Alright everyone! Welcome back to Cody's Lab.
So I just picked up a little $40 pellet gun from the store
and apparently this little guy can shoot pellets at 715 feet per second.
So today I'm going to use my new chronograph and test that out.
And also, something I've always wanted to try
is to see how fast it shoots when I've replaced the air
with Helium.
So I'm going to be shooting lead pellets through this gun
They weight about half a gram each.
I'm also going to be shooting indoors
because the weather outside is not exactly great.
Also, I'm going to be pumping the gun 10 times for each shot
That way we've got a standard and that is the maximum for this gun.
I'm going to shoot 4 shots with each
That way we can get sort of a statistical average
So here we go
Shooting the pure air
3, 2, 1
Chronograph didn't pick it up.
We're going to have to fix the lighting.
OK so we switched to using incandescent lights
because the fluorescent lights were not working with the chronograph.
So, I've replaced the ring with paper, so lets fire this.
Just air, 10 pumps.
3, 2, 1
Alright, and we have a number.
625 feet per second
So this is quite a bit lower than the speed that the gun says in the instructions
But that could be because of altitude or variations in the gun type.
Let's run a few more bullets through it so we get an average.
So I've added this plastic bag covering the gun.
This way I can make the atmosphere around the gun Helium
That way when I pump it, I'll be pumping in Helium
So, lets see if this holds
I've already tried it with air, so it aughta hold
OK, there we go.
Atmosphere of mostly Helium
There's going to be a little bit of oxygen in there
But if this speeds up the bullet then we'll know it's becasue of the Helium.
Alright, lets set up that other camera.
Let's see if I can pump this still
And load the pellet.
Yup, looks good.
Make sure I can still pump it.
Kinda awkward
there we go
one
two
three
four
five
six
seven
eight
nine
ten
all right here we go
Helium atmosphere 10 pumps firing in 3 2 1
sounded different
think the velocity is higher
not by as much as I thought it might be but it's a number
let's try this a few more times
Wow actually increased a lot
that's just 10 right?
How much is it?
733
I think I know what's going on here
so after each shot
I've been giving it a little bit of extra helium just take into account any
diffusion of air into the bag or anything like that
and that seems that these velocity of the shells are actually increasing
slightly I must be because there's becoming a greater percentage of helium
in here
that's kind of an interesting thing
so here's the velocity numbers for the air and here is for the helium
here's the average for the helium an average from the air you can see the
helium is quite a bit more than the air was in fact I worked it out and the
energy from the helium was 11.5 joules and from the air
9.1 on average with the max on the helium being 12.5 the max on the air
being 9.4 i have to admit that's not a big difference as I thought it would be
but it is still significant
so now comes the part where I try to explain how this all works so here's the
gun
here's the gas molecules under pressure now to show their velocity
let's add tails to them their average velocity is the speed of sound
if this is air molecules it's about 1,100 feet per second
now add a bullet to open the pressure chamber so that the gas can escape the
gas molecules which are bouncing around like little rubber balls bounce off the
bullet imparting a little bit of momentum to it each time
now when the bullet is farther down the barrel
it's moving very quickly in the case of the pellet gun about 600 feet per second
which means the slower gas molecules have trouble catching up to the bullet
helium because the gas particle has a lower mass but the same energy
it's moving faster which means the helium molecule can catch up to the bullet
and still impart its momentum
even with the bullet moving in a high speed
this is of course how a light gas gun works
except the light gas gun uses much higher pressure, heats up the gas, and use helium to drive the projectile through a very long barrel
achieving speeds that are near orbital velocity just crazy and i hope to build
one of those someday but until then see you next time
yeah