Weird Chrony Readings

[Mtaylor]

Can anyone explain to me what they think happened here? Sunny day, 70 degrees, wind 10 mph, shooting 7mm Rem Mag Tikka T3 Lite, shot cold bore through it 150 gr partition at 2700 ish fps ( I can't remember exactly but it was not drastically off from what I thought it should be) next 5 shots were hand loads, 60 gr IMR 4350 under a 160 gr Nosler AB. The errors shown in the picture were not shots. I gave the gun 1 min between shots to cool. Using a Caldwell chrony.

 

[mtswampfox]

currently use a magnetospeed partly because my pact chrony was a pia. even after switching out to infrared screens it would get goofy tho not as much have heard a bright sunny day is the worst time for getting consistent readings even with the diffusers in place. only use mine now for around three shots to verify a load. put more importance on downrange accuracy than speed

 

[N2TRKYS]

That's some crazy speed swings. Do you not take a pic of your target? I have the same chrono and love it. How was accuracy?

 

[GKPrice]

View attachment 40719Can anyone explain to me what they think happened here? Sunny day, 70 degrees, wind 10 mph, shooting 7mm Rem Mag Tikka T3 Lite, shot cold bore through it 150 gr partition at 2700 ish fps ( I can't remember exactly but it was not drastically off from what I thought it should be) next 5 shots were hand loads, 60 gr IMR 4350 under a 160 gr Nosler AB. The errors shown in the picture were not shots. I gave the gun 1 min between shots to cool. Using a Caldwell chrony.

View attachment 40719

did you work up to the 60.0 grain load ?

 

[Mtaylor]

Accuracy was good, 2'' at 165 yds is in the acceptable range for my ability right now. Yes I did work up, I started at 56 grains and worked up to 62.5, I did a ladder test a few months ago, I shot all of them through the Chrony and picked 3 loads I thought had potential then made up 5 rounds of each. The other two groups were 61 gr and 62 gr IMR 4350 all 3 loads had similar group sizes. I do think a lot of it has to do with the sunny day factor. I wanted velocities because I have a Vortex Diamond back with hash marks in the reticle, then I would take the average velocity plug it into Vortex's ballistic calculator and get the ranges each hash mark would shoot to (like what Robby D. Did with his 270 wsm last year).
View attachment 40732

 

[Mtaylor]

Sorry picture is upside down

 

[N2TRKYS]

IME4350 was slow in my buddy's 7 mag. IMR4831 gave better velocities and accuracy.

 

[mtswampfox]

Hate to butt in again ,just assuming mag primers?and would de-burr the inside flash hole.

 

[rayporter]

the first shot is a calibration of some sort and should not be included in a string.

my first thought is too much sun. i have had trouble with bright sun in the past.

 

[bates]

Id try a different chrono

 

[pods8 (Rugged Stitching)]

1) 2700fps for 150gr out of a 7mag sounds a good 300fps slow (were these purposely downloaded)?
2) Sun is a PITA on chronos, sometimes I have had to wrap craft paper (that brown paper) around my unit and screens to make a shaded tube to shoot through.

 

[Mtaylor]

Sorry for the late update, a few weeks after my initial thread of weird chrony readings I tested my chronograph again on a cloudy day. Everything worked well with all of the readings. I think my first readings that were screwed up were caused by the sun and the wind conditions on that day.

Matt

 

[N2TRKYS]

Man, that's awesome. Did the speed increase?

 

[Mtaylor]

Yes it did, up to 3000 fps

 

[16Bore]

Sun will really mess those things up. Gotta be sure it's level and all that crap. I took the wire between the screens and the readout and put a loop in it to go around the leg on my rest. That way I know the distance is always the same. Once I got it set up where I wanted, I marked the tripod legs with a sharpie so it's easy to reset the next time. And use the same bench at the range as well (ours has some funky grade at the forward position)

If you've got a 22LR, it comes in handy as a "checker" when you do get things set up. Any spot on a 4'x4' piece of cardboard at 100 yards will read fine so you're able to shoot groups and watch velocity at the same time.


Oh, and on the screen brackets (cloudy days I don't bother with the diffuser) I wrap orange tape at the middle as a check when lining everything up.

 

[16Bore]

Neat little run up I did with my 260 and 108 Scenars.