Case length inquiry

[Caretaker]

I've been reloading for about 25 years and have never taken an interest in case length until now, don't ask why I just haven't.  I reload brass no more then 5 times then toss them.  I purchased a Hornady manual case trimmer today at Sportsmanwarehouse (love that store) to get me started at the entry level, if I like it I'll probably get something more upscale, not sure yet but that's always a possibility.  Anyhow, I am in the process of reloading a new batch of 270 WSM for my Sako A7, so with a bunch of Federal factory loads shot once I cleaned them in my Hornady ultrasonic cleaner, resized them then manually checked the length of them all, I was shocked to see they ranged from 2.092 to 2.110, case length on these is supposed to be 2.100.  That's a delta of .018!  I'm not a benchrest shooter but I desire perfection where I can get it.  I'm willing to bet that the variance in case length/neck length has an effect on groups.  For brass that's .008 under the case standard of 2.100 there's nothing I can do about those, but for those over that I trimmed them down to 2.100.  For desired accuracy is it ok to trim them all to the shortest length of the batch that I have of 2.092?  This way I can insure that I remove that variance?  Is there a brass manufacturer that is preferred that is more in line with case standards?  Thank you in advance for your input.

[Wanttohuntmore]

Each shot lengthens the brass.  Some brands seem to stretch easier than others.  I find the more expensive brass seems to stretch less.  However, great accuracy can be attained with cheap brass as well.  I always trim to the shortest length to keep the consistency of the neck tension, and always buy brass in batches of the same manufacturing lot number.  Another thing you can do after trimming, is sorting brass based on weight.  Toss the extreme ones, as they are usually thicker or thinner, contributing to different internal pressures.  Brass consistency seriously affects accuracy.   

[jasnt]

I also trim to size them all the same. If it's a few thousandths short it won't hurt. I'd rather have consistant neck tension and square mouths.    Reload 5 times then toss
That's spendy. I would suggest looking into anealing. It will save you a bunch of $ in brass and if done often enough will keep your neck tension more consistent.

[BULLBLASTER]

If your brass is growing excessively when you fire I would look into your sizing. Bump the shoulder too much and your brass will grow due to the added headspace. Too much growth and you could see some case head separation. When the brass gets longer it isn't the neck that is stretching. It is the case body and then try size it it pushes shoulder back and that makes the neck lengthen. I try to size just enough that it will chamber.
Also you are fine to trim them all .008 shorter than spec as the trim to length in most books is .01 shorter than spec.
This is to make sure that the brass doesn't get longer than the chamber allows. Your chamber may allow longer brass than the spec says also.

[Caretaker]

Thank you everyone, I trimmed them all to the same length of 2.092, loaded a few rounds with Magpro, 130gr Barnes TTSX, starting at 70.5 grains and working up to 73.5 gr, WLRM primer.  I'll see how each of them shoot and work more on the ones that do better.  I think I'm going to like this trimmer, it adds a layer of consistency that I'm looking for.  I'll trim all my other brass with different calibers the same as I am with my 270wsm.  Now I need some range time

[BULLBLASTER]