure and back off a tad

If it was more I would say too close to Muzzle

One way to check is to save a few Factory rounds to check
Click to expand...

X2
If you are too close to the Chrony with a heavy charge, the muzzle blast could upset the reading. I'd try it again at 20' to be sure. Checking it against a factory load isn't a bad idea.
 
Find a buddy with a chrony and compare - you both will get a chance to verify readings. Distance is important, chrony specs. 10' for rifles. More tips from their instructions:
"

OTHER TIPS AND HINTS

Make allowances for temperature differences between chronographing your loads and their use in competition. In cold weather, powders burn more slowly and will produce lower velocities than they will at higher temperatures. Different altitudes may also affect velocity. Loads developed which are near maximum velocity during cold weather may produce dangerously high pressures and be unsafe during hot weather. Always try to match conditions while chronographing with those conditions you will face when shooting or hunting. That is, if you hunt in late autumn, do the chronographing in late fall.

ALWAYS WEAR EYE AND EAR PROTECTION WHEN CHRONOGRAPHING.

On sunny days, at certain angles, light may reflect from the bullet and cancel the bullet’s shadow. Mark the bullets all the way around with a dark-coloured felt marker if this seems to be happening.

On sunny days, the Chrony may be tilted sideways toward the sun, so that the Diffusers are between the sun and the photocells. Be sure that the Chrony unit remains fully open, and that it is perfectly aligned with the target. Using diffusers on cloudy days may shut out too much light.

Using diffusers on cloudy days is not necessary, since you have the clouds as a white background for contrast."
 
nwt2002 said:
okay first off i havent shot my chrony... good start.
I bought it a couple years ago but it finally made it out of the box yesterday, i was testing some loads for my 300 win mag, however the bullets where fast really really fast.

the load: 300 win mag, barnes 168ttsx, imr 4831 72.0 -73.0, cci mag primers

the loads started around 3300 fps and ended around 3500 at 72.8.

the book says it should be around 3100 ish.. okay id love to have bullets shoot that fast... but somthing aint right.

fired brass look good, nothing obvious for over pressure. ..

any ideas.
thanks
Click to expand...
this sounds awfully familiar.
Rem 700 SPS/DM 26" bbl same caliber, 74g RL22, 165g Nosler BT = 3300+ fps.
bullet was loaded overlength.
same ammunition in my friends browning 24" bbl was roughly 150 fps slower.
don't know if this helps but there you are.
 
make sure your chrony is in the shade, or try it on a very cloudy day. I have had some wild readings when the sunlight hit the bullet...
 
Mine does the same but not on a consistent basis....last week my 22-250 was launching 55gr. bullets at nearly 4000 fps when I was pushing them at 3700-3750 a few months ago with a very Temp stable powder....go figure.

Im starting to think about investing into a higher end chronograph.
 
Just going off of a hunch here, but try shooting the same load with a different 168gr bullet over the chrony...

I also agree with the other guys about trying a 2nd chrony and making sure you're at least 15-20 feet away from the chrony in order to ensure that your results are not being skewed by muzzle blast.
 
I have had this exact thing happen with the same chrony.I was getting SDs of my 308 in around the 4-9 fps mark which was fantastic until the sun broke through the clouds and changed the readings by almost 300 fps!
When the sun went back behind the clouds things went right back to within 4-8 fps again.Possibly try putting some cloth across the shields to make a consistently shady spot over the chrony.
 
When those chronys aren't dropping shots they're makeing up numbers. After a while you get tired of guessing which readings are bad, guessing what the reading would have been if it actually worked, makeing up velocities to make a ballistic program say the same thing as the drop chart, and getting a string of freakish readings.

A small group of us that compare notes a lot abandonned our chronies for CED M2s. Life is good again.
 
You must log in or register to reply here.
Back
Top Bottom