Jim in Houston wrote:Now that I have my chronograph (ProChrono Digital based on info here and 5 star review on Midway's site), I am ready to take some measurements. From other threads, it looks like the preferred condition for measurement is with a "cold" barrel (i.e. letting the rifle cool down between measurements). Since it is running 100 degrees (or near enough) in Houston, "cool down" is a relative term.
Anyway, any tips on getting accurate readings (or ones that would be of interest to other board members), like how many rounds are needed to get meaningful results, how important is standard deviation, average and median speed, etc. Should I be measuring group size at the same time? I gather from other's experience I should avoid shooting the chronograph. Should I record temperature, wind, and humidity conditions? Anything else?
Barring any input to the contrary, my plan is to heat up the barrel with 20 rounds, then shoot strings of 20 with a hot barrel, basically to compare Hornady and Remington factory loads against each other under similar conditions and my reloads against the Hornady Handbook data .
Two things come to mind that have caused me issues with my Chrony F1.
The first bit me in the butt the first few times out. Depending upon how much unburned powder you're throwing out the end of the barrel as a function of burn rate, keep your distance. I initially set up about 8 feet away because that was as far as I could see without having the lighting just so. I have since gotten a remote display. Most of the time, I got accurate results within the speed I would expect, then faster than I expected velocities and back to normal. I moved the Chrony to around 12 feet away and that problem stopped. If I load with VV N110, it can still happen as that stuff throws what looks like sawdust downrange each shot.
The second phenomena still persists at the range I shoot at. I typically go for 4-5 hours at a crack and despite always using the sun screens, I will get 3-4 shots in a row that though they track one another like any other string, they are 1k or thereabouts fps slower. I usually go to the range at the same time of day when I go and over the course of those hours, the sun cuts the same course across the sky and given my choice, I sit at the same shooting position. After several episodes of this, I realized it happened around the same time every visit. I'm not sure if I'm catching a glint of light off of a reflective surface, or the pond immediately to my left between me and the sun, the dew burning off, or whatever, but I strongly believe there is an environmental factor at the range that at about the same time every day causes a short lived string of consistent low velocities. Then, just as suddenly as they manifest, usually after about 20 rounds of normal readings, the phenomena goes away. I've walked all around the Chrony and look for odd patches of light, but to no avail. I've turned it off for a couple of minutes, but to no avail. It may be passing through a temperature zone as it heats up in the sun that is causing it, I don't know and I've been in Electronics since 1971 More than that anecdotal observation, I am at a loss to explain what the causative factor is. So, be mindful of the sun's location relative to your own. It may play tricks that the user's manual doesn't touch upon. Some folks report that canting the chronograph slightly off to one side helps with oddities like this. I haven't tried that yet. Keep in mind that the further north you go, the less high the sun gets, even at the peak of summer.
This will come in time, but if there's a lot of pollen in the air and/or humidity, if other shooters are banging away on either side of you, they can false trip the chronograph from just the shock wave. I used jot my velocities down as fast as possible after the shot. The remote display has some basic recall features now so that's not as big a factor. I don't know what the one you bought has, so I mention it. Always bring a spare battery as they pick inopportune times to go south.
Also bring a lens pen and a squeeze puffer (or whatever they're called)to brush off debris that may fall upon the sensors.
Think of a real good, face saving reason to give other shooters as to why they can't shoot a shot or two over your chronograph. Something like it's calibrated to just your particular load, it doesn't belong to you and the fellow who you borrowed it from made you promise not to, or whatever you can say in a matter of fact way, with a straight face.
Hoot
