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Old 06-07-2011, 07:34 PM
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Question Case trimming and trim to length vs Max length

When trimming cases, usually rifle not so much straight walled handgun cases. The manuals have a trim to length and of course the max case length.

Why do they have a trim to length of (.01) 1/100th less than the max length?

Say for .223 Rem the max length is 1.760 and the trim is 1.750?

If using the little Lee trimmers I believe they only trim back to the max length.

Is the trim length to allow for "growth" of the case??
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Old 06-07-2011, 09:31 PM
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I have NEVER trimmed a straight-walled pistol round. Never will. Don't see it as necessary. By the time they've stretched to the point they need it, they're starting to split, and the primer pockets are getting loose. In the case of the 45ACP, they tend to shorten over time and usage.

My Lee trimmers are factory-set to the "trim-to" length, which always seems to be 0.01" below the maximum allowable length. Most are right, but a few have needed to be adjusted a bit.

The bottlenecked rounds tend to grow longer with each firing, which happens faster with full-power loads. If you trim to the recommended "short" length, you should get about five firings before they need trimming again. A well-known ballistic expert, whose initials were Ed Matunas, used to say that after a fifth trimming, the cases were ready for the scrap heap. I have yet to see a case that lived long enough to need TWO trimmings, let alone five.

But of course, your results may be different.
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Old 06-08-2011, 07:00 AM
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Quote:
Originally Posted by OCD1 View Post
Is the trim length to allow for "growth" of the case??

Yes, that is exactly why they are trimmed to that length. I, for one, also trim my straight walled handgun cases, but only once. When I first get them I trim them to a set size so that all of my brass is the exact same length. That way I know that I get the same crimp and same bullet seating depth every time. Is it necessary? Probably not but I like knowing all of my components are the same.
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Old 06-08-2011, 07:10 AM
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I use the Matunas method on my bottle neck cases and cut the to minimum and uniform length from the start.
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Old 06-08-2011, 09:22 AM
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Good morning
+1 On the trim to minimum... trimming cases is by far one of my least desirable reloading activities. I do them in batches.. After 4 reloadings check length of some . But I also dedicate brass to weapons and stay away from max loadings which really do not deliver that much more benefit. I generally figure a need for a max load shows the need for a bigger bore.
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Old 06-08-2011, 04:30 PM
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Howdy

Yes, the idea is to trim to the 'trim to' length. If the cases grow at all, after they pass the Max length, trim to the 'trim to' length again.

Some manuals specify .005 under Max for the trim to length, some specify .010.

Whatever the case, count me as one who has never, ever trimmed a straight cased revolver round. At the pressures I normally shoot at, they simply do not grow at all.
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223, 45acp, crimp, primer

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