logarithmic Load Estimator

[Black Beard]

In Mr Lee's reloading manual he suggests that velocity and maximum pressure follow logarithmic curves against powder charge. He provides a method of estimating the velocity and pressure for a given load.

Is there any interest in a excel spreadsheet that does the same thing based on 2 known points (eg the starting and maximum loads)?

The spreadsheet is designed to estimate the load, velocity or pressure between the starting and maximum load and so give you an indication of what is going on.

It seems to work pretty well based upon some limited velocity testing in 7.5mm/310 cadet. Also looked good when checking the book loads for cartridges which have multiple loads for the same bullet and powder (eg 45/70).

It doesn't seem to work well with high load densities of trail boss (velocity seems to flatten off- don't know why).

BB

[303Guy]

Is there any interest in a excel spreadsheet that does the same thing based on 2 known points (eg the starting and maximum loads)?Hell yes!

Many moons ago I plotted powder charge against velocity (this was pre Excel) for several loads and found the curves to quite interesting. It seemed to explain the seemingly odd max loads listed with lower pressures for some powders than others. The pressure was spiking rapidly. That's going by pressure signs on the case and the shape of the velocity curve.

Another interesting presentation of loads is plotting load against muzzle energy and also load against muzzle momentum.

One thing I found is that a powder that maintained a steady rise with load increase was more accurate than one the tended to climb rapidly toward the top end.

[frnkeore]

I assume that your talking about the Lee, Grain/Factor and Velocity/ Pressure ratio?
If so, second YES, from me. I like what he has done with it but, a Excel program would be a lot better.

Frank

[Black Beard]

Okay, PM me an email address and I'll send you a copy. Please let m know what you think. BB

[Larry Gibson]

The old slide rule Powley Computer did the same. However, many powders, especially ball powders, exhibit "logarithmic curves" only in a narrow band of pressure. They can be especially bothersome not following a "logarithmic curve" at lower and higher pressures. Additionally some powders such as Hodgdon's LeveRevolution burn much differently based on the case capacity, bullet weight and expansion ratio and do not follow "logarithmic curves".

Larry Gibson

[oldblinddog]

Does anyone make a Powley computer? And, if not, why not?

[Black Beard]

Thanks for that Larry. Of course something like this needs a certain amount of common sense. For example, a 70 % charge of H110 isn't going to be clever, no matter what a simple calculation says. The further you go from real data, the less reliable it gets, which is why I think the approach only works between published starting and maximum loads.

[Larry Gibson]

"The further you go from real data, the less reliable it gets,"

How true that is Black Beard!

I started using the Powley Computer (I still have it btw) back in the late '60s and I thought it was pretty slick and was telling me everything I needed to know. Then in the early '70s I got my first Oehler chronograph........That's when I found that the while the Powley computer most often gave a good guestimate of the velocity there was enough variation outside of statistical boundaries to call it's ability to guestimate into question. The Oehler M10 with Skyscreens was the 1st easily used chronograph and gave many of us back then 1st hand knowledge of actual velocities. The generally accepted published data was also being called into question with the result being much more reliable published data these days.


I guess my point is that numerous methods have been devised to questimate velocity and psi including QuickLoad of today. I've no problem using them as I still use them also for initial load development. However, since using my two Oehler chronographs (M10 and M35P) for years and the Oehler M43 to measure velocity and psi for the last 8+ years I've come to see enough discrepancies between the calculated velocity and psi with real world measured velocities and psi's that I still always refer to published data where available and work up judiciously. When using components where data is not available I am very, very judicious and always work up the load.

I have stopped testing mid stream numerous times with some components in some cartridges because I can see bad things beginning to happen in the pressure figures and pressure trace the M43 gives. My advise to those who want to use such and such a powder because they have it is simply; if you are not very, very experienced at load development and can find no published data for a certain powder in a certain cartridge then understand there is probably a good reason why. Find a use for the powder in a cartridge where there is published data or trade the powder for one more useful in the cartridge you have. In most instances it will be much safer for you and the firearm that way.

Larry Gibson

[Black Beard]

Spreadsheet sent off to Frank.

Hope it is useful.

[Tar Heel]

The old slide rule Powley Computer did the same. However, many powders, especially ball powders, exhibit "logarithmic curves" only in a narrow band of pressure. They can be especially bothersome not following a "logarithmic curve" at lower and higher pressures. Additionally some powders such as Hodgdon's LeveRevolution burn much differently based on the case capacity, bullet weight and expansion ratio and do not follow "logarithmic curves".

Larry Gibson

^^^^^^^^ As Larry points out, there are NO ABSOLUTES with pressure curves ^^^^^^^^

[Whiterabbit]

One thing I found is that a powder that maintained a steady rise with load increase was more accurate than one the tended to climb rapidly toward the top end.

Of course. a slower rise @ same charge increase rate means that variance from load to load will change your velocity less. In short, large velocity swings with small powder charges mean higher sensitivity to loading practices (and ultimately downrange results).