Re: [Phys-l] Ballistics divertissement

[Dan MacIsaac <danmacisaac@mac.com>]

> On Oct 6, 2006, at 1:49 PM, Roger Haar wrote:
> Hi,
>
> 	I believe my friends who are into guns have said things to imply  
> that a
> blank would feel different then a bullet.  The problem is  
> complicated by
> things like the burn rate of the powder . . .  But I think the  
> simplest
> model is the that if the shells are loaded with the same amount of
> powder, there would be equal amounts of energy.

The feeling can be VERY different.  In the Cdn army as a young  
officer / nascent storm trooper, I fired a pretty "heavy" assault  
rifle - the .308 or 7.62mm FNC1 rifle.  On exercise we fired blank  
cartridges with a fitting attached to the end of the rifle muzzle  
clipped to the bayonet stud called a blank firing adaptor or BFA.   
The BFA constrained blank cartridge gases sufficiently that enough  
were diverted into the gas cylinder to operated the auto-loading  
mechanism (cycled the action) via a cylinder and piston mounted over  
the barrel and ported to the barrel partway down. Ordinarily the  
bullet constrains those gases sufficiently while moving down the barrel.

<http://www.canadiansoldiers.com/mediawiki-1.5.5/index.php? 
title=Infantry_Section>

Blanks fired with the BFA  were barely able to cycle the rifle  
action, and blanks could be comfortably fired from the hip with a  
long slow easily managed recoil.  The blast leakage would shatter  
glass or smear insects into paste near the muzzle.

When fired with live rounds on the range, the rifle was a bruiser --  
when fired by qualified marksmen it literally left a bruise on your  
shoulder after a full day at the range (flinching and anticipating  
the rifle stock impact were serious training concerns in  
marksmanship).  The feeling was quite hammer-like, and recruits who  
didn't have their cheek correctly positioned along the stock were  
readily identifiable by facial bruising.   The automatic (Squad  
Automatic Weapon) C2 variant of the rifle had a truly gruesome recoil  
and was not for smaller lightweight men like myself who could  
actually be driven off the firing line mound at the rifle range from  
the prone position (we were allowed to range qualify with a loader  
hanging onto the bipod to keep us on the mound).

There is a BIG different in recoil with live rounds and blanks, even  
with blanks designed to produce additional gases adequate to cycle  
the action of gas operated firearms.  I also found significant  
differences firing live rounds and blanks from the 9mm Browning Hi  
Power pistol and 9mm Sterling Submachine Gun (SMG) as well.  Probably  
this is not an issue with a small calibre rifle like a .22

<http://www.nisat.org/weapons%20pages%20linked/United%20Kingdom/ 
sterling_9mm_l2a3_sub.htm>
<http://en.wikipedia.org/wiki/Browning_Hi-Power>

Man,  when I googled SMGs I found a gold-plated deactivated Sterling  
SMG in a mahogany case.  Pretty spooky; I used to live in that world.  
I have to look up some old friends :^).

Dan MacIsaac, Associate Professor of Physics, SUNY-Buffalo State College
222SciBldg BSC, 1300 Elmwood Ave, Buffalo NY 14222 USA 716-878-3802
<macisadl@buffalostate.edu>  <http://PhysicsEd.BuffaloState.edu>