Other than the academic interest, I see little value to this type of discussion, in the context of wondering if it's okay to put a wad against the powder.  It is absolutely not okay to do so, we know very definitely that doing so will have a high probability of causing a ring to occur.  Your initial post stated that you were doing this known ring causing practice, and you stated that you were somewhat new to this type of loading/shooting.  It is very good for those that are more experienced to offer cautions to new shooters on unsafe practices, which is what happened in this thread. 

Now, the analysis of why a ring occurs, and trying to figure out the mechanism, that's a pretty valid, although somewhat academic discussion.  In the context of "I know that a probability of ringing a chamber exists by using a wad on the powder, let's explore why that happens".  Not in the context of "I and my friends just started shooting and we're putting a wad on the powder and I haven't rung my chamber, so maybe it's okay to do so and the research to date just isn't good enough."

However, we live in a culture where we allow people to make their own mistakes, and learn from them, if they wish.  We're not going to stop you from putting a wad on your powder, but we're sure going to inform others that you are encouraging to do the same that there are risks to doing so.  It's all right to make your own mistakes or do your own experiments, but it's useful to inform others of the risks, so they can make an informed decision on whether they also want to take risks or do experiments.

This falls under the category of a type III learner.*

*
type I - learns by reading or hearing about others experiences
type 2 - learns by watching others experiences.   
type 3 - Has to go out and pee on the electric fence himself.

From my experiences messing with wads and other various powder placers the problem lies in the quality of steel used to make the barrels. The old French scientist that perfected smokeless back in the day stated a wad over the powder could increase the pressures at the base of the bullet two to to three times so with that thought in mind my loads are kept below 20,000psi in barrels that will withstand 60,000psi when using a wad. That said, no Eye Towel Yan guns, antiques of any kind or barrels made from suspect steels; modern ordinance steels only! Works for me, YMMV.

No, I don't piss on electric fences but have and will continue to straddle one to get to the other side, lol.

Studies of Shock Wave Reflections and Interactions (Paul Vieille Lecture)

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- the primary focus has been investigation of the behaviour of gas dynamic shock waves expanding on Paul Vieille's knowledge.

THX MartiniBelgian for the direction to more info.

problem to be solved in the 17th century.
1 Introduction
Material properties, an equation of state for the material, and conservation equations
for mass, momentum and energy are required for the mathematical description of
the propagation of blast and shock waves. This was not set up at once, but took a
long way over several centuries. The development of the theory of blast and shock
waves is chronologically described in the following sections.
Torsten D¨oge
Dr. Linse Ingenieure GmbH, Karlstr. 46, 80333 Munich, Germany
e-mail: doege@drlinse.de
Norbert Gebbeken
Institute of Engineering Mechanics and Structural Mechanics, University of the Bundeswehr
Munich, Werner-Heisenber-Weg 39, 85577 Neubiberg, Germany
e-mail: norbert.gebbeken@unibw.de
E. Stein (ed.), The History of Theoretical, Material and Computational Mechanics, 249
Lecture Notes in Applied Mathematics and Mechanics 1,
DOI: 10.1007/978-3-642-39905-3_15, c Springer-Verlag Berlin Heidelberg 2014
250 T. D¨oge and N. Gebbeken
The content of this chapter was collected when writing the dissertation [11]. Only
by reading the original literature it becomes clear, what problems had to be solved,
why problems were not solved until a certain time and why some problems were
then independently solved by several persons. The authors of this chapter recommend to everyone to obtain and read the original literature. It is very instructive!
2 The 17th Century
MARIN MERSENNE (1588–1648) measured around 1636 the speed of sound (LENIHAN [34, 35]). He applied two methods. One method was to measure the time from
the arrival of the flash of a canon, which distance was known, until the arrival of
the report of the canon. With this method, he determined the speed of sound to 230
Toisen per second (≈ 448m/s) [34]. The second method was to measure the time
that a sound and its echo took to a wall and back. With this method he determined
approximately 316 m/s [35].
GALILEO GALILEI (1564–1642) wrote already in his 1638 published work Discorsi e dimostrazioni matematiche intorno a due nuove scienze attenenti alla meccanica et i movimenti locali about experiments on air. Thereby, he described an
experiment, with which the density of air can be determined [22, p. 117–118]:

Short version, no.  It is not a requirement,  but can be beneficial for accuracy and fouling.   Even the airspace thing is relative,  not absolute.