Chrono numbers higher than expected

[tstith]

I tried out my new Caldwell chrono today. Yes, I know it's not a magneto and it's not high end. It functioned with no problems but the readings it was giving with several loads was considerably higher than anticipated. Examples: A 16" AR with basic 55gr FMJ factory ammo was shooting 2880fps. A 300 PRC with 220 ELD-M factory ammo, box says 2810fps was shooting 2950fps on this chrono. My 300WM 212 ELD-X (76.1gr H1000, Fed 215GM, Hornady case, 3.595" COAL fired from 26" barrel with suppressor) load was thought to be in the 2850fps range, chrono showed 3021fps. 308 150gr SST (41.6gr H-4985, federal case, Remington 9.5 magnum primer, 2.795" COAL fired from a 20" barrel with suppressor) was reading 2759 fps. Both of the handloads powder charges are on the lower end.

Elevation was about 4400' if that matters. Followed the manual so procedurally testing was conducted right.

Has anyone had a similar experience? The 300 PRC, 300WM, and 308 velocities seem about 150fps high to me.

Thanks ahead of time for your input.

 

[Gunnersdad49]

Chronos are like boats. Way better to have a friend with one than maintaining one yourself. I would try two things if you can.

first, compare your loads over your chrono and another and see if they read the same.

next, or if you don’t have a friend with a chrono, put your data into a ballistic calculator and see if the drop you see is the same as what the app states. If it jives, you are good to go. If your bullet falls more than the calculations say it should, you might have a chrono issue.

 

[tstith]

That was my course of action but wanted to check the Rokslide knowledge to see if these numbers sounded too outrageous. I don't have access to another chrono

 

[Rifles And More]

I always took a 22 rifle to the range with the same ammo. It was my control group for the chronograph - if it was the same every time, I figured the chrono was set up right and working. If it was reading high, I expected everything else to read high. Keep a logbook.

 

[tstith]

@Rifles And More I'll give that a shot this morning and see about the results. Thank you

 

[Johnc427]

I would be hesitant to believe those numbers. I had the same issue with a Caldwell and upgraded to a Magneto, because I was having a 300 win mag with 215 bergers show 3k+ when normally it was in the 2800 range.

 

[tstith]

Update: I tried out a couple 22's and got consistent results. I also tried 9mm out of a G17 and G19. The numbers were consistent with advertised velocities. I tried the 300WM and 308 again and got more realistic numbers. 300WM was pushing ~2950fps and the 308 was pushing ~2640fps with 150gr (mild load) and ~2575fps with 180gr. Groups fired at known distance with the updated velocity were consistent with these numbers. I did note the suppressor did give a slight boost in velocity

 

[Rifles And More]

I shot my chronograph when I tried pistol...

Glad to hear it is working. Take those 22's every time to get things set up.

 

[Rich M]

I have a caldwell chrono. It seems to be consistent and accurate.

The trick is to have a known load to verify the rest.

I do keep a reloading log and list speeds and cut and past the actual targets for the load & bullet lengths when the target swill fit on the page.

FWIW - I've seen enough guys doing comparisons between chrono and magnetospeed. They've been pretty close, so I'm not convinced that magnetospeed has any real advantage. YMMV

 

[isocyanate]

Can you shoot at 700+ to verify drop? That's the best way to true everything up, whether you used a magneto or not.

 

[tstith]

Its pretty difficult to find the time to get to a place where I can shoot that far. A lot of places around here in the National Forest are not allowing recreational shooting due to burn bans

 

[Stefan]

Chronos are like boats. Way better to have a friend with one than maintaining one yourself. I would try two things if you can.

first, compare your loads over your chrono and another and see if they read the same.

next, or if you don’t have a friend with a chrono, put your data into a ballistic calculator and see if the drop you see is the same as what the app states. If it jives, you are good to go. If your bullet falls more than the calculations say it should, you might have a chrono issue.

I have played that game before. Used two different chrono's with the same load. Both chronos gave different velocities.

 

[tstith]

So I should get as many chronos as possible together, test a few rounds in each? Apply some science and math with a lab coat on? Find the mean of their velocities on a bell curve? :'D