i have been trimming some 30-378 brass to 2.903". i forgot where i got that number, but anyway, that's what i've been doing. i looked in the Accurate Arms reloading manual and they suggest 2.895".

i bought a chamber length gauge from Sinclair and used it today to tell me the maximum length brass that will chamber in my rifle. i got a reading of 2.946". that's a whole lot longer than what i am presently trimming and even longer if i was trimming according to the AA manual.

is there a problem with letting the brass continue to lengthen, until it gets somewhere closer to the 2.946", before i worry about trimming it?

what effect will it have on my loaded cartridge if the brass is say......2.940" instead of my present trim length of 2.903"..??

My book shows that brass to be 2.913 and to trim .010 under that is exactly where you was!!!

I personally would trim all my brass to that number.

The point of trimming brass lengths is to prevent the end of the case growing to the point that it is crimped heavily to the bullet by the end of the chamber when the powerful camming action of closing the bolt is done. That crimping action has a tendency to powerfully hold the bullet into the chamber, not allowing it to escape with pressure and the result is to seriously raise pressures. This can't happen unless the cartridge length exceeds the length of the chamber.

Shorter brass has never been a problem for me...so I like to over trim just to be safe and so that I don't have to do it often.

I would let the brass grow untill you get to the .010 below the chamber measured length and just keep the brass in lots according to number of times fired and check the cases for seperation as normal.....I would look at the cases when they get to the max length and watch for any pressure sign changes esp. in HOT weather but I can't see where letting the cases match your chamber will cause any problems....those chamber length gauges will tell you correctly and can be eye openers on some chambers!...good luck and good shooting-loading!!