I have a precision bolt rifle that has a relatively short chamber.  On my hornady headspace comparator, a once fired 223 case measures 1.460”, which is the bare minimum spec for a 223 chamber.   I have a ton of gold medal match that is once fired through this gun , and I’d like to use it for reloading in my gas gun.

With the once fired cases being minimum spec, should I shoulder bump this for my ar? Fl size it?   What is the maximum case growth that is safe for a 223.

I would full length resize it. You might not need to run you die all the way down, but the die is also going to size the base of the case. Ctg. headspace is just one dimension adjusted by a FL die.

You can take a fired case out of your AR and see what that measures and compare the two. Then try a fired case from your bolt gun into the AR and see if the bolt will close easily. Don't let it slam home, but ease it forward and then use the FA to see if you can get it to close. My guess is it will get stuck.

With ARs it's always best to FL resize. Don't forget to trim the brass, or at least gauge it so that it's not too long.

I would most definitely FL resize, just to eliminate any potential issues.

Then certainly trim to 1.760" or below.  Assuming your AR has a 5.56 NATO chamber and not .223.

Exactly this. FL first pass, period. If it's for a particular rifle/chamber you can size less just for that gun. If you're loading in bulk for multiples either FL size or size to the shortest chamber you've got.

Agreed. First FL resize I trim to 1.750. Every loading after that I measure,  if it is under 1.760 it passes, if not it gets trimmed.

Don't overthink it.

Full length resize as in FL sizing die making contact with the shell holder at the ram up position?

I’m running a rock chucker, rcbs shell holder, and rcbs match master fl sizing die .

As mentioned, FL size even if fired in a tight chamber.  I actually trim slightly below trim-to, so I don't have to trim again next time.  It really only affect the amount of neck that is holding the bullet and a few thou's less isn't going to mean diddly, and they will eventually grow.  Anneal if you are going to load more than a few times.

Full length resize to 0.002-3” shorter than a fired case from the AR. Comparator measurements off the bolt gun are irrelevant to the AR.

What is the maximum the brass can grow during firing and be safe?   If I can keep my die set from my bolt rifle, and I don’t have to adjust it every time, that would be great.   All I’d have to do is use my comparator to measure a once fired case from my ar, and then size it with my fl sizing die set for my bolt rifle.   My bolt gun rounds are getting a fl sizing die bumped to .002”.   So if that works on my ar, I’d rather not touch it.

I also use my rockchucker to size my .223 brass. I set my die up so there is an ever so slight cam over when the ram is all the way up.
Different dies may or may not require cam over to size the brass down to factory specs.
It's best to use a case gauge when setting it up this way.

The way I do it is raise the ram all the way up, screw the die down until it touches the shell holder and snug it up.
Cycle the handle a of couple times just to double check the shell holder is touching the die.
Then screw the die down the smallest amount until I can feel the shell holder bottom out on the die and the handle gets firm but still has a tiny bit more room to move.
We're talking the slightest amount.
You can feel the handle bottom out, then push through until it hits the stop at the end point.
You need to take care not to have too much cam over.
It's hard on the press and you could potentially over size the brass.

Also, be mindful that after full length sizing, your brass that is currently 1.460" is going to get longer.

Ya, you'll never reach the lands with a cartridge that will fit in the magazine in a gun with an off-the-rack barrel.  Not even close  ^^^

Whether chasing the lands actually matters is another discussion.

Thanks man.   I reload precision ammo for bolt guns .   My normal process is decap, tumble, anneal, fl size to .002” bump and set neck tension with bushing, mandrel, tumble, trim, chamfer and deburr.  I have never looked at a saami spec.  I load 80-90 grainers, and have to hog out my mags to fit them.   Bolt rifles are awesome 😎

I’m starting loading for ARs now, and while it seems a lot “easier” , it’s a lot different than I’m used to.

Anticipate setting up the die differently for the bolt gun vs AR or just FL size everything. If you want to precision loads for the bolt gun, keep the brass separated.

Maximum case growth for safe firing is firearm specific. I trim cases to 1.750" after first firing which is a very common trim length for AR brass. Then trim as needed. This is for both precision bolt and range fodder AR.

Since your reloading FGGM, case lengths might not even need to be trimmed. Always measure after sizing (just in case you weren't aware ). What are the case lengths now if you measure a couple handfuls?
In my experience federal seems to run shorter than other brands. LC will always need to be trimmed after first firing.

#1 Idea keep the brass separate from the bolt gun brass and the brass that is subsequently fired in the AR.
#2 Keep track of the number firings on each lot of brass.
#3 Even with case lube in the neck the expander ball will always stretch the brass during resizing that is why you feel resistance.  Some people use bushing dies to control neck tension.  Or a mandrel and bushing die to control the neck tension.  Some brands of dies have carbide expander balls you can  buy as an upgrade Lyman/RCBS/Redding all come to mind.  Dillon rifle dies come standard with a carbide expander ball.
#4 Chasing the landing with bullets other than the heavy VLD type bullets (75gr and heavier for the most part with a few exceptions such as the Sierra and Nosler 77gr OTM and the Hornady 75 OTM) is utterly ridiculous to say the very least.
#5 Unless you have done chamber casts of your guns individual chambers you will never know how much you can let brass grow....  Simple #'s Trim to Length is 1.750 Max Length is 1.760.  That will keep you out of trouble.  
#6 To the OP keep things as simple as you can.  So many people want to buffalo new reloaders with unadulterated BS.

Reloaders have been reloading quality ammo that is safe - accurate - reliable without all the Gobble De Goop some people insist you need.  I have been doing it for 50 years.....no case gage.  Just decent caliper.
No Giraud Trimmer.  No Auto Trickle V4.  RCBS JR Press RCBS Dies RCBS trickler RCBS Uniflow Hornady beam scale.  A RCBS file trim die for trimming.  Sure stuff has been upgraded over the years.  But the press lasted me until the early 2000's.  I still use the powder measure and trickler.

What is the ammo you are shooting to begin with?  Federal and Speer has some pretty short length brass sometimes, at least in their LE lines.  Might be part of why they are so short.  I see on e fired come out around 1.740 from AR’s, or even shorter (if my memory is correct).  Just how they load the ammo….

Speer=Vista=Federal, all under the same umbrella. Yes, their brass can be very short, IIRC I've seen as short as 1.736" or so.