I think that “equal skirt length” of gas check is very important for great accuracy. Equal skirt length also equals even thickness of skirt for better bullet concentricity after sizing. So recently I started using my dial calipers to check for equal length. For example one .223 gas check skirt can vary as muck as .001-.004 in length (one side longer than other). One box of my Hornaday checks only had about 500 that were near perfect.
The shape of base can sometimes vary also. Most were more flat and uniform, but a small few were more rounded and thrown out.
I once sanded skirts evenly, but this does not cure the wide thickness variation of skirt. Also seems that the checks with sanded skirts fell off easier in flight?
Little details like this along with a more perfect snug fitting cast bullet can improve accuracy .
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