bobh918
Here are a few pics of my chrono setup - in a box (sounds like a comedy club line). I set the chrono on the bench with a rifle aligned with the openings in the box and chrono to show their relative position and for a sense of scale. When actually shooting, the spacing is of course greater; 10 to 15 feet between.
The first pic shows the vertical slot cut in the front panel. There is an identical slot on the opposite side. The blue tape outlining the cutout makes it identifiable in the scope while the two horizontal tape lines are a reference to where the horizontal reticle line should be to prevent shooting the chrono. The black marker line identify the open area inside the chrono through which the bullet should pass.
The second pic is from the shooters perspective but slightly offset. Notice in the slot there is another piece of blue tape. This is actually on the chrono and serves two purposes; A) an additional aid to alignment and B) an additional screen to block any muzzle blast that makes it through the box opening before it gets to the first electric eye. Just over the muzzle in the pic, one can see the back opening.
The third and fourth pic show the chrono inside the box. The 3/4 x 6 pine is cut to fit snug. The witness marks on the inside/bottom are for alignment when setting up. At the moment everything is just cut to fit tight and/or taped in place. Now that I know it works, I'll fasten it with some hardware.
The fourth pic shows the LED lights the best and the second panel of tape described earlier. This tape panel was the original attempt at shielding the electric eye. There is a hole in the bottom of the box to allow the power cord to be connected. It's in the shadow. The Light kit runs on 12V DC and I've run this setup about 4 hours total off my auto jump starter without recharging and the battery is only down the slightest. I could probably run it 20 or 30 hours but according to Murphy, that's when I'll need it. The LED's use hardly any power.
When used, I just place the box on the ground and align the rifle to shoot through it. A few scraps of 1 by and 2 by lumber act a cribbing to level and the scrap of 2 x 10 on top (pic 1) acts as ballast to prevent the muzzle blast from knocking the alignment out.
With the unit setup and the boxtop closed, the advantage in using this contraption is minimal interference from varying light conditions and other outside sources including wind, muzzle blast from another shooter, smoke if they're shooting blackpowder or any other similar interference. It works equally well on sunny or cloudy days; at any time of day because the dark interior is only illuminated by the LED indoor light set, the light is consistent hence the degree of accuracy should be consistent given all else being equal. the short answer is we've taken the inexpensive chrono and shielded its achilles heel.
As others have suggested, take your chrono numbers and the data you shoot at distance and plug those numbers into your ballistic calculator for your true drop data. Keep in mind the Chrono numbers may be off slightly when compared to the calculator but that will most likely be an inaccuracy in the chrono. Since I started using this setup, my chrono is always a few FPS slow when compared to the ballistic calculator but my drops for in between distances are dead on with the .223 in the pic above. The key is they are now consistent and recognizable.
I hope this helps with one aspect of the problem.
