Canadian Airgun Forum

I have finally decided to try something more complex than polishing trigger mechanisms.

I'm converting a Crosman 2240 to .177, using a 1377 barrel. The idea is to create a quiet pistol for shooting paper targets at short range.

I knew that the longer barrel and lighter pellets would put the gun over 500 fps, so a chronograph was required in order to track the detuning process.

I wanted to synchronize the data to my Mac, and keep my costs down.

In the end, the Caldwell Ballistic Chronograph seemed my best option.

I shoot in a basement range, so I knew from the beginning that I would need an alternative lighting solution.

After watching YouTube videos about building isolation boxes, and others about using dollar store LED illuminators, I decided to skip the deluxe package with the IR lights, and go for the base chronograph with data cable. I got it from Cabelas for $137 with free shipping.

The package arrived in rough shape, but once I got the Chronograph out of the clamshell, it turned out that there was no damage.

The chronograph was easy to set up, and the instructions were quite clear.

Synchronizing with the free Caldwell app on my iPhone was easy. This is my planned route for producing shot data in a format that I can import into Excel for Mac. It logs all my stats with a minimum of user intervention.

Sure enough, I was getting a lot of error 2 and 3's under a mixture of LED and fluorescent overhead lighting, just as I expected. Shutting off the Fluorescents didn't make much of a difference, reducing the number of errors, but increasing the number of shots that didn't register at all.

I had already bought a pair of dollar store LED trouble lights, with the 24 LEDs in a 3 * 8 array. Placing them on top of the diffusers helped a bit, as did moving them under the diffusers, and taping them in place.

In the end, I built an isolation box, using the cardboard carton from a stereo speaker.

The box was approx. 18 inches by 14 1/2 inches by 13 inches, too small to hold the diffusers, but I already suspected that they would be irrelevant in an isolation box.

I set it up with trapezoidal shooting ports at each end, the LED flashlights shining straight down on the sensors via holes in the top of the box, a small window to view the LCD display, and flaps on each side to facilitate connecting the data cable and turning the unit on and off.

I mounted the box on my tripod by cutting a 1/4" hole in the bottom of the box. The tripod screw was just long enough to go through the box and secure the chronograph.

Sure enough, I went from about 50% valid results, to 100%. I did a long test session with zero errors this evening, and no interference from a pair of fairly bright LED chandeliers..

My total investment in the isolation box was a few cents for duct tape, and $6 for a pair of LED flashlights.

Based on other people's experiences and the performance I'm getting with my home-made LED illumination system, I recommend that people skip the "deluxe" package with the tripod and IR lights, if they are looking for good performance in an indoor range.

Buildilng a cardboard iso box is a breeze, and the results thus far have been excellent!

Would really like to see some pics of this setup.

_________________
A mask is not a political statement. It is an IQ test.

As requested, cel phone pix of the prototype ChronoBlaster 2500.

Crude but effective, kind of like me...

Additional pictures.

Note that the bottom of the shooting apertures are 3" above the top of the chrono. If I accidentally shoot the Caldwell with this setup, I deserve a kick in the butt.

A word about safety, cost and effectiveness: This was supposed to be a prototype for a wooden version, but after using it, I've decided that cardboard is better, for a couple of reasons.

Ease of use:
[*]Cardboard is light, and doesn't stress the tripod.
[*]Easily replaceable.

Safety/Economy:
[*]There's nothing of value more than 4" above the tripod head.
[*]A stray shot passing through the upper part of the box won't break a diffuser, or tear a support rod out of the housing.
[*]The likelihood of a ricochet off a poorly-placed shot is minimal.

Thanks for the pics. About what I expected but good to be sure.

I wonder what aspect of the box is responsible for the considerable improvement in functionality? Is it the elimination of any exterior light sources, or the narrowing or focusing of the light beams? The box is pretty reflective inside so there is still considerable light bouncing around in there - I wonder if spraying the inside of the box with flat black would be a good idea?

Just thoughts on my part. I can't argue with your success. 100 % is hard to beat.

_________________
A mask is not a political statement. It is an IQ test.

This was an interesting project.

Note that the pools of light from the flashlights are pretty much circular.

Strange, given that the LED arrays are rectangular, and so are the box cutouts:

I'm no expert, but with the Caldwell, at least, I don't think that reducing internal reflection in the box is necessary. The sensors are buried about an inch and a quarter below the top surface, in a narrow, dark, non-reflective cavity.

As you can see from my pictures, while the box looks pretty well-lit from the shooter's perspective, when you look down into it from above, it's clear that the sensors are centered in pools of light that are much brighter than the ambient light in the box.

I noticed a pattern of specific things that seemed to work for other chronograph users. Success mostly seems to center around reducing interference from stray light and muzzle blasts that could affect the reading, increasing the intensity of the light, and creating a more diffuse light field.

Here is a list of what improved accuracy for other users, across a variety of chronograph brands:
[*] Switching from a 3-point light source, to one with a larger array of LED's.
[*] Using a wider light source, to ensure even coverage across the length of the sensor port.
[*] Suspending a blanket or cardboard roof over the diffusors, after providing an electronic light source.
[*] Sticking bristol board side panels to the diffusor support rods, to reduce reflected light coming in from the sides
[*] Reducing the muzzle blast by moving further back, or having a smaller opening in the front panel of an iso box.

I've been shooting with the muzzle of my pistol at a distance of about 4' 6" from the box.

Now that I'm getting consistent numbers, I'm going to try moving closer.

Ideally, I'd like to take my velocity readings within a foot or so of the muzzle. I want to be sure that if the police ever had reason to send one of my guns out for testing, I would come in comfortably under the legal limit with standard pellets.

Even there, I should maybe consider picking up a small tin of alloy pellets.

I'd hate to be shooting at 490 with my 8.2 gr RWS MeisterKulgen's, and then discover that I tested over because someone used 7.5 gr pellets. Or even 5.4's, like the red Crosman Penetrators...

Anybody know if there's a standard, i.e.; 7.9 gr for .177, and 14.3 gr for .22's?

You have obviously did a lot of research on this. As soon as I catch up on a couple of other projects I intend to start playing around with my Chrony. I guesstimate I am getting about 90-95% good readings with .22 pellets and 75-80% with .177. I am using the slightly smaller puck lights generally sold where you see your type. They have 4 rows of 6 leds and I have them attached to the underside of the diffusers.

_________________
A mask is not a political statement. It is an IQ test.

The Replica Airguns guy on YouTube started out with 3-LED puck lights, and switched to the kind you have. He still gets occasional errors, but it seems to work fairly well for him, too.

You might want to try rigging some sort of barrier to hang over your existing rig. A couple of sheets of bristol board from the variety store and some masking tape, or even a blanket and some twine to hang it, would probably be good enough for a proof-of-concept.

If blocking direct light falling on your Chrony from overhead and the sides further improved your accuracy, that would be a pretty good litmus test for looking at some sort of isolation box.