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Normal Topic BP, BN, & pressure (Read 1555 times)
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BP, BN, & pressure
Oct 23rd, 2009 at 2:37pm
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With smokeless, the consensus seems to be there's little pressure difference between bottleneck and straight cases so long as the net case capacity is the same. How about with black powder?

In my notes is this by Venturino:

All of those were bottleneck shaped cases, and by the mid-1870s, it had become evident that straight cases gave better results with black powder as propellant. This change in case shape was probably spurred by the U.S. government’s testing of various case shapes in developing the .45-70 prior to 1873. Its testing showed that with all things equal, straight cases gave essentially the same velocities but at considerably lower pressures.

Does anyone know of other references--or even just opinions--on this topic? I'm curious about that considerably lower part.

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Re: BP, BN, & pressure
Reply #1 - Oct 23rd, 2009 at 5:19pm
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Well - there's some:  Only the US had a straight-cased BP cartridge, whereas all of the major military powers of the day (UK, France, Germany) used BN rounds.  Mind you, there is a good reason for using BN rounds with high-powered BP cartridges:  straight cases tend to become too fragile as too long, they bend or get damaged more easily, making them harder to chamber.  Cartridge length especially is an issue with repeating rifles (yes, there were issue military BP repeating rifles - maybe not in the US, but...). 
However, there's also another equation: more pressure usually means higher MV - just look at the Last Mauser BP round, and the MV developed...

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