Case Trimming

[TN Shooter]

New to precision reloading and was wondering if someone can explain the process to determine what my case length should be trimmed to? Do you just trim to SAMMI spec or is there a more detailed determination of length. I am shooting a 6.5 Creedmoor and using the world’s finest trimmer which indexes off the shoulder. I bump the shoulder back .002 during resizing. Also, how often do you trim? Thanks.

 

[PaC1776]

I trim to whatever the "Trim to length" is stated in my Lyman manual.
Max case length per my Lyman manual for 6.5CM is 1.920". Measured from case base to case mouth. Trim to length is 1.910".

Trim (if needed) after you resize and never trim a case more than 4 times. Cases that have 4 trims on them are likely becoming rather thin at the web and nearing case head separation situation.

You could get a few firings on brass before it needs to be trimmed.
I use a Wilson micrometer trimmer. It's very accurate because it indexes off the case base.

 

[SND]

I trimmed right in the middle of the saami spec with my 308. I run cases through the giraud every firing because I reload on a progressive.

 

[PatMiles]

I've determined the length of my chambers, 6.5 CM & 6PPC, with Sinclair inserts. You do have to trim back a piece of brass per the instructions. Then you know the length of your chamber.

https://www.sinclairintl.com/reload...s/sinclair-chamber-length-gage-prod32925.aspx

 

[padom]

Depends what gun/caliber...

For my custom bolt guns I fireform virgin brass, bump shoulder 0.0015" and trim to book trim length so everuthing is inform...Then I don't trim again till I am at book max. How many firings it takes before the next trip depends on what caliber, if your bumping shoulders or just neck sizing.

I bump my shoulders .003 and trim to book trim length after every firing for my semi autos.

 

[dannySH]

I trim all my new brass to "trim to length" then I won't do it again until they get the maximum trim lenght, usually after 4-5 fires.

 

[Deleted member 10043]

Half between SAAMI max and min. When a batch exceeds max. Never heard of don't trim more than four times. Some anal people trim every time.

 

[TN Shooter]

If you wait to trim until you get to max length, isn’t the neck grip varying with the length? I figured you would have to trim every firing to keep consistent but it may not be enough variation to notice. Thanks for the replies.

 

[Deleted member 10043]

It gets lost with all the other immaterial factors or noise with reloading. But some people are anal so different strokes for different folks.

 

[Torchy]

If you wait to trim until you get to max length, isn’t the neck grip varying with the length? I figured you would have to trim every firing to keep consistent but it may not be enough variation to notice. Thanks for the replies.

Always wondered this too.

 

[McCrazy]

I trim to a length halfway between the "trim to length" and the "maximum length" once my brass is starting to reach or exceed maximum length. This helps ensure that I am fairly consistent, not trimming too often, not removing more brass than I need to, or exceeding the maximum length which can be dangerous.

When you exceed max length, the neck of the brass can extend into the area of the chamber that is not meant to accomodate the thickness of the brass. This may cause the barrel to squeeze the neck into the projectile and cause an over-pressure situation (possibly catastrophic) when you pull the trigger.