Optimal Barrel Time - Shockwave measurement?

[David Bookstaber]

Has anybody successfully measured barrel shockwaves that correspond to Chris Long's OBT theory?

The reason I ask is that I would like to extend the theory to barrels wearing muzzle devices. I assume that there is no practical analytic way to predict how a muzzle device -- which may be of different materials than barrel steel, and which may provide longitudinal damping -- will affect the shockwaves. But if it is possible I would sure like to try to measure the effect!

 

[necchi]

Varment Al's page has some great stuff,
http://www.varmintal.net/atune.htm
that's just one section,,check out his other info..

 

[David Bookstaber]

Varmint Al shows some impressive and interesting work! But everything I read there was simulated. I'm wondering if somebody has built a sensor system to measure the pressure waves in a real-life firing gun?

 

[Tozguy]

Just in case this might relate to your question, Harold Vaughn did some testing on muzzle blast, bullet canting, muzzle blast reduction and crowning. His findings are reported in Chapter 7 of his book RIFLE ACCURACY FACTS. He measured muzzle blast pressure using strain gauges. He explains the physics involved with muzzle blasts and shows some shadowgraph pictures of actual muzzle blasts and its components at different stages in time. Notably he designed and tested a muzzle ventilator in order to determine how reduced blast pressure might improve accuracy. Hope this helps. Good luck!

 

[Steve Blair]

The software that Al primarily uses is LS-Dyna, based upon the earlier, Lawrence Livermore developed LL-Dyna. It is very well-validated software whose simulations have been proven many times by real-world testing. My employer is one of the earliest users of LL-Dyna, holds a source code license for it and has contributed many features to the core code. Properly used, it can accurately characterize physical events from explosions to structural deformation under dynamic load. Al is an experienced analyst and his results likely valid.

Performing actual measurement is somewhat of a problem. Any physical barrel contact will change the event, perhaps enough to undermine the result. A Laser Interferometer (link) is one way to obtain accurate measurement without physical contact. If you are in a fortunate financial position, many firearms enthusiasts would appreciate the underwriting of such an effort, which is likely to be expensive.

 

[David Bookstaber]

I am denigrating neither Al's work nor the power of finite element analysis. However accurately characterizing a muzzle brake or baffle suppressor for finite element analysis is not something anybody is going to spend the time or money doing.

The replies so far suggest there might be some confusion regarding OBT theory, so if in doubt please see the various papers on the subject available here. I am referring to longitudinal "acoustic" shockwaves that affect muzzle size, not harmonic vibrations that primarily affect muzzle direction. If Long's theory is correct then there is a very strong pressure wave that should be picked up with a pressure transducer, and given the magnitude and nature of the pressure wave a transducer will not "change the event."

My original question, restated, is whether anyone has tried to measure the OBT pressure waves. If measurement was attempted, what equipment was used -- in particular, what sample frequency and sensitivity ranges were used? If pressure wave detection failed was it because there is too much noise in the firing event, or is there some other hypothesis? If it succeeded then what would the minimum level of equipment likely be to reliably make such measurements?

 

[Steve Blair]

A huge amount of testing as you describe was performed at APG BRL, but not in relation to OBT theory. I have several pressure gradients derived from caliber .50 barrels from testing done in the seventies and eighties. These were done the old-fashioned way with crushers.

RSI offers their PressureTrace with very lightweight transducers, but it appears that it does not support multiple, simultaneous channels. Their software does advertise OBT calcs.

 

[243Mendoza]

Has anybody successfully measured barrel shockwaves that correspond to Chris Long's OBT theory?

The reason I ask is that I would like to extend the theory to barrels wearing muzzle devices. I assume that there is no practical analytic way to predict how a muzzle device -- which may be of different materials than barrel steel, and which may provide longitudinal damping -- will affect the shockwaves. But if it is possible I would sure like to try to measure the effect!

Note sure what is OBT theory is but I remember reading a AIAA paper (American Institute of Aerospace and Aeronautics) back in the 90's about the theory and experiment of a circumferential wave travelling down a barrel (the analogy is that of a snake swallowing its prey). The authors were students of a university in Alabama, I think.

 

[David Bookstaber]

Note sure what is OBT theory is but I remember reading a AIAA paper (American Institute of Aerospace and Aeronautics) back in the 90's about the theory and experiment of a circumferential wave travelling down a barrel (the analogy is that of a snake swallowing its prey). The authors were students of a university in Alabama, I think.

That's exactly the basis of OBT theory: Trying to ensure that wave isn't expanding the muzzle at the moment the bullet exits. It would be awesome if you could find that paper and post a copy!

 

[TonyR]

I think that this is what you are looking for:
http://www.the-long-family.com/OBT_paper.htm