Comparison Loading

[danr55]

In reviewing some of my loading data, I've found that load density seems to be strongly related to the accuracy/velocity mix. Most of the loads that I build, across the board, using different bullet weights, will contain the same weight/volume of powder, but different powders. That is to say a rifle that shoots a 180 grain bullet with 72.5 grains of IMR 7828, shoots a 165 grain bullet with, say, 72.3 grains of IMR 4831. I found it curious that the powder weight/volume ratio remainded so close. The greatest change being in the buring rate. Anyone else see this type of comparison?

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Dan AZ www.huntandlodge.com

 

[Calif. Hunter]

I have noticed that the fuller case volume loads do work better that the "half full" loads, but not to the level that you have as far as actual charges with different powders...knowing you,though, I will start watching it! A very interesting point...

 

[concerned hunter]

That is what I was wondering because I wanted to load some lighter bullets to hit the same place my 150's do so I don't have to mess with my scope settings.

 

[danr55]

CH, I did not mean to imply that the bullets would strike the same point of impact, only that the best performance would be gained with an equivilant volume of powder. The point of impact is a different story. It may of may not be the same.

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Dan AZ www.huntandlodge.com

 

[concerned hunter]

Is it possible to load two different grains of bullets and have them reasonably acceptable as far as hitting the bullseye? Like maybe a 140 and a 160 gr. bullet?

 

[Nodak Hunter]

That all depends upon the individual rifle. I have a .338 that has virtually the same point of impact at 100 yards for my 200 grain load, my 225 grain load, and my 250 grain load.

On the other extreme, I have a .308 that shifts the point of impact by 3" when I switch from 165 grain to 180 grain bullets.

The barrel vibrates and bends as the primer explodes, pressure builds, and the bullet travels down the barrel. If your muzzle is in the same spot for bullet X as it is for bullet Y when they both leave the muzzle, then they will have nearly the same point of impact at close range. If your muzzle is at it's maximum angle down for bullet X, and maximum point up for bullet Y as they exit, then bullet X will hit significantly lower than bullet Y at close range.

The only way to find out is to shoot a lot, and tinker around a lot.

 

[danr55]

The man hit the nail on the head. Not only is it moving, it's moving in an eliptical motion. If you can time the exit at the same point with each bullet, theoretically, depending on the gyroscopic forces of the bullet, each bullet should land in the same place at the same distance. That is very symplistic, but that is basically how it works. One of the best way to insure that the distance between the exit locations is minimized, is to dampen the oscillation of the barrel. One of the best ways to dampen that oscillation is to shorten the moment of the barrel. That's why I am such an advocate of pressure pointing barrels.

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Dan AZ www.huntandlodge.com

 

[deadeye2]

I have two rifles that will shoot three different bullets within 3/4" @ 100 yds. I feel this is rare, as all the others will not. The fuller the case,the better??
What about a real light load of real fast powder in a big case, say a 300 WIN. MAG.? Can this be a problem???
Be safe, have fun!
deadeye

 

[danr55]

Deadeye, I can't explain why, when the volume of powder gets below a certain proportion to the volume of the case, some very interesting things happen to the internal pressures. You would think that pressures would go down, but they go up. Dramatically. With fast burning powders, you increase the pressure rise to a point where the bullet won't move down the barrel fast enough to keep the spike under control. It's not the the pressue is greater than with slower powders, it's just that it gets there faster. What most folks don't consider is that the reason a bullet moves is because the pressure in the chamber needs to be reduced. It's kind of like opening a stuck door. You can push on it all day and it won't move. Smack it one time with your fist and it opens right up. Not any more pressure, it just gets there quicker.

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Dan AZ www.huntandlodge.com