.338 Lapua trimming question

[Shooter88]

Hello all, I am reloading .338 Lapua, and I bought a Sinclair chamber length gage to measure my chamber and trim my cases accordingly. I followed the instructions that came with gage, and was able to get the exact dimensions for my chamber. The instructions said to trim the case mouth .024" SHORTER than what the chamber is to allow room for the case to expand so that it doesnt over-pressurize.

This is what kind of gets me nervous. For those of you that do this with their cases, is .024" enough? Should I trim more off, or is that amount way more than what is actually necessary?

I know this might make me seem paranoid...but this is the first time I've ventured away from the standard set by the re-loading manuals, so I just wanted to check to be sure.

[Trakker]

I'll take a crack at this, I'm reloading match grade 308

I assume your chamber is cut to min SAAMI specs then you want your brass to be about .010 shorter than the chamber so you don't jam the cartridge into the throat. There needs to be some tolerance since you don't want a compression fit.
You don't want the bullet flying unsupported too far so you can seat the bullet long and into the lands. This can definitely cause pressure spikes.

The case will always stretch as you resize and shoot. Neck sizing only will minimize it and make the brass last longer. Repeated firing will keep using the shoulder forward and "flows" the brass ever so slightly. This is where a body comes in play and reshapes the body and shoulder.
Just a reminder catridge head spaces off the shoulder. In some cases with tight chambers, the taper also holds the catridge in place.




Sent from my iPhone using Tapatalk