Wednesday, May 14, 2014

Rain, rain, go away...

I had planned to go to the range to get comfortable using a chrono today, and it's supposed to be piss-pouring down rain all day.

Chronographs have always been faintly mysterious things to me; things that other people owned and set up and then asked me to please be careful not to shoot. It's time for me to demystify them, so I'll be trying out both your classic Chrony and this funky new Magnetospeed doohicky, once the monsoon ends.
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17 comments:

Firehand said...

Picked up the base-model Chrony a few years back, interesting gadget. And it's nice to find out exactly how fast a bullet from your handload/that brand is actually going from YOUR firearm.

For places with wind like Oklahoma, strongly suggest a couple of stakes for the kit, so you can keep the tripod from blowing over on those days.

Scotty said...

Ha. Chronographs are simple beasts. Two light sensors point a the sky; when the first one sees a shadow, it starts a timer. When the second one sees a shadow, it stops the timer. The sensors are a known distance apart, and distance / time = speed. Then, obviously, once you have speed you can figure out the ballistics. The flat piece of plastic above it is to keep random objects like birds or clouds from triggering the timers, but it also helps give you a place to aim. I have the RCBS version and like it / would buy another if I were to have an accident.

Wouter de Waal said...

The magnetogadget is nice but way above my budget at present.

1911Man said...

Four words: scope height over bore. Remember them. :-)

Scott J said...

Bought a used ProChrono off eBay a couple years back. Added a whole new dimension to the gun and reloading hobby.

Robert said...

We used them quite a bit when playing paintball, and set a 300 FPS limit. More than that and it started to hurt too much when they'd smack you, plus a higher risk of breaking a set of goggles.

JayNola said...

I would say I don't understand how people shoot Chronys but I've seen it happen and to this day still swear that thing jumped into the path of the bullet. Neither my bullet nor my Chrony. Lack of staking May have played a part in the casualty but

Ritchie said...

A laser boresighter can help you get things lined up, especially with things like ARs.

Anonymous said...

"...please be careful not to shoot..."

I thought that was the whole point of a chronograph: You shoot it, measure how far the pieces went and do the speed/energy calculations from there.

When I get mine back from the factory I'll have to try this new fangled "Try not shooting it, you $#@%@$# idiot" method.

KM said...

Wrap a piece of black electrical tape around the rods about 5-6" up after they are inserted in the Chrony. If you get your crosshairs/sights close to that tape, there is a very, VERY small chance of doing the dumb.
Even the highest scope won't put the expensive stuff in danger.

Scotty said...

One more thing I've found. Best way to set it up if your using a scoped rifle. Set the rifle on your bags or whatever, pointing pretty close to on target. Then take the chrono ten or so feet down range and put your head so that you can see backwards through the scope. Then line the chrono up so that its centered on your eye. Saves a lot of time.

Anonymous said...

>Chronographs are simple beasts. Two light sensors point a the sky; when the first one sees a shadow, it starts a timer. When the second one sees a shadow, it stops the timer

I'm surprised there's not an opensource design for skyscreens out there already. It seems that they're little more that a photodiode (sometimes you can use LEDs as photodiode, as they both emit and detect light depending on bias) Two rods (how about chopsticks?), a base (chunk of 2x4?) and that bowed plastic skyscreen thing (How about cutting up a cheap hardware store window blind?)

I feel like I could probably solder together ~20 skyscreens in an afternoon at the cost of maybe $2 each. Almost cheap enough to shoot.

-SM

LCB said...

Robert said:
We used them quite a bit when playing paintball, and set a 300 FPS limit. More than that and it started to hurt too much when they'd smack you, plus a higher risk of breaking a set of goggles.

Not to mention bleed/bruising with hits on bare skin when you go WAY over 300!!! LOL

Most paintball ranges in my neck of the woods put the upper limit at 200 or 250. Not that they actually enforce it or anything .

drjim said...

You can send your excess rain to SoCal!

Scotty said...

SM -- they are a little more complicated than that. There's a lens in there that concentrates the focus on a small sliver of the sky, and you have to hook them up to a pretty speedy PLC or somesuch to get the right accuracy on the velocity calc. But in general, yeah, they're pretty simple.

DJ9 said...

I was composing my message as I opened the comments window, and what should appear but Firehand's comment, which began almost word-for-word the same as the one in my mind. Scary, I tell you...

Anyway, I've had my base-model Chrony for almost 2 decades now (early adopter), and although it doesn't get used as much as it did in the first few years, I still break it out and check some loads every now and then. It still works just fine (when checked against newer/more-modern models, it's always very close), although the old cardboard "oval window" aiming guides (pre-metal-rod model) are getting pretty worn (read: shot-up; mostly from snubby revolver and pocket pistol testing).

Every serious shooter and/or handloader should have a chronograph, IMO.

Alien said...

I'll chime in with another "don't shoot the chronograph" tip: set up a target to shoot at through the chronograph. Dual benefit - with an aiming point there's less chance of shooting a screen, and you get accuracy/group size measurements simultaneously with velocity data.

For easier setup (I use an Oehler 35) I used a bright AA flashlight centered in the rear of an 18" plastic pipe set level on the bags. Boresight the pipe where you want bullet impact downrange, insert flashlight. Downrange you can see the light only when lined up with the pipe, adjust screen position, then target position, with that reference. Couple of cheap magnetic base bubble levels help, too (the 35 uses 1/2" EMT to support the screens).

I suppose these days a bright laser could be substituted, but I'd suggest correct nanometer laser glasses as eyepro.