September 30th, 2010

.243 Win Brass Comparison Test — Surprising Results

A while back, Forum member Andy (aka GrayMist) did an interesting test, with five (5) different types of .243 Winchester Brass. He collected Federal, Lapua, Remington, and two different lots of Winchester-brand brass. Then he selected ten (10) cases at random from each brand and measured their weights. To ascertain case capacity, three (3) cases from each brand/lot that were closest to the average weight for that brand/lot were selected. The results were surprising: there was less than one (1) grain capacity difference between all the cases, even with a 14.7 grain maximum difference in case weight!

Measuring Procedures
The cases were sized in a Redding body die then primed with a spent primer. All were weighed before and after filling them with distilled water. The capacity shown is an average of all three (3) cases from that lot and represents grains of water. Note, I tested two lots of Winchester brass. Lot A was purchased in 1999. Lot B was from factory .243 ammo. There is a rather large disparity in case weight between the two lots.

Brand Federal Lapua Remington Winchester A Winchester B
Capacity 53.9 54.4 53.7 54.8 54.8
Aver. Weight 173.28 173.13 165.34 158.58 166.44
SD¹ 0.46 0.39 0.17 0.58 0.42
Range² 1.70 1.10 0.40 1.80 1.40
% of Avg.³ 0.98% 0.64% 0.24% 1.14% 0.84%

1) Standard Deviation in grains.
2) Range is the difference in weight between the heaviest and lightest cases in the test.
3) Case range weight divided by the average weight.

.243 WinchesterWhat the Numbers Mean
… And Some Speculations

Andy observes: “It certainly seems there is a huge difference in case weight between Winchester lot A and any other brand of 243 tested. What is also surprising is that there was less than one (1) grain capacity difference between all the cases, even with a 14.7 grain difference in case weight!

Should one be wary of trying the same loads that were initially tested in the light weight Winchester brass even though the capacity difference is small? I have had some interesting results with one brand brass that I cannot pass on yet, except to say I sent that company a sample of the lot I have been using. The Remington brass weight range was very low. These were taken from a box of once-fired factory ammo. I will have to acquire some more and measure it.”

Results of Larger Lapua Sample
In a previous session Andy weighed all 100 Lapua cases he had on hand. His measurements showed a total variation of 2.1 grains, with the weight range being 172.5 to 174.6 grains. That is a 1.2 percent spread. The most that came in at the same weight were 11 cases at 173.5 grains.

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