Re: OT: Repeatably lobbing "projectiles"

On 11/24/2024 7:36 AM, Liz Tuddenham wrote:

Don Y <blockedofcourse@foo.invalid> wrote:
 
[...]

Couldn't the plunger be "polystyrene cup shaped" so it stays behind
for reuse, automatically?

 
No - because the cup has to be in contact with the projectile to
maintain its shape while it is accelerated up the barrel.  That means
the air pressure must be behind the cup.

 
I don't understand.  What's the difference between the cup BEING
the top of the plunger (which has air pressure behind it) and
leaving the barrel WITH the projectile?