An M1A1 with its bulge showing
I’m going to venture onto engineered’sTM®©µʘѾ2 turf for just a moment, and talk about a piece of modern weaponry. With luck, I won’t have my tires shot out after our next staff meeting. Maybe I’ll bring cookies.
For a long time, I’ve wondered what the purpose of bulging appurtenance on the M1A1’s M256 main gun barrel. It looks like some sort of expansion chamber, but I couldn’t figure out why they would need one. In fact, you would think it would be counter-productive, in that it would rob the projectile of some of its velocity, although not by much. I made a mental note to research the gun or ask someone about it, then promptly forgot about it until the next time I saw the thing. Thus, many years passed…
The Rheinmetall 120mm L44
Lo and behold, I finally remembered about it the other day, and looked it up on the net. It turns out to be a very elegant solution for a problem that I had no idea existed, which is gun smoke accumulating in the gun turret via the breech and choking the tank crew and possibly causing an explosion.
The device is called a bore evacuator, and it uses the gas pressure from a fired round to force the smoke remaining in the barrel of the gun to vent out of the muzzle, rather than the breech. The way it works is, (quoting from the Wiki)
“As the shell passes through, an opening into the bore takes in the gases, containing them until the shell has exited, then releases them back into the barrel. The openings are angled toward the muzzle, so the stream of still fairly high pressure gas drags both combustion gas in the barrel and fresh air from the open breech toward the muzzle. This reduces the chances of these explosive propellants flowing backwards into the turret, causing combustion as they mingle with oxygen.”
Also, the bore evacuators are made from glass reinforced plastic, which I thought was somewhat unusual.
But isn’t that an absolutely lovely piece of engineering? So simple and elegant.
So I’ve learned something new, and perhaps so have you. Except for the ex-tankers (tank jockeys? What is the proper term?) and the usual crowd of weapons zealots, of course. I’m sure that they will fill us in on the details that I’ve missed.
No no no….it is the spot for writing the Tanks name.
<img src="http://i69.photobucket.com/albums/i65/lilwillie_wi/Dan/th_danshootiniron.jpg" border="0" alt="Photobucket" >
/Brother was a Tanker. 1st Marines, 1st Division
I stand corrected.
/Thanks
Ok, your reason is much more scientific and accurate. Mine was just cooler.
You said cookies? I like cookies.
Very interesting post, Herr Professor.
Then cookies you shall have. They're much cheaper than Yokohamas.
"Also, the bore evacuators are made from glass reinforced plastic, which I thought was somewhat unusual."
ABS, Nylon and polycarbonate come in glass filled flavors. They are used in places where a lot of stress may occur but metal is either too expensive or too heavy.
For example, the picture below shows two identical parts (they are clamps that hold Logitech driving wheels to a desk, used as cable holders by my cubicle neighbor). The one on the right is ABS, the one on the left is glass filled ABS.
<img src="https://lh5.googleusercontent.com/-ybOCzi8INVs/Trw8GxWOKBI/AAAAAAAACDw/COJP_yyTSgg/s1280/IMAG1125.jpg" width=550>
Thank you for that information, it's great to know these things. The reason I was surprised was because of plastic being used on a gun barrel, where you would think that the pressures involved would be very high, and plastic would be problematic. It just shows a gap in my understanding of how the mechanism works, among other things.
I did talk with my brother and he said it was or is basically fiberglass. Three small holes evacuate the excess gases.
I learned this in Fluid Dynamics class, IIRC…