Neck Length?

[dbshabo]

How much length should be left open in the chamber to allow for neck growth? I'm just getting started loading 6.5mm Creedmoor and have found out the distance from bolt face to the end of my chamber. Now how much should I subtract from this measurement to determine the max case length I should screen for before I trim the necks?

Shabo

 

[243winxb]

Brass maximum trim length

.010" shorter. Or no longer than the listed maximun trim length. There can be shoulder set back from the firing pin strike (223) allowing the neck to go deeper into the chamber. I have to wonder if the brass then would headspace on the case mouth??? Or pinch and raise pressure???

 

[gamestalker]

In your reloading book, find the trim too length for that brass, that is what you need to trim it too. Measure from the case head to the mouth to determine the length of the brass, and how much needs to be trimmed off. Also, when measuring, and, or, trimming brass, always do it after the brass has been resized. If you measure, and, or, trim prior to resizing, you'll find that the brass grows after having been run through the resizing die. Even if you are only using a neck die, it is going to change the brass length.

FYI, letting your brass go beyond the published SAAMI maximum case length can in fact result in excessively high pressure spikes. This is do to the case mouth getting pinched in the throat when the cartridge is discharged.

GS

 

[918v]

There's not going to be .010" of shoulder setback from a firing pin strike. Most factory chambers are .035" or so longer than the recommended trim length.

 

[homatok]

Brass grows on firing. How much it grows depends on several things, such as the metalic composition of whatever brand you use, sizing of the case between firings, presure of the load used etc. etc. As noted above, look in the loading manual for the maximum length and (if necessary) trim to ten thousandths below that figure. Brass does not need to be trimmed/retrimmed until it is at or close to the book maximum. Assuming a bolt rifle, neck or partially sized cases will require trimming less often than cases that are routinely full-length sized.

 

[rcmodel]

SAAMI MAX case length is 1.920".

Trim Too length is 1.910".

We will assume your chamber is SAAMI spec.
So those are the measurements you should use for your brass trimming.

rc