Ive heard that you need it and then that you dont need it.....what exactly does it do?

THANKS!

Are you serious man? A case trimmer is used to make sure
all of your cases are the same lenght..Sometimes the case
can be too long to chamber,if you have a tight throat in
your rifle..Another is for crimping bullets with the crimping
groove or chantler (spelling)
And to improve muzzle velocity spread..In other words bullet
release from the case.Even a slight measurement in thousants
of an inch make a difference..Your brass will stretch. Some
more than others..I always liked the Lee cast trimmer tool
easy to use and you don't have to set it every time you want
to use it..Simple is the word..I am sure others will chime in
here with there comments.....Read man read

Well, I guess its needed, if you don't want to get into a serious overpressure situation where you could hurt yourself or bystanders. What do you think would happen if you case grows enough to be jammed in the rifling, pressure shoots up.

ok...sorry for the ignorance...is a manual one alright if i cant afford one of the ones that rotates itself?

I can't afford on that rotates itself. Its a dreaded job, but generally only have to do it every 3 reloads or so.

i was told the same thing that it takes 3 or 4 times to stretch as case to the point it needs to be trimed.i would guess every round is different. as for myself after after reloading a case 2 times i generally dont use it anymore but i always check the length. most of the rounds i load are for hunting and it takesa while to get through a batch if i do 100 at a sitting..

if you want a cheap and accurate trimmer get a lee trim guage and get the lock stud that you can put in a drill. you can trim your cases and chamfer and deburr while you are taking it easy in the recliner. just use an old towel, large shop rag or news paper to let the trimmings fall on or your wife will skin you when she gets a brass sliver in her pinkey toe.

If you are a brass rat, like I am, not trimming is like the others said. Crimping a too long case will increase pressures besides groups going every where. I used an old Forrester that I picked up years ago. It's a PIA...but works fine.
Dan

You may not 'need' to trim. Get a Sinclair chamber length guage. You might be very surprised at just how seldom you really 'need' to trim. I hate trimming brass!

http://www.sinclairintl.com/cgi-bin/...amp;type=store

I keep a dummy "trim to length" casing for each cartridge I reload for. With my Forster trimmer, it only takes a moment or two to set it up for the casings you are prepping. Me, personally, I trim after every resizing. I love uniformity. To answer the original question...Yes. I feel SOME sort of trimmer is definitely needed, along with a good set of CALIPERS!!