Hi,

I did some chrony testing today and was supprised that I didn´t get more speed out of my 6.5x55. Had three loads of VV 165: 2.60, 2.70 and 2.80 grams (low due to the gun being very tight) and I received speeds varying from 707 to 720m/s.

After the shooting I tested Lapuas factory FMJ rounds and only got 720 m/s (I use tham as a "standard")!

Last time I shot the Lapuas they gave me 800 m/s , the temperature then was 0C. Today the outdoor temp was -13C.

Can temperature affect the velocity that much?

cewe,my guess is barrel wear.Unless you are starting out with ammunition and a gun that has been left out in -30C for a couple of days.Then I would suspect the temperature,but this is just my guess.

Hi,

Thanks for the info and the charts. I discussed this with my gunsmith and with boha and both suspect the chrono. I´ve only used it three times but I cant see that I´m doing anything wrong -pretty foolproof contraption.

Tomorrow I´ll test a longer string using a .22LR with ammo that should be around 300 m/s. If this doesn´t work I´m returning the chrono. It´s given me readings that are way under load specs and the barrels should be OK.

I seem to have a nack for picking lemons.

Clem: I used the diffusers even on overcast days (I just like the setup, looks professional) and still get variations. I checked my notes and there is no logic to the readings I get. I´m returning the chrono and expect a new one instead.

I would suspect the cold temperatures are making the chronograph unreliable.

Cold batteries don't work as well. Electronics have a normal operations temperature range too.

I wouldn't trust any chronograph below 0 degrees C (32 degrees F): "Reason Freezin' "

Too hot would be no good either, for me and the chronograph.

I would prefer to chronograph between 40 degrees F and 100 degrees F ambient temp.


What I have seen:

Varget and H4350 Extreme: 1/2 fps per degree F
RL-15: 1 fps per degree F
IMR-4350: 2 fps per degree F.

I don't know how sensitive to temperature the VVN's are.

Powder type and ambient temperature effects on the chronograph are both important, as is the lighting factor from a winter sky.

RIP: According to my gunsmith VV powders aren´t easily effected by temperature but of course electronics are. But Boha has used this same model in the cold with no problems -cellphones are much more complicated and work well in subzero temps.

I´m putting these results down to "faulty wiring" and returning the chrony.

cewe:

According to the instruction manual that accompanied my chrony, the operating temperature range is 32°F (0°C) to 140°F (60°C). Also, the ambient temperature must be above the dew-point temperature. You may want to check your instruction manual to see what the operating range is for your unit before paying for shipping.

Cheers, Al

Al,

You have a point there Al. I´ll check before shipping it off.

According to the NRA "Facts book" a test in 1930 with natinal match ammo showed a 1.7 fps change for each degree F tenp change.
I`ve seen referance to a 2 fps change / degree reported in one of the load manuals I`ve got but don`t remember which at the moment. This follows pretty close the findings from 1930 and is what I use as a "rule of thumb". It also follows Steves tables fairly close.