Measuring Bullet Speed

[Fat Crack Ho]

I'm toying with the idea of building a chronometer for measuring bullet speed.
Just want to get some opinions on the best type of sensors to use.

My basic idea was to have two sensors a fixed distance apart (1m for arguments
sake). When the bullet pass through the first sensor, zero a timer. When it
pass the second sensor, read the timer, work out speed.

thanks.

 

[Rod Speed]

I'm toying with the idea of building a chronometer for measuring bullet
speed. Just want to get some opinions on the best type of sensors to use.

My basic idea was to have two sensors a fixed distance apart (1m for
arguments sake). When the bullet pass through the first sensor, zero
a timer. When it pass the second sensor, read the timer, work out speed.

They're buyable. From memory they use an optical beam system.

I can find out if you like from someone who uses them.

They're basically used to calibrate bullet loads etc.

 

[Mr Anish Varsani]

That's what I need one for. They run for about $300. The one's I've seen are a
bulky unit. I wanted to make something a bit less bulky. If I can use
inductive type sensors, it would be pretty easy to build the thing. If I have
to use optics, I may as well buy one already made.

 

[Mike Harding]

That's what I need one for. They run for about $300. The one's I've seen are a
bulky unit. I wanted to make something a bit less bulky. If I can use
inductive type sensors, it would be pretty easy to build the thing. If I have
to use optics, I may as well buy one already made.

There is a technique (I have a copy of the patent somewhere)
which uses a flat bar laying on the ground with a few sound
sensors (microphones?) along it's length to triangulate the
location of the projectile as it passes over the bar. Two of
those spaced a know distance apart could be used to
determine velocity. Or one of them a known distance from
the firearm?

What about a vibration sensor on the target (at say, 100m
from the shooter) and a timer triggered by a sound sensor
close to the firearm and stopped by the vibration sensor?

I'd be a bit dubious about inductive measurement although
I suppose if you put the firearm in a bench rest and had
the sensors close to the barrel you could avoid shooting
them

What sort of shooting are you doing?

Mike Harding

 

[John]

Mike,
Do you have the patent number handy for
the system you described. I have been thinking
about using audio for bullet detection for a while and
am interested in any info that is available.


John

 

[Mike Harding]

Do you have the patent number handy for
the system you described. I have been thinking
about using audio for bullet detection for a while and
am interested in any info that is available.

Sorry but no - I'll keep on checking though - I'm sure it's
_somewhere_!

In the meantime try a search on the US patent site:
http://www.uspto.gov/

which was where I found it. The system is still in use
by the Australian Army on some of their firing ranges.

Mike Harding

 

[John Harvey]

I'm toying with the idea of building a chronometer for measuring bullet speed.
Just want to get some opinions on the best type of sensors to use.

My basic idea was to have two sensors a fixed distance apart (1m for arguments
sake). When the bullet pass through the first sensor, zero a timer. When it
pass the second sensor, read the timer, work out speed.

There's a dead simple way which uses a pendulum with two sheets of
paper attached. Knowing the period of the pendulum and the distance
between the sheets of paper you can calculate the velocity from the
relative displacement between the entry and exit holes.

Dunno what sort of accuracy you can reasonably expect but I think this
was the historical chronograph used in the days before sensors.

 

[Phil Allison]

There's a dead simple way which uses a pendulum with two sheets of
paper attached. Knowing the period of the pendulum and the distance
between the sheets of paper you can calculate the velocity from the
relative displacement between the entry and exit holes.

** Hmmmm, a 303 cal rifle bullet exits the barrel at around 1000 m/S.

If the paper moves at say 500mm/S and the two sheets are say 1 m
apart then the displacement of two ( probably ragged ) holes will be 0.5mm.

Dunno what sort of accuracy you can reasonably expect ....

** SFA.



............. Phil

 

[Fat Crack Ho]

Shooting from a bench mainly. I shoot .223 and 30-06 out to 500 yards. I
wouldn't bother with a chrono for handgun loads unless shooting metal plate, in
which case power factor would be a nice thing to know.

 

[Mike Harding]

Shooting from a bench mainly. I shoot .223 and 30-06 out to 500 yards. I
wouldn't bother with a chrono for handgun loads unless shooting metal plate, in
which case power factor would be a nice thing to know.

Go for my suggestion above. A vibration switch to an 8 pin
PIC which sends a signal via an LIPD Tx to an Rx at the
shooters position which stops the counter which was started
by the "bang" At 500 yards it will take the projectile about
0.5 sec - plenty of time for the electronics to return pretty
good accuracy I imagine - hmmmm.... do I see a possible
product here???

Mike Harding

 

[Phil Allison]

At 500 yards it will take the projectile about
0.5 sec - plenty of time for the electronics to return pretty
good accuracy I imagine - hmmmm.... do I see a possible
product here???

