Chrono Questions?

[Brux]

I have a Caldwell. I don't think its reading right
24 inch bartlein barrel in 308
42GRS RE15 or 42 to 42.5 of varget 168 SMK running 2730,2740 in Lapua brass FL sized 210m primer
I was doing load development and 43.5 to 44 GRS varget i'm at 2830 with a 175 SMK
What do y'all think and is there a way to calibrate or check these?

 

[straightshooter1]

I have a Caldwell. I don't think its reading right
24 inch bartlein barrel in 308
42GRS RE15 or 42 to 42.5 of varget 168 SMK running 2730,2740 in Lapua brass FL sized 210m primer
I was doing load development and 43.5 to 44 GRS varget i'm at 2830 with a 175 SMK
What do y'all think and is there a way to calibrate or check these?

Yeah, looks like somethings definitely wrong with that chrono. Though you didn't state what you COAL is or if it's "new" brass, if I plug some numbers in and assume it's a high pressure load without going too far over the SAMMI max pressure of 62,000 psi, I'm not seeing anything close the that kind of velocity.

For example, in using my QuickLoad app with a cartridge in new condition where the cases volume for Lapua is around 54.5 gr H2O and the bullet seated at SAMMI spec (2.800") and even to put it up more at at temperature of 100°F, QL calculates a velocity at 2703 fps using 44.0 gr of Varget pushing a 175g SMK. Also, QL app shows 44 gr of Varget is filling the case to 106.3% of cases capacity at that seating depth. With my 26" Krieger barrel, I've gotten 2,694 fps using 43.6 gr Varget pushing the 175 SMK, which I measured with a MagnetoSpeed V3 chrono.

So, based on these number, IMO, your chrono is out of calibration. Or it's not reading correctly because of lighting conditions???

 

[supercorndogs]

Check the chromo numbers VS drops at 800, for the .308.....1k for everything else. ? ?

 

[MTRecon]

I have both a Pact Professional and a Chrony...they differ from 75 to 150 fps...never been able to find a way to calibrate either one...I plan to borrow a couple other chronos from others and see if I can average them or get a concensus...

 

[straightshooter1]

I have both a Pact Professional and a Chrony...they differ from 75 to 150 fps...never been able to find a way to calibrate either one...I plan to borrow a couple other chronos from others and see if I can average them or get a concensus...

. . . or just get a more accurate and reliable chrono, like a Magnetospeed or LabRadar.

 

[Brux]

Yeah, looks like somethings definitely wrong with that chrono. Though you didn't state what you COAL is or if it's "new" brass, if I plug some numbers in and assume it's a high pressure load without going too far over the SAMMI max pressure of 62,000 psi, I'm not seeing anything close the that kind of velocity.

For example, in using my QuickLoad app with a cartridge in new condition where the cases volume for Lapua is around 54.5 gr H2O and the bullet seated at SAMMI spec (2.800") and even to put it up more at at temperature of 100°F, QL calculates a velocity at 2703 fps using 44.0 gr of Varget pushing a 175g SMK. Also, QL app shows 44 gr of Varget is filling the case to 106.3% of cases capacity at that seating depth. With my 26" Krieger barrel, I've gotten 2,694 fps using 43.6 gr Varget pushing the 175 SMK, which I measured with a MagnetoSpeed V3 chrono.

So, based on these number, IMO, your chrono is out of calibration. Or it's not reading correctly because of lighting conditions???

It's 3 times fired brass. Seating at 2.800 right now because of trying to do load work up. But that's only 40 thou off with this chamber.

 

[straightshooter1]

It's 3 times fired brass. Seating at 2.800 right now because of trying to do load work up. But that's only 40 thou off with this chamber.

The work ups I do in QuickLoad don't give precise results, but do put me in the ballpark (like within 20-30 fps, usually better). So with the the change in volume from a new case to a 3X fired brass, the volume is decrease resulting in a lower velocity, so there's an even greater difference far away from being in the ballpark. I'm very confident that that 2830 fps your chrono showed isn't anywhere close to your actual MV.

 

[Brux]

Thank you for your help.I will call Caldwell Monday.

 

[Cerwinski]

Make sure you set it up far enough away from the muzzle (at least 12 feet or so). Otherwise you can get inaccurate readings off the powder particles/gasses.