Thursday, October 01, 2009

The Importance of Brass

I've been shooting Service Rifle for a little bit now, and I haven't paid too much attention to my ammo. I mostly shot inexpensive 55gr factory ammo that grouped around 3MOA.

Remington white box from the bench:

Georgia Arms from prone:

Earlier this year I got a 1:8 barrel, and some Sierra MK 69grs to go through it, but I haven't had a chance to try them out until recently. My first groups with the 69s were not any better than the 55s, about 2.5-3 MOA. After some reading, I decided to sort my brass by headstamp, load some rounds and head to the range. My first group with sorted brass:

Sierras in TW69 brass from the bench:

WTF? It turns out TW69 is really crappy brass made at the Twin Cities plant. During the time this brass was made, they were mostly concerned with productivity and not quality. Also, at least one of those shots on the right did not come from my rifle. Fortunately, I had also loaded some (mostly) once-fired R-P brass, and those fared much better.

Sierras in R-P brass from the bench:

You notice there are two distinct groups. One to the upper left with 6 shots, and one around the X with 4 shots (I think there's a double). When I got home, I weighted the R-P brass I hadn't loaded and found two distinct groups:

91| 1 1 3 3
91| 7
92| 8 9
93| 0 0
93| 9

key: 93| 0 = 93.0 grains
leaf unit: 0.1 grains
stem unit: 1.0 grains

What, you don't know how to read a Stem and Leaf Plot? Anyway, Some of that is once fired from the same lot, and some is range brass, but I can't tell which is which. My guess is that each kind groups pretty well, they just don't happen to group in the same place.

Now I've got my brass sorted into Lake City, Winchester, and 'Blaster.' I also weighted the Winchester and culled anything that wasn't within a grain of average. I'll let you know how they shoot when I get them loaded (daddy needs a case trimmer). Oh, and the Lapua brass should be here Saturday.

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