First off thanks for reading my question. I have tried to hunt down the answers to my questions for weeks now with no luck. forums, google, youtube etc.. heres my basic situation I started reloading ammo in February. Basically just took data and messed with a few charges and my gun was ok with it. then I bought some factory match grade loads and I've been consistent at sub 1/2 moa groups. I wanted to duplicate the winchester ranger ammo 69gr sierra match. obviously you cant get all the info and factory loads are headspaced to sami spec. my question is simple whats the best way to achieve proper headspace for my rifle during resizing. heres the break down of some of my instruments and data. any help would be phenomenal I'm kinda at a stale mate here..
Rifle:
(Frankenstein style AR-15)
Noveske 16" MOD 0 556 1/7 match barrel
Battle comp 2.0 compensator
harris full auto bolt
Jard 4.5 single stage trigger
Leupold AR MOD 4-12x
Mil spec forged alum upper and lower

Reloading equipment/data
Lee signature breach single stage press
RCBS AR series 223 small base dies
Lee quick change adapters
RCBS Headspace micrometers
set of calipers, digi, scale etc..

basically my questions are:
-Can I only resize the brass from my weapon?
(reason I ask this is because I noticed my
brass is .0035-.0045)
-Now if I take random 223 pieces say .001 and I need a headspace of .0025 I cant press that its lower than what I need correct?
-So are you able to bring headspace up or only down towards sami spec?

So in a nut shell I'm trying to set these dies up but not sure if I'm doing it wrong or if by using all sorts of used brass with different measured headspaces I'm not going to be able to get my desired numbers. also how accurate are these dies I dont expect the casings to be dead on everytime but not off bylets say one case is .004 next is .002 etc...

Welcome.
First off, to get the headspace correct for YOUR rifle, as you have in your possession a set of headspace gauges, you measure a fired case and take note of it, then size a fired case with the die set to the instructions, if RCBS, the shellholder HAS to touch the die with a case installed and the press MUST cam over on the top stroke, then you adjust your FL Die in if it's too short or out if it's too long. You want a minimum measurement of .002" UNDER your fied cases, and a maximum of .0035", to get good case life.
The amount of headspace helps with bullet alignment, but in regard to accuracy, a good powder burn and concentric necks go a lot further for this.

Hope this helps.

Thanks for the reply it definitely helps. I have a case gauge and measured 10 of my cases months ago and concluded my .002 under would be .0025 so I'm trying to make these consistently. So what you're saying is throw a spent case int the sizer die adjust so it just touches the shell holder and my press is at a full stroke. then remove the case and measure and adjust accordingly?

You might want to move this question over to reloading.

If your ammo is to fired in only one rifle set the headspace .002 short compared to that chamber.

If your ammo is to be fired in multiple rifles set the headspace to the SAAMI number.

I have found the best tool for this is the Hornady case (headspace) gauge that attaches to a set of dial calipers.

To get exactly the same headspace on each case, size very slowly and let the press dwell about 3 or 4 seconds at full stroke.
Lower the ram a little and rotate the case 180 and slowly size again.

They will be exactly the same.

You must separate different brands of brass they can have different volume. Kepp record how many times you reloaded your brass and if its shot in your own rifle. You can use other shooters brass if you full lenght size it.

Use your RCBS gauge to adjust the sizing die downward until your lot of brass (yes, you should segregate) is shortened to ~0.002-0.003" less than the fired brass. If your sizing dies won't allow this, you must take a bit of material off either the bottom of the sizing die (hardened) or the top of the shell holder (probably not hardened) and adjust the die until you get the desired sizing. As one poster said, you can keep adjusting the sizing die down until you feel the shell holder contact the die and feel the handle snap over center.

That's how I do it, using the RCBS gauge.

Clarence

Great you guys have been a great help I'm gonna give it a go this week sorry for the misplacement of this thread as it is my first time I appreciate the help. I understand all of your advice however if a case is say .001 and I need it to be .0035 thats not doable is it? basically can the press raise the headspace or only crush it down and lower the number.. this will set a lot of confusion straight with me. I will stick to once fired from my rifle first and see what happens.

The press can only make your brass shoulder shorter(headspace bigger) the lenght of the neck becomes longer then you do it. The easy thing for a beguinner is to adjust your die to have contact with the shell holder and dont worry about it.Your reloads will work easyer in a autorifle then its full resized. Then you have experience and well functioning reloads you can think about reducing headspace and other small changes.

A FL die pushes the shoulder forward, then back once it makes full contact with the die. I don't mess with AR's, but in a bolt gun I want positive headspace I.E. resistance when I close the bolt. Everything is neck sized until I can't close the bolt, then gets a slight bump.