question about new brass size

P

p5200

Member
Is new brass always the proper length or should each case be checked? My Lyman book says trim to 1.750" for the .223 rem. Does all of the brass need to be trimmed to the exact same length if a little over or, does small differences not matter as far as accuracy goes? Thanks! :)
 
1.750 should be OK for the .223. Trim to within a few thous and that will work.
 
I prefer not to trim until after the first firing for standard calibres. There can be quite a bit of difference in dimensional change from case to case once they've been fired.
 
The reason I trim new rifle brass is to square up the case mouths which in most new brass isn't. As Mr Kielly points out there can be significant dimensional change on firing though, so being persnickety about it before it's been fired is likely a little overkill. That being said a lot of domestic US brass is somewhat undersize in both diameter and length, and will only become shorter on the first firing as the case expands to fit the chamber - even if it's FL sized after firing it's likely to be slightly short.
 
OK..... this is a leeedle bit anal, some would say crazy, but for those match rounds I CARE about I've been known to make up an oversized chamber barrel just to blow them out to get them ready to trim up..... And for all my match stuff I short-chamber so that all shoulders must be reset to headspace and have a stack of chambers .002 apart in size for some.

In reality it just depends on your needs. I expect and plan for cases to vary anywhere within .004 for headspace. and .007 or so for length. This for quality brass like Lapua.

al
 
I have found that cases tend to shorten with the first firing.

So, I do not trim until after the first firing.

George
 
I dug up a bunch of older cheap factory loaded .223 brass of different brands and found some of it to measure as short as 1.736-1.737" so, I think I will fire before trimming. What about lightly deburing inside and out before seating bullets? Thanks!
 
I always round the neck with a neck expanding die, either K&M or RCBS, before chamfering new brass. If you do not have a specific die the expander button in your regular die will work. It also makes the bullet seat easier in new brass.
 
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