When to trim cases??

[elkstalker300]

I reload for a 300 rum and have 3 times on the cases. Now they are starting to exceed the trim length (2.840) in my Sierra loading book, but are still under the case overall length (2.850). Question do you measure the length before resizing (FL) or after???????

 

[Fulldraw™]

Measure your over-all case length AFTER resizing!

 

[kraky]

It's important to understand why you trim a case. Then it becomes obvious. You trim it to keep it from being so long that when you chamber your round the case is so long that it gets pinched down onto the bullet keeping it from releasing during ignition. This causes a big spike in pressure.
I have a set of these and really really like them.....
http://www.sinclairintl.com/cgi-bin/category.cgi?category=RESDTCL&type=store

I've found that many guns I own have way more generous room than saami spec. I have a couple weatherbies and a savage that just plain never need trimming before the brass is shot because they have over .030" extra room beyond saami. One insert works for many calibers. They are a real eye opener and have saved many hours of trimming for me.
Unless you have them please be sure to trim before final loading (after sizing). I personally know a friend that sheared a lug on a bolt because he wasn't trimming. It could have been much worse.

 

[jmden]

2nd Kraky. Don't just follow the book blindly. The Sinclair chamber length guages are great.

 

[Jim Hundley]

Kraky +1!