05-10-2011, 02:11 PM
LR1955 Wrote:...There is a problem in defining a barrier based on a steel of any sort. Barriers are not monolithic (if that is the word to use). For example, we had to stop using RHA plate as a testing material when armor started to become laminates of different types and alloys of things... ...So, you have to decide what is more important -- penetration of hard things or terminal effects on humans.
Gene,
The following expansion is not intended to make the problem of defining terminal performance seem impossible. It is not. The real issue is how one transitions from the anecdotal to the measurable and testable requirements.
As you've indicated, we need to ask ourselves what the bullet needs to do. Yes, living flesh behind barriers (or with no barriers) is one class of terminal effects. What kind of response do we want if the target is a moving vehicle? Or a low-flying helicopter? Low flying aircraft?
These and more represent the kind of engagements we know that folks using small arms get into. How important is one or another. I can surmise the pucker factor gets significant when one is trying to stop a bomb-laden truck with an inadequate cartridge.
But, what does the bullet need to do to stop that truck?
- Kill the driver?
- Kill the engine or power train?
- Deflagrate or detonate the bomb?
Make sure the design target results in a weapon that will pass the Admiral's test. Yes there are examples of the failures. Usually attributable to an overenthusiastic PM pushing the design requirements down to the absolute minimum. "Absolute minimum" performance specifications makes the design vulnerable to multiple minor oversights. On the other hand, going to an overly robust design spec makes the ensuing device too heavy, costly, or unwieldy to be adopted.
In having designed or worked with more design targets in various applications in the intervening years, I have learned the importance of keeping the design target simple enough to allow repeatable fabrication and testing.
An example of unintentional violation of the simplicity rule occurs when one specifies "X mm penetration in ballistic gel after perforating a truck door frame." The hiccup occurs when you actually use the door frame in developmental testing, one can be led astray by the inevitable interaction with the things that are inside the door frame.
So the apparently obvious solution is to replace the door frame with sheets of door frame material with the appropriate air gap. This makes an incomplete statement, because one needs to also specify the frequency the bullet is likely to encounter something besides air in the space between the exterior and interior sheets. We likely need to make this statement rather than requiring that the bullet pass through the braces, fasteners, door latches, window cranks and gears, etc. The added requirement would likely make the bullet way too big for normal infantry applications.
Next, one needs to state the obliquity at which the bullet must be able to attain the specified penetration into the ballistic gel, or engine block, etc. behind the "door frame." Oops! the increased angle means that the interior stuff gets hit more often. How often?
Aw heck, the off-angle impact makes my bullet start to tumble and the increased travel time makes the bullet turn enough that it won't penetrate the second sheet.
And so on...
If you've gotten this far in the note, its time to take a step back and recognize that your request is absolutely on track. We need to specify more than one target and assign relative importance. My caution is that the transition from truck-stopping, armored bad guy incapacitation, etc. to testable targets is not a trivial step.
Cheers!
Joe