Sky C.,

  The E6-B Flight Computer is basically a stand alone item and no other equipment is needed. But you will need to know the barometric pressure, degrees Celsius (conversion chart on the E6-B) and the  "real" altitude of your location. You can get all this from your local airport, or Geological Survey Topo map that you can get off the USGS web site will give a more precise altitude. The idea is to have a base to work off of.

  A good source for the E6-B is at your local airport. It's where I got mine, and will also be a good source to show you how to use it. They bent over backwards to help me get the hang of it. They also have Sectional Aeronautical Charts covering your area that will give the altitudes, but I like the USGS maps because they are a little more precise. The E6-B comes in either plastic or metal. I have the metal one due to the airport sending in the wrong part number, (got a discount) but Forrest says the plastic one will probably last a lifetime, and is quite a bit cheaper. I wouldn't recommend getting any size smaller than the regular size, (didn't know there was more than one size) which is almost a pocket model anyway. The reason for this is even the regular size is none to large.

  The E6-B will come with an instruction book, but it can be a litle confusing since it's slanted for pilots, and unless you're familiar with the jargon you might have a little trouble digging out the pertinent info.

PETE

Pete & or Forrest-

I was digging back through one of the previous threads and located the following instruction:

[PETE] Figuring PA is easy. What you need is to know the altitude of your location and the barometric pressure.  Then adding or subtracting from your altitude will be determined by whether your barometric pressure is higher or lower than the "standard" of 29.92. Think of 29.92 as being like the constant used in the Greenhill formula.

My understanding is that barometric pressure changes at any location depending on various conditions...  Is there a "standard" barometric pressure correction factor for any altitude or are we talking actual barometric pressure at any given moment?

This is fascinating and I'd like to pay around with this some.

Thanks-

Sky C.

Sky C,

  Forrest pretty well covers it. A coupla things I could add would be to buy yourself a barometer, take it out to the airport and set it according to what they have on theirs. Then you wouldn't have to be calling all the time. I happen to have 3 of them around the house.

  Another thing is that Forrest is giving you advice for shooting at around 1000 yds. A point you might have gotten out of the associated threads on here is whether we need to be a little finer than 500 ft. differences in our acceptance of variations in DA at the shorter distances we use in Schuetzen shooting. Something we'll find out when the weather warms up.

  Forrest has proven that DA can be useful at the longer ranges. What I want to prove, or disprove, is if it's also applicable for 100 & 200 yd. shooting. I'm not worried about getting a hit on the target at 200 yds., but I have noticed that sometimes groups seem to wander, for no apparent reason. You then have to re-zero. I'm thinking that if you could look at the DA and know you have to move your sights, and with enuf previous data backing you up, you should be able to know almost exaclty how much you have to move them before you fire a shot. If this is true then it would save a lot of  time, Lead, & powder. Also some matches we shoot also say no sighters, and if you haven't shot for an hour or so, you could be off enuf to be out of the running.

  As I've mentioned in other threads on this topic, the whole idea might not work out, but if we don't try it we'll never know!

  Now if you really feel like spending money you can buy a pocket weather tracker like I did and you can get a direct DA reading off it, so you don't have to tire your brain out doing all the figuring...... plus it has a whole host of other things you always wanted to know but were afraid to ask.

PETE

Forrest - is the weather up your way permitting you to get out much these days?  We have been enjoying mild weather on and off with temps getting into the 60's already - only spots of snow here and there on the range.  I'm hoping to get out tomorrow for a shootin' session.


Sky,

Mainly it is indoors for us up here. I'm shooting in several 100 round Offhand Scheutzen matches this winter using the Stevens 44 1/2 with a 22RF barrel.

I do get out for some developmental shooting now and then when the WX warms up enough. Right now I have the fever for shooting my M1895 Marlin, which is barreled up in 40/65. I used this rifle in Q2003 to win "Lever Rifle" class and I want to do it again this year. I have recently built up a new combination with IMR 4198 and cerial filler that initially proved out well. Now I need to keep on checking it for consistency until June.

[Sky] By the way - nearest local airport to me is Vance-Brand - about 2 mi. from my house - about 5 from the range.

F: I'm not showing a airport by that name right here at home. If it is Longmont it isn't of much help since there is no instrument procedure there and thus no ASOS machine.

[Sky] Questions again:  

1)  If I'm understanding correctly then - the calculation involves correcting actual barometric pressure on the given day/hour//location to "standard" barometric pressure of 29.92" Hg.  Is this correct?

F: OK. Here it is: Say you call in or read your own barometer and the prevailing pressure at your location is 30.22 [pretty high]. You subtract 29.92 from 30.22 and come up with 0.3.

This means that your altitude above mean sealevel should be adjusted. Say you're at 5300 MSL, you then subtract 300 feet from your actual altitude to find Pressure Altitude which will be right at 5000 feet.

2) Is there a sufficiently accurate - and inexpensive barometer that can be taken to the range?  Recommendations?

F:  Pete has the idea here. Also keep in mind that barometric pressure changes, sure, but not very fast: Once per day should do it.

3) How accurate does the temperature used in the calculation need to be? 

F:  In my view the temperature and the way it changes is nearly everything. It has far, far more affect upon the density of the air than barometric pressure for a given location. Measure temperature as closely as possible and always in "C" so you may compute Pressure Altitude [as above] with current temperature to come up with Density Altitude.

[Sky] I'd like to try all this out on the cheap to start - the Kestral and similar gadgets are a bit pricey for now.  I can find a lot of other things to do with $300!

F: An E6-B will cost you about $12 or $14, and that will be a good metal one. One of these is all I've ever used. Portable, cheap, no batteries, lasts forever.

Good evening,
Forrest

Just to give you a feeling for DA, and it's difference between actual altitude and DA, my altitude is about 970 ft. or so, yet right now the DA here is 2122 ft.

PETE,

Is it really 70F back there?

Wow.

Out here it is a warm comfortable 20 and snowing.

Good morning,
Forrest

Forrest,

  Well, it's not 70 degrees outside, but it is inside!    Outside it's 35 deg.'s right now.

  But no fair reverse figuring on me. I was just trying to give an example on the differences between actual altitude and DA. Probably should have put in the temp.

Joe,

  Your example is the reason I want to try this DA thing out and see if different "thicknesses" of air will have an affect of POI at Schuetzen ranges.

  One thing I'm really interested in seeing is how rapidly things change as overnite moisture (dew) evaporates into the air and disipates. We know that the more moisture in the air the less dense it is, but does this mean, on average, that the DA will be higher? 

PETE