Measure Chamber Length and Trim Length Question

[drn1234]

So I am a little confused on trimming to actual chamber length of the rifle instead of just cutting your brass to book specs.

So I measured my .260 chamber to 2.060 using the sinclair gauge insert.

Then I measured about 15 or so of my once fired cases.
anywhere from 2.023 to 2.032 before resizing.

New out of the box Lapua brass measures 2.027 just FYI.

So my question is that it states to trim to slightly under your actual chamber length. But my brass seems to be well under the 2.060 I measured.
So why is my fired cartridge length not longer? Is it because It was only fired once and it will get longer with firings.

Do I trim to an average between the current brass measurements (2.023 to 2.032) to make them all consistent?

Just a bit confused because the book data shows a case length of 2.035. So all of my Lapua brass is well under this already.

Am I doing something wrong. Do I need to trim etc etc.

Thanks in advance.

 

[bglenn]

I measure the length then trim to where they are all the same length with in .002 or .003. Then finish prepping them. They will grow in Over All Length each time they are fired. How much they grow is determine by the sized head-space length to the chamber head-space length. The looser they fit the more they grow.

 

[Steve Blair]

SAAMI max for .260 Remington is 2.035". Your Lapua brass at 2.027" is pretty close. Most chambers, unless reamers are ground to a specific chamber dimension, are generously long. I've never seen it cause a problem if the barrel is cleaned adequately.

 

[bglenn]

drn1234 - I don't know how much experience you have but I want at least .020 clearance between the case neck and the end of the chamber unless it is a bench rest gun. .010 can creep up on you before you know it. I know from experience.

 

[lpreddick]

fired brass is often shorter than unfired. when fired, the case expands to fit the chamber bringing the case length down a few thous...factory chambers are often "sloppy" whereas a tight custom chamber may have very little growth. brass "grows" for several reasons..FL sizing with an expander is possibly the biggest offender, but repeated firing contributes and some case designs are felt to grow because of their design...243 win. if one monitors case length, the shorter the gap from case mouth to chamber end seems good for several reasons. the "dreaded" carbon ring occurs quickly if the gap is long and if ignored this ring can literally crimp a case mouth and pressures go up. a long gap wil add to the freebore and affect seating into the lands. trimmig to the majority case length is safest. i always seem to have a few cases that are .005+ shorter and they get culled.

 

[stool]

right, and always set your sizing die to touch the shell holder....

both of these steps will make money for the brass makers...don't do it.

you have a couple of options.
do as was suggested and trim to some common length.
or
let them grow...., measure each after each shot,so you know how much they grow per shot.
then decide what you want for a case length based on YOUR known neck length( this is about neck length, not case, because you still size based on YOUR CHAMBER)
if they grow slow, say .002/.003, then use a -.005 trim length and trim every time.

drn1234 - I don't know how much experience you have but I want at least .020 clearance between the case neck and the end of the chamber unless it is a bench rest gun. .010 can creep up on you before you know it. I know from experience.

 

[drn1234]

bglenn, I have a decent amount of reloading for tactical rifle but I am now starting to take techniques and processes from the benchrest crowd and apply them.
So I feel like i am starting new again. lol

Thanks everyone I now have a clear idea of what to do and expect.

Thanks!

 

[BoydAllen]

One last thought...just because it is in the Sinclair catalog does not mean that you need one ;-)

 

[mikecr]

I agree with lpreddick, and I keep my trim as close as 5thou to chamber end where I have that control.
It seems to reduce ES. There is less sooting down the necks to ~shoulder, and with this I'm thinking there is quicker/more consistent neck sealing. Well, provided there is not excess neck clearances to negate all of it.

But this should not be bothered with when using poorly designed cases that will continually change in dimensions with each firing.
In that case, and holding excess clearance already, I wouldn't trim them at all. Just chamfer mouths for seating.

 

[drn1234]

Boydallen, LMAO, i love tools!

 

[Steve Blair]

One last thought...just because it is in the Sinclair catalog does not mean that you need one ;-)

[br]
Blasphemy!