Load Manual Standard Deviation

[DesertRatR]

I use both Speer and Lyman load manuals. I have never been able to find standard deviation data reported for the speeds at the powder loads in the manuals. Other than SD data I develop on my own, is there any other source?

Also, I assume the average speeds are reported, and not the max, for the bullet and powder load listed. Is that correct?

[std7mag]

I have never seen Standard Deviation, or Extreme Spread listed in any manual.

Some of the gun mags have listed their chrono findings, but don't forget it is for their particular firearm and will probably be different from yours.

Manuals will usually list start charge in grains and velocity, and max charge and velocity.
It is up to you to find the accurate charge and velocity for your firearm in between what is listed in the manual.

[hounddawg]

definition of standard deviation
https://en.wikipedia.org/wiki/Standard_deviation

what load manuals list are the average velocity of their test guns

don't get too far into the weeds with the chrono numbers unless you are doing long range or benchrest. Just use the average velocity to make sure pistol loads will meet power standards or for basic ballistics tables for shooting beyond your scopes zero distance. The SD and ES are only useful for determining the consistency of your reloading methods and will not be relevant or useful for 99% of shooters/reloaders

[RC20]

Like pressures, I am interested in where I am at but most don't.

So I have I Lyman's to give me some idea though it does not have all the powders.

[hdwhit]

hounddawg wrote:
what load manuals list are the average velocity of their test guns

Do they use Average (i.e. Mean) or Median values? I have yet to see a published source of reloading data say one way or the other. Noticably absent from every reloading manual I have is a section entitled something like, "How we come up with our data". Sure, someone will tell you they used a particular gun or a universal receiver, but not HOW they did their test or compiled their data (probably because they regard it as proprietary information or trade secrets).

Further, some manuals, like Hornady, list a notional velocity for a given powder charge. That is, when Hornady lists a 14.2 grain charge of IMR-4198 under the 3500 fps heading for a 25 grain bullet in the 17 Mach IV cartridge, they are not saying it delivers exactly 3500 fps, nor are they saying that it averages 3500 fps; they are indicating the charge should get the bullet to a velocity in that range.

[T. O'Heir]

"...standard deviation data..." No such thing. All data in all manuals are averages. You can forget about velocities in manuals anyway. They only apply to the exact components and climate conditions on the day of the tests.
This kind of stuff is mentioned in manuals as well.
"...data I develop on my own..." That is a very decidedly unsafe thing to do.

[hounddawg]

Does it matter? If you are loading right they will be close. Within 50 FPS just guessing. This is not something I would lose sleep over

Here are 10 shots from my .260 last Friday 36.2 grains Varget 123 SMK, 26 inch barrel. Neither my older Sierra book nor the Hogdon site listed a load for the newer 123 gr bullet

Sierra V edition for 120 grain SMK and 36.1 gr of Varget at 2700 FPS
Hogdon Load data for 36.0 gr Varget and 120 bullet has it at 2716

2704,2715,2721,2715,2732,2715,2699,2721,2704,2715

Mean: 2714.1
Median: 2715
Mode: 2715
SD: 9.7

Shot over a Pro Chrono

[GeauxTide]

I've found the manuals (have Speer, Horn, Sierra, Nosler) to be very close to my loads. I use the chrony (Oehler 35P) to measure SD and ES. When both are low, the load is very accurate. When both are high, discard. Since my measurements are based on 10 shot strings, I don't know the value of a reading on someone else's chrony, brass, primer, powder, bullet, barrel combination.

[hounddawg]

They will be close if you are using close to the same barrel length as the test barrel, otherwise..

https://rifleshooter.com/2014/12/308...ty-28-to-16-5/