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Old December 19, 2012, 05:46 AM   #1
Doc Hoy
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Ballistics smart guys....Do I remember....

....seeing a graph of the pressure in a barrel upon discharge? I am speaking of a graph for black powder.

Not certain why I want to see this again (if I ever saw it before.) but as I am beginning to load this 45-70 BPCR round, it seems as though at least a casual understanding of barrel pressure is important.

I am not so concerned about barrel failure. I am loading light at 50 grains for now. I just want to know about pressure in the barrel for this big round.
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Old December 19, 2012, 07:11 AM   #2
Doc Hoy
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I have found...

...A chart which shows what appears to be a good comparison between pressure over time from BP versus pressure over time for smokeless.

I see four things:

1. BP begins to develop pressure more quickly than smokeless.

2. Smokeless rises to its maximum at almost exactly the same time as BP rises to its max.

3. Smokeless develops twice as much maximum pressure.

4. BP pressure declines more slowly than smokeless.

I do not know how the volumes or weights of powder were decided upon for this chart. I don't know the length of the barrel (except for the fact that the bullet exited the barrel after 1.1 millisecond in both tests, which may inform us as to how the charge was decided upon.) I don't know the characteristics of the projectile.

I also saw a chart which implied that a 45-70 with BP develops 25000 PSI.
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Old December 19, 2012, 02:25 PM   #3
woodnbow
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I seem to remember a chart like that in the old Dixie Gun Works catalog. Old as in the '70's or so. It might also have been printed in one of Sam Fadala's handbooks as well.
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Old December 19, 2012, 02:42 PM   #4
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I am not sure where mine is right now,but you might try the SPG bullet lube booklet.Great little resource on BPCR loads.

Not to be nosy,but I do hope you understand the correct charge of black powder is the amount that totally fills all air space under the bullet.In smokeless,its OK to back off and load 88% loads density.Not so with black!

You select a bullet,one way or another,decide a seating depth.Your correct charge is not an arbitrary conservative number,with the correct charge the bullet base rests on the powder,or whatever card wad,grease cookie,etc,.
No air space!

Have fun.
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Old December 19, 2012, 03:15 PM   #5
Doc Hoy
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HiBC...

I'll look up the SPG book. I saw excerpts from it on the internet but not the entire thing yet.

Think I remember it being about thirty bucks on Amazon.

I am loading light and then using a card and cornmeal to fill the air space.
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Old December 19, 2012, 04:42 PM   #6
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I found one online somewhere & posted it on one of the B/P specialty forums a while back.

If I could only remember which one?
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