Ballistics Question

[Whirligig]

Could a pellet that is being fired from an airgun, say of a spring-piston design, achieve maximum velocity some distance after it leaves the gun's muzzle due to the pellet accelerating to maximum velocity outside of the airgun's barrel?

If so, what are some examples of this phenomenon?

Thanks,

-Whirly

[Roadworthy]

The only way to increase a pellet's velocity after it leaves the barrel is to apply some external force.  Within the barrel that force is obviously the high pressure, high temperature air the piston compressed.  When the pellet exits the barrel this force is no longer acting on it.  I guess it could continue to act for a microsecond or so after the pellet leaves and before the compressed air dissipates.  You may be into hypothetical here.  Of course during this hypothetical microsecond of residual acceleration there is also the air drag attempting to slow the pellet.  That was an interesting question which I can mull over but probably never arrive at a solution on my own.

[Novagun]

Spring guns have a peculiar power delivery in that it occurs in the form of a pulse. A big wallop as the spring advances pushing the piston in front of it. There is some inertia there and it takes a little time for the maximum air pressure to build and then get through the transfer port. Then the pressure  has to overcome the inertia of the pellet and the drag of rifling to send the pellet down the bore. Before the pellet exits the muzzle the piston is rebounding and sucking air back through the transfer port reducing the pressure in the barrel. Even the inertia varies with the mass that the spring is moving.
There is no extra charge behind the pellet as it exits the muzzle to add any accelaration. Just drag all the way from trigger to target.  That is why short barrels are good.
 It is a wonder they work as well as they do but the physics and its laws allow it to happen. It is intertesting to read the laws but the mathematics -- well.
Aren't we lucky it does work.

PCPs are different, they get a push all the way along the barrel.

[Doug Wall]

They only way to do that is to build a rocket engine into the pellet. Like the old Gyrojet guns.

[FPGT72]

Spring guns have a peculiar power delivery in that it occurs in the form of a pulse. A big wallop as the spring advances pushing the piston in front of it.
PCPs are different, they get a push all the way along the barrel.

Hmm....sounds not right...but I don't know anything.

But I would think the propellant delivery would be the same no matter what the power plant, spring, co2, msp, pcp.  You have a valve that will open allow the air in behind the pellet and that air being stuck behind the pellet wants to get out of the barrel....so I think it would be pushing the pellet all the way down the barrel.

There has to be some kind of restriction going on in spring guns to up the pressure....the pistons are say the size of a dime, but a 177 pellet is pretty far from that, so taking the larger volume and smashing it into that smaller area is going to get it moving even that much faster, as well as make a bit of heat, and that is why guns will diesel.

The second the pellet leaves the barrel it is going to start to slow down and start to drop, you can't fool mother nature. 

I am trying to think of a springer that has different barrel lengths, but am coming up empty......I would bet the fps numbers out of a short barrel is lower then out of a long barrel (again to a point....you can make a long enough barrel that a 50bmg would stop moving....it would be a LONG barrel...other factors are at play....the amount of propellant, friction in the barrel for a couple of the biggies.

[rsterne]

No force, no acceleration, after the pellet leaves the muzzle.... The air resistance it meets from the surrounding air must surely be greater than any residual gas exiting the barrel behind it.... unless you are talking a distance of a caliber or so, and there is no practical way of measuring that....

Bob

[Whirligig]

Thanks for all the informative replies!

-W