I've been trying some new 9.3 x 74 loads and perusing my manuals and the internet to find some that work at lower pressures, esp for use in my old drilling. I noticed that Accurate 3100 supposedly generates much lower pressures with higher velocities than 5744 with the same bullet. I enough engineering courses to be extremely dangerous when drinking beer. Kind of like a college freshman after his first psychology class. So, seems to me if you lift a 270 grain pill faster, it should have more pressure under it. Some old chemistry stuff related to Boyles and Charles laws and Newton and his equal and opposites. Can somebody get in behind my steel plated skull and explain this to me.
Thanks
Bfly

I will try. The smaller amount of 5744 will hit max. pressure quickly be totally burned and follow the natural gas expansion cuve and exhaust at a relatively low pressure.

The 3100 will approach high pressure slowly continue to burn at lower than max pressure releasing a lot of energy. After it finishes burning and the bullet is farther down the barrel and the natural expansion curve of the gas will be followed and will exhaust at a higher pressure than that of the 5744.

The area under each PV curve will determine each energy release and that of a full load of 3100 can well be much greater.

Lets try it this way. A small amount of fast burning powder can be limited by reaching max. pressure before it can contribute any significant energy ( just not enough powder).

A much larger amount of 3100 never reaches max, pressure, burns completely and has a much larger energy contibution. roger

Simple explanation:

F=MA Force accelerates mass. The more force is applied to a given mass, the more it is accelerated

P=F/Area Pressure equals Force per unit area. If area is constant, the greater the is the force.

This causes you to question how a round showing a lower pressure can cause a higher velocity.


BUT ...

Velocity is the result of acceleration over time.

If a smaller acceleration occurs over a longer period of time, the resulting velocity can be greater.

How can this happen? It could occur if the powder burns SLOWER. Remember that the pressure value we look at is peak pressure. The real phenomenon is a curve ... The powder is ignited and the pressure climbs and the bullet moves forward. If the powder burns quickly, the pressure will spike and begin to fall as the powder is consumed and the volume in the bore behind the bullet is increasing.

With a slower burning powder, the pressure curve may be lower in absolute height but will be longer in duration because powder is still burning and generating gas as the bullet moves further down the bore.

If we look up AA3100's burn rate ... we find it is much slower than AA5744. So we can expect the burn curve to be broader for AA3100 than for AA5744.

So the bullet is accelerated for a longer period of time and that yields a higher velocity.

Thanks guys, I knew it couldn't be that complicated. I suspected it was pressure curves, but on my own, just couldn't figure it out.
Bfly

Yeah, It's the curve. Energy imparted to the bullet is the AREA under the curve, not the peak pressure. It is almost intuitive that a powder with a short, spikey pressure curve will impart less total energy to the bullet than a powder with a longer, albeit flatter, curve.

Fast Ed

Oh yeah! Areas under the curve.....the first deriviative of the .... ....vague memories from hot afternoons in Calc class in the late sixties.
Bfly

My vague memory of calc (in the early 60's) is its the integral of the curve to get the area under it...the deriviative gets you the slope of the curve.

Pat

I stand corrected. Thanks, I told you they were vague memories. And I really didn't understand it back then. Prof spoke English as a third language. I wasn't interested. Girls were wearing minie skirts.
Calc seemed like magic until Handloader put out that series called Pressure Factors. Then I read some of Homer Powley's stuff and it started to make sense.
Bfly

Pressure decreases because of the increasing volume behind the moving bullet.

There were at the end of WW3 some interestimng approachs to overcome this limitations for long distance and high speed artillery and tank guns. One was too use a conical not cylindrical barrel diameter (large dia. at the rear, narrow at the muzzle), another one was to use additional propellant charges along the barrel.

Then came rocket technology...

These modern powders are quite high tech. Progressive burn rates - fast burning components get the bullet moving before the slower components burn. My hornet just about doubles its power with Lil'Gun over standard powders (well, its seems like it). It's quite amazing. But put that powder in a larger case and it goes the other way - excessive pressure! There is also the issue of powder density. More powder with slower burn rate means more velocity at lower pressure.

I don't know whether Accurate 3100 behaves in a similar way but a curious thing with Lil'Gun is that changing neck tension has a profound effect on velocity (from zero to very firm). At certain powder charge levels, there is a significant change in pressure and velocity but at the top end - where the powder is heavily compressed - the pressure difference is not that noticeable but the velocity is very different.

[QUOTE]Originally posted by DUK:
.

There were at the end of WW3 QUOTE]

I missed that one or just plane forgot it. roger