5.56X45 in a Contender?

[cheapshooter]

I have read a lot about the 5.56X45 military round causing high pressure when fired in a 223 chamber. I was wondering if anyone has shot the military surplus ammo in their Contender 233, and if it works without problems, and how well?
I just ordered a 223 barrel, and my loading bench is not up and running, so for now I'm stuck in the already loaded world. I have a lot of 5.56X45 that I shoot in my AR, and maybe a little commercial 223 so I'm just wondering if I should go get more 223 instead of using the 5.56.

[Bugflipper]

Never a problem out of the 5.56 here. My barrel is a tc factory match 14". I have had nato 55 gr and 62 gr through it quite a bit. I have also ran a lot of steel cased, zinc washed silver bear 62 gr hp russian ammo though it. Still shoots fine. As for pressure, of coarse no damage to the barrel, but never had a flattened primer or anything either.

[mcwoodduck]

I have had small problems with mine.
I even had problems with 223 marked ammo that had FMJ bullets.
Anything with a 223 head stamp and a sporting or target bullet was fine but watch out for anything with a heat crimp and FMJ bullets.
Minor problems opening the action after shooting with my 14" barrel.
Never tried them in the 16.25" barrel after the problems with the 14" and since I have a number of 223 riflesit was easy to reach into the ammo storage and grab stuff for another rifle other than my AR.
At one point I looked at going to the 45 grain HP bulk box from UMC as my only 223 round as it works in all of my rifles/ short rifle and sighted in my AR with them.

[35ISIT]

The 5.56x45 military stuff was "warm" in mine. I shot some up to get cases and had sticky extraction. After fireforming loaded and shot fine. Individual chambers behave differently. I suppose you could have one "tight enough" to damage a gun.