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Trim length for 300 BO

TexasHaag

TexasHaag

Private
Minuteman
Jul 3, 2022
65
21
Killeen Texas
Greetings
Here is my question about trimming brass, I'll use 300 BO for example, but it applies to most cases.
SAAMI says 1.368 - .020 ok that gives a trim length of 1.348. I'm seeing lots or references to 1.363 that is only - .005.
what's the deal... can anyone explain?

texashaag
 
1.368 minus .020 is 1.348. Anything in between those two max and min numbers would be in spec range.

Most recommendations are to go to the middle which would be 1.358.
 
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If you are seeing case length figures from SAAMI that list 1.368 -.020 it means that the maximum case length is 1.368 but if .020 less that is acceptable. SAAMI does not list trim lengths which is really an arbitrary number. For rifle cases .010 below maximum length is normally listed.
 
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I have been trimming my 300 Whisper/Blackout to 1.355 for about 15 years now.

This means it will fit in all the different flavors of the 300 chamber.
 
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