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Posted: 1/15/2009 6:01:35 PM EDT
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Hi all
I'm making match .223 ammo and wanted to know what is your favorite case length to start with. Thanks Will |
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Quoted: Sir, my answer to your question falls into the "YMMV" catagory. I trim all resized .223 Rem. brass to 1.758", and I do it each time I reload a case. That way I always know each case is the same length. 7zero1, out. I use a Dillon trimmer so my cases are automatically trimmed each time they need it so I too set my trim length at 1.757". The recommendation to set at 1.750" is made so that one doesn't have to trim each time. |
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The text and title of your request is not clear. If you are loading for one rifle with one set of chamber dimensions, then you should find the distance from the step in the chamber diameter that clears the casing neck, back to the bolt face or some other reference point. Subtract .010 from that distance and trim your cases to that number.
If you are loading for 5.56 x 45 mm NATO AR's in general (not just your personal match rifle) then you should trim to 1.750. The MilSpec for casing for M193 and M855 is 1.760 MAX. I interpret that to mean that the 3 sigma (99% conf. limit) high side of the casing trimmed length should not exceed 1.760. So, if the tolerance on your trim process is +/- .010, then you should trim to 1.750 as a target. Few months back I showed a method of modifying the RCBS precision mike to make the distance measurement above. I think Sinclair and maybe some others make a similar gage. To be more accurate, you should temporarily remove the spring and pin of the ejector pin/plunger in the face of the bolt when you do it. This is because a strong ejector spring pin can hold the base of the measurement device away from the bolt face a few thousandths. |
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