Joe,

  I guess you could say I'm fully aware of what the nuclear regulatory agency wants as I spent quite a few years as a nuclear welder and having to qualify yearly under Section 8 & 9 of the ASME Boiler and Pressure Vessel Code, using positions 1G thru 7G.

  But you're right on about flight calculations being a part of Pressure (PA) & Density(DA) Altitude. A pilot who shoots quite a bit of LR is where I got the idea. He uses this method for sight setting changes. I'm not sure whether this method will work at Schuetzen distances since changes will be quite small compared to 1000 yds., and might be lost in wind and mirage and other factors. 

  But I want to take it a step further. As you know bench shooters will often change their powder charges between relays because they felt their groups weren't going like they should. In all the years I've read about these shooters I've never heard mention of "how" they knew which way to go. Is this by chance, long experience, or have they some "formula" that tells them which way to go?

  I'm figuring that since changes in group size are due to changes other than MV/SD/ES if you haven't changed anything in your load, then, if a load starts to go "bad" during a match it must be due to some exterior influence.

  As we know humid air is less dense than dry air, so as the humidity level changes from the early morning hours to late afternoon, might not this difference make a difference in the bullets flight? If this is so then we would have to change our load slightly to get back on track.

  To take an example..... Where I live is 970 ft. Above Sea Level. Doing the calculations I've seen PA go as low as 805 ft. to 1008 ft. in the course of half a day. Doing the calculations for DA I've seen that run from 1000 ft. to 3010 ft. within the same time frame. Of course since temp. (C.) is a part of figuring DA that has to be taken into consideration.

  So, a lot going on when we shoot and it all has a negative effect on our shooting unless we can learn to deal with it.

  As for SD being a respected way of testing things..... I'll certainly agree with that. I'm just not sure that considering the variables we shoot under, that it can be used to generate 95% certainty for a load. As Joe pointed out, if the average group size for two loads is within 1%, not an unreasonable expectation when determining differences in two loads, you would have to fire over 4000 five shot groups in order to reach the excepted 95% accuracy level to be sure you have the right load. Even for a difference of 10%, firing 38 groups is bordering on undoable.

  So far no one who supports Statistical Analysis (SA) has said what is a reasonable number of groups to fire. That's all I ask! If a number can be brought forth that is reasonable, then I can use SA as a method to predict load confidence. Otherwise I don't believe it's totally applicable to shooting unless you want to spend that kind of time and money to prove things out, and I will continue to do it the "old fashioned" way.

PETE

Joe,

  Sorry to read you think I'm prejudiced against SD and SA, and have your mind set that anything I have to say is not valid. Einstein was right!    Guess we better drop the whole idea.

  I guess if you don't know what PA and DA is then you have some more to learn. That's the part I like about shooting. There are so many things I don't know, and so many avenues to explore. Short of giving a lesson on how to calculate both these conditions, what I wrote in my last message gives a general idea of what they are and a little on how they are, and possibly could be, used in shooting.

  Besides it should be put into another thread if there was any interest!

PETE

Forrest,

 Glad you chimed in on this, as I'm sure I might not have gotten things exactly right in this PA, DA thing. "Cuss and discuss" is right!   Lots of cussing on my part before I got it thru my thick head what had to be done. PA almost had me giving up!

 Just sitting here reading your message and note that you said you've never shot below a DA of 2000 ft. For the record Forrest lives at 4000 ft. It got me wondering, so I figured out my PA & DA right now. PA is 324 ft. and DA 1328 ft.

 But then a thought hit me. That's using an inside temp. of 72 deg.'s F. and the outside temp is 35 deg.'s. So figured that out and it comes to a PA of 314 ft., and a DA of 1140. When you know that my actual altitude is 970 ft. you can see how the changes are, and how they can affect POI, and possibly group size because of the different air resistance.

 For those not up to speed on this you can see the changes in DA and that's what Forrest uses, as it changes, for changing his sight settings.

 You might wonder why we have PA in there. The calculation for DA is determined by the PA and the current temp. in deg.'s C. PA is figured by adding or subtracting a set amount from the actual barometric pressure using the "Standard" of 29.92 inches of mercury as your base. This figure is then used on the "computer" to figure the DA.

 Sounds kind of complicated, and I'm probably not explaining it exactly right, but it's pretty easy once you get the hang of it. OR..... You can buy a Kestrel 4000 and it does the figuring of both for you!  

PETE

Keith,

  That's why I suggested buying the Kestrel 4000. It's advertised in Precision Shooting. It'll do everything you mentioned and a whole lot more. But, you'll have to calibrate it for a known barometer setting and the altitude of your current location, in the right order. Not for the faint of heart either as the instructions aren't any to clear in that area.

  Another very big BUT. The Kestel costs about $325 and a flight computer costs $12. If you can afford the former, go for it. If not, a person can do a lot of calculating for $300.

  It sounds complicated because I'm not a very good teacher. But once you grasp the idea it just takes a minute or so to come up with DA. Less when you get the hang of it, as when I do it things seem to be backwards of what they should be so it takes a little time to be sure I've got it right.

  Grasping PA was what got to me and only because I was assuming things that weren't true so my calculation for that was skewed. One of the problems of trying to get an idea across over a period of several days emailing. As you can see by what we've got here now, and we haven't even got into doing any "work"! 

  Once you have PA then you just plug that and deg. C. into the computer and DA is the result. The only other known you need is the altitude of the range you're shooting at. Those can be gotten frorn USGS topo maps that are free for the downloading off the web.

PETE

Forrest,

  Looks like there is some interest considering the number of views. But like most other threads on here, everybody wants to "suck" the info up without contributing to it by offering info or asking questions. Seems to be a real lack of curiosity on here.

  That's why I've been purposely vague on how to do the figuring, and what you do it with. Us two know what we're talking about yet we're the only ones participating. Not much sense going over what we've hashed out in private email if there's not enuf interest for people to ask.

PETE

Pete has been explaining it to me, and it is another thing that can possibly help with our shooting. After he explained it to me, I remember one Sat. last summer we were shooting in our league, took a lunch break. When I shot my next relay I though someone had messed with my scope, as it was shooting higher than before lunch. I know that Brent didn't mess with the scope as he was with Pete and I. This DA really sounds like it can help if one wants to get with the program and keep a record of conditions. We're not all just sitting back. If Pete doesn't share his Kestrel, probably have to dig up the jar in the back yard and gete some money out to buy one( always need another toy)
Bob

Bob,

Bob: If Pete doesn't share his Kestrel, probably have to dig up the jar in the back yard and gete some money out to buy one( always need another toy)

F:  Pete doesn't have a Kestrel I don't believe. He went out and bought a E6B at his local airport. Cost: $12

This is a simple mechanical computer, no batteries, two moving parts and some numbers around the dial.

This, a thermometer, one calculation and a spin of the wheel and you've the DA displayed under the little arrow. 

It will save you from the high/low miss if the temperature changes over the course of your lunch period or any other delay.

Good morning,
Forrest