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Posted: 12/3/2007 7:37:08 PM EDT
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What is the distance between the edges of the feed lips on a 6.8 SPC magazine? A .223 mag is ~.445". Thanks |
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5.56 brass is .375" wide at its rim. 6.8 brass is .418" wide - an increase of 11.5%. 5.56 feed lips are .445-.450" wide; adding 11.5% gives .496"-.501". Mmmm, so they did not proportionally open 6.8 feed lips, or they did and it proved unreliable and reduced the opening spec. Interesting. |
You forgot the Radius Rule: In dealing with the mechanics of a circle... The Radius Rules. And the radius is half of the diameter. Therefore, 0.445" x 11.5%/2= 0.4705" The zero in the thousanths is considered an even number and therefore, does not get rounded up to make the final answer 0.4710. There is a reason why I buy all my 6.8 mags from PRI. They know math. |
I never knew this Radius Rule - thanks for the info. |
I, too buy them because they work, and work, and work. I am on probably round # 2000 or so out of my second 6.8 SPC, and I have never had a single FTF or FTE malf., except for when I was shooting the SSA Extremems out of a Model 1, and that really doesn't count, LOL   . I am quite sure the M4 feedramps have made a significant difference, too.Of course, YMMV |
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