** At 500 yards ( metres? ) the mussel velocity would have dropped by
about half.

Eg. WW2 Spitfires etc used 8 x Browning 303 cal machine guns with 3000
fps mussel velocity, all harmonised to converge at 200 yards or so -
beyond that range the projectiles were rather non effective.





............. Phil

 

[Mike Harding]

** At 500 yards ( metres? ) the mussel velocity would have dropped by
about half.

That's true, it would. So measurements would be comparative
or an average which would probably be OK for the purpose
of tuning powder loads I guess?

Eg. WW2 Spitfires etc used 8 x Browning 303 cal machine guns with 3000
fps mussel velocity, all harmonised to converge at 200 yards or so -
beyond that range the projectiles were rather non effective.

Interesting. 600m is a standard target range for the forces using
5.56mm and I gotta tell you... you wound _NOT_ want to be
standing 201m in front of my .303

Perhaps the combined speed of the aircraft meant that shooting
at anything much more than 200m away was useless?

Mike Harding

 

[Phil Allison]

That's true, it would. So measurements would be comparative
or an average which would probably be OK for the purpose
of tuning powder loads I guess?


Interesting. 600m is a standard target range for the forces using
5.56mm

** On what planet ?



and I gotta tell you... you wound _NOT_ want to be

standing 201m in front of my .303

** That is about were the Browning's projectiles converged.

Perhaps the combined speed of the aircraft meant that shooting
at anything much more than 200m away was useless?

** The relative speed was normally very small - depending on whether
another figher or a bomber was the target.


BTW

Another very simple way to measure mussel velocity is to use momentum -
which is always conserved. Fire the round into say a bag of wet sand -
the "mv" of the projectile will equal the "mv" of the sand bag after
impact. You know the two "m" s and if the sand bag is also a pendulum
then simple maths applied to the deflection gets you close.




........... Phil

 

[Philip Terrill]

** On what planet ?



and I gotta tell you... you wound _NOT_ want to be


** That is about were the Browning's projectiles converged.






** The relative speed was normally very small - depending on whether
another figher or a bomber was the target.

The relative speed of the aircraft to the target may be small, but the speed
of the bullet relative to the air would be exeptionally high- and this
increase in velocity would have a really, REALLY big effect on the wind
resistance (and hence the de-acceleration) of the bullet (I THINK that air
resistance is proportional to velocity squared).

Hence a change in the bullets relative velocity from 1000ms-1 to say 1200
ms-1 would make a big difference to the bullets slowing down.

cheers,

Phil T

 

[Phil Allison]

The relative speed of the aircraft to the target may be small, but the speed
of the bullet relative to the air would be exeptionally high-

** Nonsense.

and this increase in velocity would have a really, REALLY big effect on
the wind

resistance (and hence the de-acceleration) of the bullet

** Drivel.


(I THINK that air

resistance is proportional to velocity squared).

Hence a change in the bullets relative velocity from 1000ms-1 to say 1200
ms-1 would make a big difference to the bullets slowing down.

** Air to air combat mostly involved speeds of around 250 mph or 110 m/S

BTW The air gunner on a bomber had the reverse ( small ) effect.




............. Phil

 

[Philip Terrill]

** Nonsense.

and this increase in velocity would have a really, REALLY big effect on
the wind

** Drivel.


(I THINK that air



** Air to air combat mostly involved speeds of around 250 mph or 110

m/S


OK, Assuming shooting foward, while flying at 100m/s,

Velocity of bullet relative to ground=1100m/s
force due to wind resistance, and hence acceleration (F=MA) is proportional
to 1100^2=1210000

Force on a bullet fired from a stationary position is proportional to
1000^2=1000000.

From that, the de-acceleration fired from an aircraft is 20% higher (at the
instant it is fired) than when fired from the ground- Which as you say will
make a big difference in the loss of speed over a few hundred metres.

 

[Rob]

Mike,
Do you have the patent number handy for
the system you described. I have been thinking
about using audio for bullet detection for a while and
am interested in any info that is available.


John

John - it may not be relevant but around 1995 National Instruments had an
app. note demonstrating the use of their data acquisition h/w & Labview
software to sense / detect gunshots. I think it was actually used in 'real
life' inner city location to determine approx location of gunshot source.
Details are a little hazy - it was nearly a decade ago that I looked at
it....
rob

 

[Mike Harding]

** On what planet ?

This one.

Mike Harding

 

[Phil Allison]

On Mon, 8 Sep 2003 18:39:28 +1000, "Phil Allison"


This one.

** That begs the question - what planet are you on Mike ?

Everyone here would like to know.




........... Phil

 

[Mike Harding]

** That begs the question - what planet are you on Mike ?

Everyone here would like to know.

A different one to you Phil, I suspect

Mike Harding