Reloading Data?

Magload · #1 07-19-2016, 02:57 PM

I can not find this listed in my manuals. When they publish velocity for a given load is that high, Low, or average velocity? I have been using average velocity from my Labradar for my spread sheet data but it really looks like I should be using high if I want to compare it to the manuals. What say anyone?

If you were to ask me what velocity I got today from my new 148gr plated DEWC from X treme what figure would you want?

fredj338 · #2 07-19-2016, 03:13 PM

Quote:

Originally Posted by Magload

I can not find this listed in my manuals. When they publish velocity for a given load is that high, Low, or average velocity? I have been using average velocity from my Labradar for my spread sheet data but it really looks like I should be using high if I want to compare it to the manuals. What say anyone?

If you were to ask me what velocity I got today from my new 148gr plated DEWC from X treme what figure would you want?

Generally it's average velocity for a series of shots; 5, 10, 20.

rockquarry · #3 07-19-2016, 06:10 PM

It's an average, but this average may vary from day to day depending on conditions; seldom of any great significance.

Magload · #4 07-19-2016, 07:16 PM

It would seam to me the high would be the most important as there is where the max pressure would be. If you had a big extreme spread the pressure difference between average and high might be important. I would bet when we buy ammo the velocity the manufacture list is the High.

BB57 · #5 07-19-2016, 07:58 PM

It's an average velocity.

It's actually the average velocity that matters and bullet velocity follows a normal distribution pattern with 68% of the shots falling within +/- 1 standard deviation of the average velocity, 95% falling within 2 SD of the average, and 99.7% falling within 3 SD of the mean.

What that means is that if you have an average velocity of 3200 fps and an SD of 20 fps, 68 out of 100 rounds will have a velocity between 3180 fps and 3220 fps, 95 out of 100 rounds will have a velocity between 3160 fps and 3240 fps, and for all practical purposes 100 out of 100 rounds will have a velocity of 3140 fps and 3260 fps.

In other words the extreme spread is about 6 times the standard deviation.

If you have the average velocity and the SD, you can more or less describe/predict the extreme spread as well as the maximum and minus velocities.

There's a lot more value in that than just listing the high velocity, as the high velocity by definition is in the right hand tail of the 3rd SD and represents only about 2 out of every 100 shots.

----

Why your velocity doesn't match the load velocity can be due to a lot of factors.

1. Revolvers, even with the same barrel length vary a lot in average velocity based on the particulars of the chamber, throat, cylinder gap and forcing cone. It's not uncommon to have a 50 fps difference in two identical revolvers of the same make and model.

2. Powder varies from lot to lot. As an example, it's been readily acknowledged that Win 296 and H110 are the same powder and have been the same for at least 15 years. Yet you'll see load data in the same manual that lists both H110 and Win 296 with significantly different max loads.

For example I have a manual in front of me now that lists data for 158 gr jacketed bullets with a maximum of 15.6 gr for H110 and 16.0 gr for Win 296. It also lists maximum charges for 180 gr bullets with a maximum of 13.7 grs for Win 296, with a velocity of 1100 fps and 13.1 grs and 1050 fps for H110.

This does a pretty fair job of illustrating the difference that occurs in different lots of the same powder.

3. Different bullets make a difference as well, and that goes double for plated bullets when compared to jacketed bullet data.

Plated bullets tend to produce pressures that are a little lower than jacketed bullets. Plated bullets have soft cores and comparatively thin jackets, so they take less force to obturate in the bore. As a result, a plated bullet will require a bit more powder to achieve the same velocity as a jacketed bullet of the same weight, shape, diameter and bearing surface.

Magload · #6 07-19-2016, 08:19 PM

Quote:

Originally Posted by BB57

It's an average velocity.

It's actually the average velocity that matters and bullet velocity follows a normal distribution pattern with 68% of the shots falling within +/- 1 standard deviation of the average velocity, 95% falling within 2 SD of the average, and 99.7% falling within 3 SD of the mean.

What that means is that if you have an average velocity of 3200 fps and an SD of 20 fps, 68 out of 100 rounds will have a velocity between 3180 fps and 3220 fps, 95 out of 100 rounds will have a velocity between 3160 fps and 3240 fps, and for all practical purposes 100 out of 100 rounds will have a velocity of 3140 fps and 3260 fps.

In other words the extreme spread is about 6 times the standard deviation.

If you have the average velocity and the SD, you can more or less describe/predict the extreme spread as well as the maximum and minus velocities.

There's a lot more value in that than just listing the high velocity, as the high velocity by definition is in the right hand tail of the 3rd SD and represents only about 2 out of every 100 shots.

----

Why your velocity doesn't match the load velocity can be due to a lot of factors.

1. Revolvers, even with the same barrel length vary a lot in average velocity based on the particulars of the chamber, throat, cylinder gap and forcing cone. It's not uncommon to have a 50 fps difference in two identical revolvers of the same make and model.

2. Powder varies from lot to lot. As an example, it's been readily acknowledged that Win 296 and H110 are the same powder and have been the same for at least 15 years. Yet you'll see load data in the same manual that lists both H110 and Win 296 with significantly different max loads.

For example I have a manual in front of me now that lists data for 158 gr jacketed bullets with a maximum of 15.6 gr for H110 and 16.0 gr for Win 296. It also lists maximum charges for 180 gr bullets with a maximum of 13.7 grs for Win 296, with a velocity of 1100 fps and 13.1 grs and 1050 fps for H110.

This does a pretty fair job of illustrating the difference that occurs in different lots of the same powder.

3. Different bullets make a difference as well, and that goes double for plated bullets when compared to jacketed bullet data.

Plated bullets tend to produce pressures that are a little lower than jacketed bullets. Plated bullets have soft cores and comparatively thin jackets, so they take less force to obturate in the bore. As a result, a plated bullet will require a bit more powder to achieve the same velocity as a jacketed bullet of the same weight, shape, diameter and bearing surface.

Thanks that is some great info. A little hard for me to completely wrap my mind around completely but I think I got the principal of it. The good part is I am not going to have to go into all my spreadsheets and Reloader's WorkShop and change my data.

Nemo288 · #7 07-20-2016, 05:07 PM

Also:
a) The book figures were more than likely NOT measured with the same length barrel
or at the same distance you did or with the same instrumentation which leads to:
b) HOW the velocity is measured makes a difference: My LabRadar is always slower than my Magnetospeed.
I am still working on a formula to justify these as I have several years worth of Magnetospeed data but just starting to use the LabRadar.
Entering all the shots I have taken with both into an array, the HP-50g gives a formula like: .9513*x^1.0074.
Yeah, not linear. I expect this to change as I get more data to analyze.
I am also still playing with the LR settings to see if things like the "distance" effects the results.

As long as all your data is measured the same way, you will soon get a handle on how your gun and loads work.
Just keep things as consistent as possible.

Magload · #8 07-20-2016, 07:43 PM

I am slowly reshooting all my loads past the LR. The amount of signal strength bars the display shows effects the accuracy I think. I have had to sit one leg of my pistol rest on the mounting plate with some guns. Part of my old data was done with my Magnetospeed but most was with my Prochrono.