is it mandatory that you FL size new brass before your first firing? I kneck sized it all but wasn't sure if you have to FL size new brass. As far as i'm concerned, if it's new and fits in your rifle and there are no dents, whats the purpose?

IMHO none

They pull this brass from the same hopper that they turn into factory loads, as long as the case necks are not out of shape I don't see what you gain, I have tried it both ways and the accuracy has not changed nore has the FPS by FLS or not.

Nope

I resize the necks with a Lee Collet Neck Sizer and go for it. Don't trim until after the first firing.

New cases are undersized and Full Length Resizing is not necessary. Definitely do not need to push the shoulder back any. Typically the shoulder is .004" back or more from where the shoulder will be after you fire it.

For example these measurements with a Stoney Point Head and Shoulders gauge on Nosler brass:

30-06 Sako - new case 4.038", once fired 4.042"
30-06 Mato - new case 4.038", once fired 4.045"

That's pretty far considering when I use the Redding Body Die to PFLR, I push the shoulder back .001" to relieve the crush fit.

What woods said! If the necks are geeked up I just run em far enough into the die to get the expander in and out to true up the neck, then neck size em.

Good shooting--D.

It's not manditory but occasionally it will save you much grief. We talked about this on another thread were someone had loaded several hundred rounds only to find out on a Varmint hunt that they wouldn't chamber in his rifle.
I like to FL size because every once in a while it will make a difference. It's just one less thing I KNOW I won't have to worry about.
I also trim them just enough to square the mouths and make sure that they all are the exact same length. I often use a primer deburring tool that set's depth off of the case mouth. I have an RCBS power trimmer so trimming isn't that big of a chore and with the triple cutter it chamfers and deburrs them at the same time anyway so it doesn't really take longer than chamfering and deburring them alone by hand.

Ok, thanks guys. That's what i figured. I couldn't really think of a good reason to, so i loaded up 20 rounds to test out friday. Can't wait to test out the TSX!

Until recently I never resized brass new brass before reloading. I recently bought a bunch of new brass with the necks so large I had to size before it would hold bullets.

the necks of my brass have never been uniform, they had like dips in them, so i just neck sized them and they look fine