Surprisingly good consistency across Lake City (5.56) headstamps?


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dboyles
May 16, 2010, 04:52 PM
I ordered a bunch of once-fired Lake City mixed headstamp brass from Brassman a few months ago, and I did some initial testing of case capacity across different headstamps to compare them to the brass I was previously using (Prvi). The Lake City had a higher capacity, so I went ahead and used the loadings that I used with Prvi brass as a starting point.

Today I did a little more in-depth testing to decide if I needed to sort based on different LC years to get the most accuracy out of the brass. I carefully crammed as much H335 as I could into a ready-to-load case, leveled it off at the case mouth, and poured onto the scale tray. I did five LC07, five LC08, and one LC91 oddball that I found.

The sample sizes were small, but the extreme spreads and the standard deviations looked really good, even across different head stamps. I also measured the cartridge length, and it looks like the deviation in case capacity can be largely explained by small differences in case length.

headstamp: weight; length
LC91 (one pc): 31.0gr; 1.7505"
LC07 (five pc): avg=31.14gr stdev=0.0894gr; avg=1.7518" stdev=0.0010"
LC08 (five pc): avg=31.20gr stdev=0.1225gr; avg=1.7525" stdev=0.0023"

I ask about this because when I went looking for other results, I found this tidbit (http://accurateshooter.wordpress.com/2008/01/19/federal-lake-city-223-brass-on-sale/) where they mention a 0.61gr stdev for Lake City, which is held up as being more consistent than Remington.

Is my test flawed by using powder rather than distilled water?

edit: I just remembered that these cases had also been pre-sorted by weight, so the cases used were within ~0.3gr of each other. That could certainly explain the favorable results. It looks like I can probably just sort by weight and know that capacity will generally fall in line.

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