I need to chrono my .300 mag for a new CDS scope dial. I have a run of the mill Caldwell Chrony. The basic one with the aluminum rods and plastic sun shades. The manual says to set chrony 10-15 ft in front of barrel. When I do I got two good readings and several errors. I was able to fully chronograph dads .270 with no errors. Would the blast of the .300 be throwing the errors? Any info or ideas would be appreciated.

The biggest issue I have found with that style is chronograph is the light it is getting, a cloud coming over or if you are under trees and the breeze changes shadows the results can can greatly. As far as blast goes I’ve never had an issue shooting a 300wm that close

Yes. Happened to me once. Move it on out to 20 feet or more. Then try not to hit it.

Yep those types are such a pain . Either the lights not right , too much muzzle blast ,, your a 1/4" off center always something

move the chrono out a bit more

25-30 feet

They need natural cloud cover or the plastic shade.

IMO yes, I messed mine up by shooting too close. Concussion .

When I send off for my new leupold CDS, would moving the chrony that much farther effect my bullet velocity info needed to calibrate the dial? Thanks for the info you all.

The 2 shots that read averaged out to 3150fps. I believe I leupold wants the average of 5 shots.

I'd sell you a lightly used magneto speed chrony and you would be good to go.

Thanks for the offer Yes Sir!. I'm going to try out moving mine out to 20 feet. I rarely use one.

if you calculate on a MV of 3000fps with a 168gr BTHP you have 37.2 inches of drop at 500 yards

if you figure that has a 30 foot velocity of 2981 by using the calculator to give you the velocity every 10 yards.

then rerun the original calculation with a MV of 2981 it is 1/2 inch at 500 yards more drop with the 19fps drop in velocity

if all your rounds are firing withing 20fps you have some of the most consistent ammo ever

so the round to round difference in your ammo of 20fps would make a larger difference than pushing your chronograph out to 30feet from zero feet so the difference in 20 to 30 feet is going to be a 1/3 of that

or not really enough difference to worry about , other factors like temp and air pressure will make a bigger change.

Thanks Pete. Actually tried PMing you, but your basket is full. Yes, the 2 shots I was able to read were 60fps different. I'm shooting 165 ballistic tips on 72gr. of IMR4350. Funny, about 10 years ago, same Browning Abolt2 was only shooting 3030fps. I could just stick to inches on the dial, but I really like the yards in the CDS.

Personally I do a 10 shot average for turrets. You want to be as accurate as possible with the fps if your gonna be using it out to long range stuff.

I have a similar chronograph and only occasionally have a shot that doesn't get read. Out another few feet may solve your problem. I take a lot of care to get mine set up on a tripod and aligned properly. Having the rifle in position on the bench and lined up with the target lets me align the chrony using the view through the scope backwards (through the front end). Then also check from behind the rifle for parallel through the chrony - no tilt up or down or side angle to create an error in the reading.

The interrupting light chronographs are also real touchy on height over sensor.

My old shooting chronys sweet spot was 3-5” inches over the sensors. Any higher or lower and I’d get more errors.


I bought an Athlon radar.

Even only using a chronograph 2-3 times a year, it was money well spent and I find myself chronographing stuff all the time now since it’s literally “point and shoot” setup.

I broke down and bought the athlon about a month ago too. After going to all the trouble of developing a load that was really accurate at 200 yds then finding out my ES was not good when checking the speed to take it out to a 1000 I decided I wanted velocity on every shot through load development.

Im just getting into the long range game but a ballistic calculator seems not to be right on when I get out to farther distances. Its close but not close enough. Me personally I'd feel more confident in shooting at distances you are planning on shooting at and getting the real dope rather than just getting dope off of velocity and published bullet BC. But maybe I'm missing something in my process.

I’ve found advertised BCs arent always what they claim.

And velocity too.

I’ll usually fudge my velocity till what I’m seeing down range jives with what the calculator is spitting out. (Of course making sure all environmentals are precise).

TRASOL has a feature called “drag coefficient”. I’m not sure exactly what it’s a measure of or what it changes in the math, but you can move this up or down to “tweak” the dope to fit.

Athlon, Athlon, Athlon!!