Welcome! Discussing Airgun Ballistics

AI Thread Summary
The discussion centers on airgun ballistics, specifically the internal ballistics related to compressed air. The initial question addresses whether it's possible to release air through an orifice faster than the speed of sound using only compressed air, with the consensus being that a converging-diverging (CD) nozzle is necessary for achieving supersonic airflow. Additionally, it is noted that if the barrel system were under vacuum, airflow could exceed the speed of sound. The conversation also explores the relationship between pellet exit velocity and airflow, emphasizing that while the air "wants" to move faster than the pellet, it is physically constrained by the pellet's presence in the barrel. The discussion concludes with an affirmation of the importance of understanding these dynamics in airgun performance.
RKT
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Greetings to all Forumites ! I am new to this forum and this is my first post. If the subject of my post does not concur with this section, pls excuse me and redirect me to the correct section. Thanks.

My interest is in ballistics, particularly internal. Most of my questions and discussions will relate to airguns, although I'll discuss the physics here and not mechanical setups. I hope this subject is not taboo.

I should like to start off with this question : Using ONLY compressed air from a reservior, is it possible to let out a stream of air through an orifice faster than the local speed of sound ? I know that a CD nozzle can do it, any other way ?
 
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A CD nozzle is the only way to do it. Anything less will choke.

Well, let me make one caveat...if you were to pull the entire barell system under vacuum, you could pass M1.
 
Re : A CD nozzle is the only way ...

Thanks. That puts me on more conclusive footing. So a CD nozzle is a must.

The next thing I want to know ... Would my following understanding be true ?

' If a pellet exits a barrel at say, 900 fps, then, the airflow must WANT to go way faster than that. The key word here is 'want'. The air actually cannot go any faster than the pellet (as the pellet obstructs the flow) but it WANTS to. Thats pressure. That is to say, if discharged without a pellet, the airflow would be way faster than 900 fps.'
 

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