On Fri, Jul 10, 2015 at 1:24 PM, W. Hopper <whopper@pobox.com> wrote:

A tapered bore offered a way to build up chamber pressure and increase velocity with the slower-burning powders of the day.  We no longer use tapered bores because our modern propellants burn about as fast as is possible for a chemical explosion, and anything that reduces their speed of expansion, such as muzzle friction, reduces muzzle velocity.  

Kurt was originally seeking a way to model the main guns of the reimagined Battlestar Galactica in Traveller terms, yet still remain true to both the rules published by Margaret Weiss Productions (and presumably based upon the technological specifications of the show's science consultants) and as shown in images of the guns as these appear in the actual episodes. My insertion of tapered bores into the discussion was made in an effort to do so.

 

This is why smoothbore cannon are now back in vogue, because they produce higher velocities.

But smoothbore cannon wouldn't have much accuracy at all over WWII naval (let alone Traveller space) engagement ranges, which seems to be about what we're looking at with the Galactica. While there are no crosswinds in space, there is also no atmosphere for the submunition stabilizing fins to grab. And based on the location of the Ragnar anchorage, the Galactica would expect to at least occasionally engage in atmospheric combat. 

 

In an age of electro-magnetic propulsion such a rail guns . . .

But the visible rails on these "rail guns" are only some 8 meters long (scaling from the CGI spacesuits seen through the turret canopies). So they can only exist to provide guidance and secondary boost. So they can't reasonably be the primary propulsion source, unless the tech behind them is SERIOUSLY out of proportion with that of the rest of the show. Except for the "magic teleport" stardrives and the apparent plasma rocket thrusters, the rest of the tech seems barely more advanced (if at all) over what we have today.

 

, there is no such thing as chamber pressure and anything that reduces muzzle velocity is a Bad Thing.  Tapered bores are a relic of the past, and have no place in the far future, again IMHO, except on lower-tech worlds.  

Now that I type that, I remember . . . that the locals had 25mm or so squeeze-bore rifles that could punch through BD if they rolled well enough.

David Drake uses both tapered bore rifles and cannon in his one-off novel Forlorn Hope. From page 16 of that work:

"The cannon had a single barrel which was a trifle over three meters long. The bore at the muzzle was seven millimeters. Through it blasted a five hundred milligram osmium pencil which had with it's sabot a diameter of twenty millimeters when it was slammed into the breech."

A Vietnam War veteran, Drake would have been familiar with the limitations of the XM-81 gun/launcher mounted by the Sheridan light . . . so he went "back in time" to the tapered bore concept on purpose.