2 Box Chrono

[Bat Rastard]

I was thinking these looked like a clever gadget, but they seem to have left the market. Were they a good thing?
Did the Auto Trickler people discontinue it because they are buried in V4 orders? Or were they not popular? Or not good?

 

[Bat Rastard]

An update:
I bought one off of the classifieds here.

It is a fine contraption. I am not sure why this product wasn't a huge success.

 

[Twdmar]

The shotmarker is probably taking up all of their resources. I thought it seemed like a good idea as well.

 

[wwbrown]

One issue acoustic chronys have that optical ones do not is that to get accurate muzzle velocities you need the microphones to be carefully aligned with the axis of the barrel. The speed of light is so much faster than the speed of sound so the alignment is not as critical.

I designed and built a couple of chronys that use microphones about 10-12 years back and use them for load development to find loads that have low standard and extreme deviation. Before I built the acoustic chrony I worked up the math to understand where the errors were and I found them critical to alignment, if you want an accurate measurement of the muzzle velocity the alignment is critical, when developing loads a rough estimate of the muzzle velocity is not as critical as the spread.

The beauty of using microphones instead of non-illuminated optical sensors is the position of the sun or clouds do not impact your measurement. In addition, the acoustic chronograph does not have to be setup as close to the path of the bullet, you probably will not shoot a chronograph that is 3 feet below the path of the bullet.

I have thought about mounting an accelerometer on the barrel of the gun and on the acoustic chrony so I could get an estimate of the mis-alignmnet between the two and the use the angle when calculating the velocity. Accelerometers are cheap, almost free, but they tend to drift and the drift may cause as much error as the original misalignment. Alternatively, you could mount a cheap scope on the acoustic chrony use it to point at the same target as you are shooting. Parallax error would be minimal if the target was at reasonable ranges. My chrony is mounted on a piece of extruded aluminum so it lends itself better to a scope than the two box solution but the latter is more convenient.

Probably more than anyone, besides a pointy-head, would vere want to know about acoustic chronys but thought I would share the ideas if someone wanted to explore them.

 

[PracticalTactical]

One issue acoustic chronys have that optical ones do not is that to get accurate muzzle velocities you need the microphones to be carefully aligned with the axis of the barrel. The speed of light is so much faster than the speed of sound so the alignment is not as critical.

I designed and built a couple of chronys that use microphones about 10-12 years back and use them for load development to find loads that have low standard and extreme deviation. Before I built the acoustic chrony I worked up the math to understand where the errors were and I found them critical to alignment, if you want an accurate measurement of the muzzle velocity the alignment is critical, when developing loads a rough estimate of the muzzle velocity is not as critical as the spread.

The beauty of using microphones instead of non-illuminated optical sensors is the position of the sun or clouds do not impact your measurement. In addition, the acoustic chronograph does not have to be setup as close to the path of the bullet, you probably will not shoot a chronograph that is 3 feet below the path of the bullet.

I have thought about mounting an accelerometer on the barrel of the gun and on the acoustic chrony so I could get an estimate of the mis-alignmnet between the two and the use the angle when calculating the velocity. Accelerometers are cheap, almost free, but they tend to drift and the drift may cause as much error as the original misalignment. Alternatively, you could mount a cheap scope on the acoustic chrony use it to point at the same target as you are shooting. Parallax error would be minimal if the target was at reasonable ranges. My chrony is mounted on a piece of extruded aluminum so it lends itself better to a scope than the two box solution but the latter is more convenient.

Probably more than anyone, besides a pointy-head, would vere want to know about acoustic chronys but thought I would share the ideas if someone wanted to explore them.

I would think that the distance between the bullet and each microphone could significantly offset the reported speed, but perhaps the longer distance between the microphones would provide a more accurate indication of shot to shot velocity spread.

A downside might be that if the round is sub sonic, it might not register.

 

[wwbrown]

I would think that the distance between the bullet and each microphone could significantly offset the reported speed, but perhaps the longer distance between the microphones would provide a more accurate indication of shot to shot velocity spread.

A downside might be that if the round is sub sonic, it might not register.

Subsonics will not work the microphones would trigger on the muzzle blast and the speed reported would simply be the speed of sound.

I have thought about a quick repurposing of my acoustic chrony where the mics are ditched and replaced with accelerometers (sensors that measure shock, kind of) and place the accelerometers on 2 pieces of thin cardboard. Mount the cardboard rigidly parallel to each other and place it in the path of the bullet. This might provide a means to directly and accurately measure the velocity say at the target at 1,000 meters. One possible issue is how much the thin cardboard on the first sheet will slow the bullet down. If the accelerometers get shot they can be replaced for a buck or two.

Just some random thoughts,
wade