Thread: Energy/pressure relationship

I was looking at my figures and it got me thinking.
Can energy at muzzle be an indicator of similar pressures?
ie if you had a 140gr pill giving 2500 ftlbs at the muzzle would it be similar pressure to get a 162 delivering 2500 ftlbs at the muzzle (dont get me wrong I use standard pressure signs for assessing my loads this is more just wanting to understand something from a theory perspective)
You would think it would take the same energy input to cause the same potential energy output wouldnt you? (assuming similar bearing surface)

No because it would require a different amount of energy to move a bullet to a particular speed/energy output....
This would be more related to bearing surface of the projectile and the weight of the projectile..

Also the harder the bearing surface the more energy it will require to slide down the barrel I would assume...

Another factor would be burnrate of powder and how fast that energy was spread out onto the projectile... Something like how a fast powder will give you slower speed at the same pressure because it spikes that energy faster before it can get the projectile moving, therefore you lose energy from the pill cause the powder burns up its energy early on when the pills building speed... But in actual fact the same amount of energy was created as if you had used a slower burning powder which would have made the projectile come out the muzzle faster....

Hori,

Try these formulae from John Barsness.
Source: http://www.riflemagazine.com/magazin...20(LO)%202.pdf
They work pretty well and are easy to set up in Excel.

1. Change in bullet weight in the same cartridge: V2/V1 = 0.5 (W1/W2 + 1)
V = velocity
W = bullet weight

2. Change in bore diameter in the same case: V2/V1 = 0.25 [(D2/D1)^2-1] + 1 (e.g. 243Win/260Rem/7mm08/308Win)
V = velocity
D = bore diameter

3. Change in case capacity, same bore size: V2/V1 = 0.25 (C2/C1 - 1) + 1
V = velocity
C = case capacity net of bullet volume

From 1, your 162 grain bullet would be going 93% of the speed of a 140 grain bullet
(e.g. 140grain = 3000fps ==> 162grain = 2796fps)

Originally Posted by Meathunta

Hori,

Try these formulae from John Barsness.
Source: http://www.riflemagazine.com/magazin...20(LO)%202.pdf
They work pretty well and are easy to set up in Excel.

1. Change in bullet weight in the same cartridge: V2/V1 = 0.5 (W1/W2 + 1)
V = velocity
W = bullet weight

2. Change in bore diameter in the same case: V2/V1 = 0.25 [(D2/D1)^2-1] + 1 (e.g. 243Win/260Rem/7mm08/308Win)
V = velocity
D = bore diameter

3. Change in case capacity, same bore size: V2/V1 = 0.25 (C2/C1 - 1) + 1
V = velocity
C = case capacity net of bullet volume

From 1, your 162 grain bullet would be going 93% of the speed of a 140 grain bullet
(e.g. 140grain = 3000fps ==> 162grain = 2796fps)

Very helpful formulae there