Case trim length

West Calamus

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May 23, 2019
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texas
Does every one trim back to minimum case length when trimming cases? Is there any advantage to only trimming too half way between Maximum and minimum case length?
 
When I take the time to trim, I trim back to min. That said, one of the attributes of many of the highly accurate cartridges is a long neck. Im not sure that the difference between trimming partially and trimming fully (.005-.010") is going to be a huge accuracy contributor, but I'm sure the benchrest guys might argue that point.
 
The advantage to trimming to the long end of the spec is that you can get a wee bit more powder behind the bullet.
 
It's a good idea to measure your actual chamber case length first and trim cases to .010" short of that measurement.

I've found I get more carbon ring buildup with shorter cases, so I started trimming to .005" under my measured chamber length. I do have to take care that my cases are not over that .005".

It's fine to also use .010" under your chamber, to be safe. If your chamber and resizing die don't mesh well, you will be trimming more often.
 
There are factory chambers with the end of the chamber being very long so that trimming isn't necessary for many firings or perhaps never during the life of the brass. Factory recommendations for trimming a case can leave a .050" to .070" gap between the end of the case and the actual length of the chamber! Unless you used a custom reamer and know the distance to the end of the chamber, it is good to know the distance for each rifle. I suggest that many cases are being trimmed unnecessarily.

Sinclair makes an end of chamber gauge:


video:
 
Sounds like there are many different approaches to trimming. In My loading book for each firearm, I have the actual neck chamber length of that firearm and prefer to trim .010 less than that dimension, as long as all of the cases clean up. I never take more than necessary and only enough to clean all the cases up. I also clean the chamber and bore often so I don't see the carbon problem that some see.

As stated in other post, I do this when my brass is new and gives me the best results. With minimum sizing, normally this is the only time I need to trim during the life of the case. generally I see very little case growth because of the sizing and the pressures I load to. A periodic check as you load is still prudent and recommended.

A dummy case in the die set is a good gauge to use when setting up your trimmer, and applying a blue die to the end of the gauge case and setting the cutter by turning it backwards will prevent you from removing any brass from the gauge case. This keeps the load very consistent unless you have to remove some of the case neck often and then thinning and neck tension may become the reason loads can change.

Also Most of the time, well sizes new cases with minimal head space will normally stay within .003 or .004 thousandths when fired the first time, and if you want to re trim then you could and start with uniform case neck lengths. After that, I rarely have to trim again.

J E CUSTOM
 
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