Trimming Brass. how far to trim?

[champ198]

I have been working on Lad Dev for my 6.5CM.
Figured the CM was the easy button as some say to get my process down correctly so I know what I am doing for other rifles.
Right now I have some loaded up to find my charge weight. Then plan to tweak seating depths.

My question is on trimming the brass to length.
I have about 15 cases roughly that are at 1.922 in length. Max case length by my book shows to be 1.920.
Bought a trimmer as it was one piece of gear I did not have yet.
My question is how far back to trim?
In looking it looks like Min case length is 1.910 Max is 1.920.
Should I just split the difference and go to 1.915?

Its not great brass (Hornaday) but its all I have right now for my CM.
I also do not anneal if that makes a difference.
At least I dont yet.

 

[parshal]

Go 1.910" and never trim again.

 

[stello1001]

Yeah, I'd go to the maximum trim amount that gives you the shortest length specified. This will hopefully get you trimming less in the future. If you think that's trimming too much and don't want to, I guess just split the difference.

 

[Rocketmandb]

I used to trim short, but doing so causes a carbon trap in the area between the end of the case and the end of the chamber. You will tend to get carbon rings in that area. The smaller the gap, the less carbon tends to build up. With a new chamber, I now use a borescope to compare the longest case (post sizing) to the chamber. When the longest case gets really close, I set the trimmer to that length and trim every couple firings.