Most 5.56 chambers need a bit of work (polishing) to get them to function reliably, and they're meant to be the most generous.
For those that don't know, 5.56 generally had about .125" bullet jump.
The throat normally runs at .2242" so it is generous all round.

One of the more popular "match" chambers is the renouned .223 Wylde.
This is actually larger than 5.56 in most critical area's but has a shorter throat and therefore less jump.

Another one is .223 Rem "match".

I have reamers for all three and they all work. In fact, some of the most success and reliability has been with the .223 Rem reamer.
The rifle I built last year with a Wylde chamber didn't like RG at all until I had put somewhere in the region of 500rds through it. Now it eats RG like there's no tomorrow.

But.........................................if you are only interested in a range day rifle, you won't be unduly concerned about the final accuracy details, even though the gun is capable of far better accuracy than most shooters can achieve.
It's the ammo that lets them down, not the chamber.

Actually, after building a lot of guns, I am of the opinion that the extraction problems lie in the neck and here is where the extraction problems start.  That and incorrectly sized cases.

Now.................Rifles that do have extraction problems with RG ammo, usually don't have them with other types of NATO ball, and that is because RG is a little different regarding the pressure curve.
I have Lake City and Hirtenberger ammo as well as having shot various other types of ammo through some of my "tightest" chambers and only ever had problems with RG.
thee are other types of RG and some of the newer spec stuff doesn't have the same problems.

I have also run some extremely hot 80gn loads with pressures so high that primers have been blown completely out of the cases and still managed to extract them and this has led me to believe that another of the culprits is not only the unique RG pressure curve that is designed to operate the SA80, but the fact that RG cases are rather thick and therefore don't contract sufficiently after they've been fired and cooled.
MEN cases have the same problem and so do the older Lapua .223 brass.
A good chamber will digest all of these but there is always a payoff.

If you want a gun for casual range days and the odd bit of competition using ball ammo and te occasional reload, then 5.56 is fine.
If it'sfor more dedicated shooting with only the best ammo you can feed through it, then I'd recommend talking to your gunsmith and then choose a "match" chamber

Mark

Headspace is not important

Quoted: I could do with my M4gery sorted to handle 5.56...... It's chambered for .223 at the minute and I have nearly 500 RG that I want to play with..... ....... It seems to have been consigned to the back of the cabinet really and tends only to go up to the farm when I have some PRVI shite to push through it.... Anyone game?

ermmmm....cough........im inbound

So far I'm looking at: Recce Carbine, A2 stock, flat top upper, 1/7 twist & Leupold 4-14x50 LRT Just the forend arrangement to decide on and some iron sights and I'm sorted. Richard - Still no joy with the 650

What's wrong with the 650?

As for the fore-end, it's gotta be a Larue or Daniel Defense
Midlength would be nice with a 16 incher

Mark