Range Report Cheap F1 chrony.... worthless? Or valuable tool? Confusing results at the range...

[ScottyD]

I'm a newb to re-loading and I've been seeing some weird stuff happen lately. I've never had a reason not to trust my chrony, I've shot arrows, airgun pellets, and rimfire bullets through it and the numbers always seemed to be on track. The F1 never gave me any reason not to trust it. My buddy shot some 155g scenars through it and the F1 told us he had a node at 2950fps. He plugged that velocity into the JBM program and his numbers were only off .1 of a mil at 1000yds! Then I shot my 6.5cm through it and it was showing me 2900fps with 140g A-max bullets (42.7g of H4350 through a 25" barrel 90 degrees F, 25.0 inMg). When I went out and shot, my numbers were WAY off. I had to adjust my velocity from 2900 to 2700 to get my "Bullet flight" app to match what my gun was actually doing at the range. Bullet flight doesn't work on DA: Instead you put in temp and pressure (I input current range temp and pressure conditions straight from a barometer/altimeter that I keep with me). I've been over and over the info I'm plugging into the Bullet flight app, and I can't seem to find any glitches with the data I'm putting in. So could my chrony be that far off with my A-max bullets? Any other things I should look into? Something doesn't seem right to me. What seems more likely:My 140g A-max load is really doing 2700fps, or 2900fps in the conditions mentioned above?

Any suggestions or advice would be most appreciated!

 

[SigsauerP229]

Not worthless but finicky due to conditions. It always seems to have minimal velocity spreads with my loads on a given day but I have had it show 100 to 150fps differences on different days due to different weather conditions. I recently bought a used Oehler so will see if it was worth the cost upgrade.

I guess it was worth it just to get an idea but it seems like I have to have the sun right overhead to get a good reading. I have a Pact that is almost 20yrs old that is less finicky. I bought the F1 just because the Pact was so old and I wanted to confirm the speeds but now I wish I just bought the Oehler right off the bat due to the fact that so many seem happy with them.

 

[ScottyD]

Thanks for the info. Good to know a 100 to 150fps difference due to light conditions is not uncommon...

 

[308Gunner]

+1 I will see 100 to 150fps differance in days when cloudy compared to bright sun light.

 

[0311@LAR]

Not worthless, but more of a "ballpark" figure than exact science.

 

[Greg Langelius *]

Chrony (and other optical) chronos will report an erroneously high velocity of they are set up too close to the muzzle. For large rifles, the distance should be 10-15ft. The muzzle gasses will outpace the bullet and can get picked up by the optical sensors. The additional distance allows them to dissipate to the point where they cannot be sensed.

Chrony's Instruction Page

Most chrono producers specify an error percentage of .5% to 1% if the reported velocity. For a reported velocity of 3000fps, this error factor can be on the order of 15-30fps above or below the reported velocity. Obviously accepting values that can be off over a range of 30-60fps makes certainty about ES/SD values less than that rather dubious. Therefore, the preceding post has added meaning.

I currently have onhand an Alpha and a Beta that are unusable. I am budgeting to replace them both with Alpha Masters sometime in the next 3-4 months,

Greg