I noticed something rather interesting today. I am working up a load for my 300 Win Mag with the Nosler 200 grain Accubond bullet and Ramshot Magnum powder. I tossed out all my used cases and started with new Federal Brass. I also have 10 cases of Lapua brass. The new Federal brass holds 84.5 grains of that powder to the base of the neck and once fired Federal brass holds 87.5 grains. Once fired Lapua brass holds 90.4 grains.

Anyway I fired 3 shots with new Federal brass and got 2890, 2857 and 2941 for an average of 2896. Then I fired 3 shots with the same powder charge in once fired Federal brass and got 2970, 2982 and 2977 for an average of 2976. So the extreme spread with new cases was 84 and the extreme spread with the once fired cases was only 13 fps. The difference in average velocity was 80 fps.

Now I know that only 3 shots each is not a good sample but the difference is big enough that it seems clear that new cases are not as consistent in velocity and they use up a fair bit of energy just expanding, rather than in pushing the bullet out of the barrel. Have others noticed this? If this is normal then it seems nearly impossible to use new cases to work up a load with or to shoot the desired load in.

I shot both groups at 250 yards. The new cases gave me a group size of 2.85� and the once fired cases gave me a group size of 2.67�. Not a significant difference in group size but the group centers were 4� apart which is significant.

While these are good groups, they are not at all what I had been getting back in August when I was using RL25. With 74 grains of RL25 I was getting 3030 fps and an average of 0.59 MOA for 6 groups (4 fired at 250 yards and 2 fired at 400 yards). Then I shot this load again this winter and group size was not nearly as good and velocity was only 2880 fps (150 less than in August). I assumed that the colder temperature was the cause of the much lower velocity so I decided to try Ramshot Magnum which is supposed to be much less sensitive to changes in temperature in relation to changes in velocity. But I am just not getting the kind of accuracy I was getting with RL25 at the higher velocity. I am concerned that if I work up the load again with RL25 at the colder temperatures to get the accuracy back (which will probably happen once I get back up over 3000 fps) then I will be too hot when the temperature is higher. Maybe I should try H1000. Perhaps it will give me the kind of accuracy I am looking for and was getting but will be stabile at various temperatures. Any thoughts or suggestions? Thanks, Rufous.

rufous, The velocity difference(slower with virgin brass) is normal as the brass is also forming when shot the first time. After reloading the fired brass you should see velocity being back up to normal with less spread. As far as the temp affecting the velocities, that is probably normal also. A hot load developed now in January in cold temps may be over the limit in July when it's 90 degrees! GHD

rufous, were your powder measusrements in the fired brass before or after resizing?
Difficult to attach any statistical significance to less than a 10 shot sample (minimum.) Shoot a lot more!
cukrus

Rufous: H1000 gives me the smallest groups of any powder in my .300 Win Mag. Not sure yet about whether it is more stable in varying temperatures, as Hodgdon advertises it is.

Just because the brass was all of one brand doesn't mean it was of the same lot, therefore one batch could vary significantly from the other. The operative question is what, if any, is the difference in capacity of the two lots AFTER firing (and before any type of resizing). This may shed some light on your velocity differences.

Also, as another poster mentions, your sample is far too small to draw any conclusions. Shoot some more.

As far as once-fired brass giving significantly different velocities as unfired brass of the same lot, phooey. Only if it is prepared differently, such as making neck tension grossly different, would there be any measurable difference.