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Posted: 1/18/2013 4:10:08 PM EDT
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Okay....trimming cases topic ????.
1. For my AR, etc I am okay with trimming a case down to or right below standard spec. I use a Lee tool that helps me trim to the same length every time. 2. For accuracy, precision rifles, etc...this is not how it is done in some circles (bench rest shooters, snipers, etc). Brass/load is built to rifle. For "practical" purposes, how much accuracy will I loose by using a Lee trimmer (one size, standard, etc) vs tailoring the trim length to the chamber, etc. Am I missing anything here or misreading something on building a good round or a more accurate load/round? |
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Its not the "trim" your typically going to tailor its the cartridges headspace you tailor.
Say your rifles once fired case measures 2.505" (measured with a case comparator tool on the datum line to case head) now say a new factory loaded round is 2.495" measured same as above that is a .010" difference So what i do for bolt guns is adjust your FL die so that my resized case is actually .002" less than my fired cartridge IE: 2.503" What this will do is give me a very nice custom fit to my BOLT guns chamber and will prolong case life and should provide increased accuracy. For tactical match ammo in a tactical bolt gun id bump to .003-.004" for a little more "dirt" room. For my AR15 that i use for ground hog hunting i do the exact same process except i bump .003-.004" of course after all sizeing is done you then trim the case to a uniform length and do whatever brass prep you see fit. I hope i helped and didnt confuse you more 
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You only need to be concerned with case lengths being consistent for crimping if you chose to do so.
The two things as far as length that will concern you the most are headspace as already mentioned and jump length. It's is the length between the beginning of the rifling lands and the o give of the bullet. For me it is important that the seating die. Stem only contacts to bullet just infront if the ogive. This will make sure that different meplates lengths do not effect jump length consistency. |
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Trimming for safety is a given, because a case that is "just a little" too long can cause things
to happen that are not good. It IS conducive to accuracy too. Having the same neck length and the same extent of work (chamfering) to all of the necks in a batch of ammo will get you a lot closer to having the same level of neck tension on each bullet. This gets you closer to having the same pressure level in each cartridge to move the bullet from the case. Each bullet is closer to the same velocity as it engages the rifling and as it leaves the muzzle. That's all good stuff. |
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