Altitude affects on powder burn efficiency

[rumshooter]

I would like to start by thanking those who went to the trouble of helping me find a starting point with the E-Tips. It seems as though all of my loads are low as compared to the load data. I live at 8800 ft. in elevation and was wondering if there is any correlation between altitude and the low velocity that I see on the graph.

 

[Bruce Mc]

The difference in velocity caused by altitude is a factor of atmospheric conditions as it relates to the flight of the bullet, not the effect on the powder burn. Altitude and the barometric pressure variance because of it are not of any significance in the chamber of the firearm. Low velocities compared to the listed data is nothing new. We have all experienced this. That variance is due to so many variables that it would take a while to list them. Two biggies are varying chamber dimensions and different powder lots.

 

[Ridge_Runner]

most probably just a slow barrel, unless the barrel does in fact shoot faster with said loads at lower elevations.

Is it factory or custom barrel? my kreiger barrel is much slower than my lilja's due to it being cut rifled.

I sight in and do my load developement at 800 ft, and hunt/shoot at 3000 and the velocities stay pretty close just changing elevations. temperature will change velocity more than any other factor.
RR

 

[Guest]

I think I replied to your first post about the E-Tips, so this may be redundant. Your loads are fine, so far. You did the smart thing and started low. If you're seeing pressure signs, you should stop. If you're not seeing signs, you could creep the charge up carefully. If you are seeing signs, move to a slower powder, as I've had good luck with slower powders under E-Tips so far. Work up slow and carefully from the start charge, and I bet you'll find what you're looking for.

Remember, too, that the E-Tip is going to have a much higher BC than comparable weight bullets of traditional lead core design, so your trajectory will still be good at slightly lower velocities.

These E-Tips are a little finnicky, in my experience, but they are worth the trouble, as well, as I have had excellent results with them when I found the right combination. They didn't shoot middle of the road for me - it was either 3+ inches or under 1 inch.

 

[bullet]

I think I replied to your first post about the E-Tips, so this may be redundant. Your loads are fine, so far. You did the smart thing and started low. If you're seeing pressure signs, you should stop. If you're not seeing signs, you could creep the charge up carefully. If you are seeing signs, move to a slower powder, as I've had good luck with slower powders under E-Tips so far. Work up slow and carefully from the start charge, and I bet you'll find what you're looking for.

Remember, too, that the E-Tip is going to have a much higher BC than comparable weight bullets of traditional lead core design, so your trajectory will still be good at slightly lower velocities.

These E-Tips are a little finnicky, in my experience, but they are worth the trouble, as well, as I have had excellent results with them when I found the right combination. They didn't shoot middle of the road for me - it was either 3+ inches or under 1 inch.

It is important to note that higher velocities do not always mean higher pressures as lower velocities do not always mean lower pressures. That is why a chronograph is not a sole means to determine pressures as is looking at brass and primers a sole means of determining pressures. Unless you use a gage system on your rifle to determine pressures you can not really be sure what you are getting. Case in point was when I was getting 3060fps out of a 30-06 using a 165gr HPBT made by Sierra and I assumed it should be giving me high pressures but my primers were not flattened, neither was the base of the case expanded very much at all. So we used a gage and attached it to my Mark V and fired three rounds and even though the velocities were high with the load we were only at 53,665 on pressure. The modern 06 can take much more just like the 270 or 25-06. Unless a person actually uses a pressure gage set up on a rifle you really don't know where you are. It is good to know that my 3060fps load was not an extreme pressure load. I now have back down to 2953fps and not because of pressures but because I was able to tighten the group up some more and ended up with an exaggerated hole for a three shot group.

 

[Guest]

Bullet is on the money regarding pressure signs and chronographs. I don't own a pressure trace system (the little 'gauge' setup bullet is talking about), but I also find them to be just one more subjective measure. If you don't have a laboratory derived baseline pressure reading, it is impossible to calibrate the gauge to your rifle, and the pressure readings are simply relative pressure readings. Now, does this mean a pressure trace system (or some other similar strain-gauge setup) is worthless? Not at all. They must be combined with other known measurements, and compared to reference loads (factory loads are good for this, as they are generally uniformly below max) to provide a picture of the true internal ballistics of things.

I do consider a chronograph to be an invaluable tool for handload development, and in fact rank it up there with the press in terms of importance to handloading. I use mine as a guide to what is happening with my rifles, and I can generally figure out a rifle after a few load workups with different powders and bullets, and then have a reasonable frame of reference for future loading projects. In fact, the E-Tips in my 270Wby is a prime example of this. I found numerous combinations that were very fast (3400-3500fps for 130gr bullets), and all of them behaved similarly in terms of pressure signs with regard to the brass, primers, and bolt lift, among other things. I was able to work up the E-Tips after some preliminary testing showed them to generate a bit higher pressure for a given powder charge versus lead core bullets, with the same pressure characteristics. Please note that I did not work anything up above published max to achieve these velocities, and while working up, I did not get any cratered primers or case-head malformations, or sticky bolt lift. So when I worked up the E-Tips, I knew what to expect, when to expect it, and was prepared with lower overall charges across the board. I got what I wanted, as well - velocity and accuracy combined in a flat shooting 130gr load.

 

[bullet]

Bullet is on the money regarding pressure signs and chronographs. I don't own a pressure trace system (the little 'gauge' setup bullet is talking about), but I also find them to be just one more subjective measure. If you don't have a laboratory derived baseline pressure reading, it is impossible to calibrate the gauge to your rifle, and the pressure readings are simply relative pressure readings. Now, does this mean a pressure trace system (or some other similar strain-gauge setup) is worthless? Not at all. They must be combined with other known measurements, and compared to reference loads (factory loads are good for this, as they are generally uniformly below max) to provide a picture of the true internal ballistics of things.

I do consider a chronograph to be an invaluable tool for handload development, and in fact rank it up there with the press in terms of importance to handloading. I use mine as a guide to what is happening with my rifles, and I can generally figure out a rifle after a few load workups with different powders and bullets, and then have a reasonable frame of reference for future loading projects. In fact, the E-Tips in my 270Wby is a prime example of this. I found numerous combinations that were very fast (3400-3500fps for 130gr bullets), and all of them behaved similarly in terms of pressure signs with regard to the brass, primers, and bolt lift, among other things. I was able to work up the E-Tips after some preliminary testing showed them to generate a bit higher pressure for a given powder charge versus lead core bullets, with the same pressure characteristics. Please note that I did not work anything up above published max to achieve these velocities, and while working up, I did not get any cratered primers or case-head malformations, or sticky bolt lift. So when I worked up the E-Tips, I knew what to expect, when to expect it, and was prepared with lower overall charges across the board. I got what I wanted, as well - velocity and accuracy combined in a flat shooting 130gr load.

Seems like you did your home work and are more of a hand loader than you have let on in the past. Good stuff and the work has produced results along with satisfaction. Thanks for taking the time to explain your process with the E-Tip. I found myself having very similar results as you did. Either big groups are groups just under an inch. It is a picky bullet but when you get it right because of it's BC it will be hard to beat.

 

[Guest]

Seems like you did your home work and are more of a hand loader than you have let on in the past. Good stuff and the work has produced results along with satisfaction.

Well, I recently stayed at a Holiday Inn Express...