I've had no issues and it's all I shoot.  There's a huge ammo sale at Cabela's in East Hartford, CT.  Bought two 200 rnd boxes two weeks ago.  Their $89.99 a box

I have only shoot Federal XM193 ammo in my SU.  My local shop has the AE XM193 for $89 per 200.
I wasn't sure if all XM193 is loaded to the same spec.  I read that XM193 does not meet SAAMI specs,
hot ammo = Big flash  I guess I will give it a try this weekend.
 
Russ

My two concerns are chamber pressure with the 5.56 (which the SU16 is labeled right on the rifle), and stopping power. With an SUV type rifle, I want the best of both worlds-stopping power and accuracy at a good price. I've purchased the 5.56 rounds today and have only fired .223 Rem up to this point. Still hoping for some field-tested feedback. Thanks for the replies. BTW, I'll probably shoot this weekend to determine for myself how I (and my rifle) like this round.

Quote from big-foot on 11/04/09 at 22:07:20:

 
In reviewing the ar15.com/ammo link, it looks like the xm 193 is the go to round for all purposes. Most of the reviewers maintain a cache of about 1,000 rounds in .50 cal ammo containers. If I'm comprehending correctly, it isn't a match grade round (ok for me, my rifle isn't a match-rifle), ballistically it is stable at 1:9 twist (good for me), it will take big-game with a good sight picture at a reasonable range (still positive), and two-legged cretins will drop on the spot if struck by one of these rounds. I've decided to upgrade from my 200 rounds of xm193 to 1,000 rounds with a nice ammo box to store them in. I'll still buy some Hornady HP strictly for meat, but I think the research dictates a cache of xm193. Any disagreement?

Not that I'm aware of.

Quote from big-foot on 11/05/09 at 11:34:34:

Been there, Done that.   I like the performance of this ammunition, cheap enough to cut paper, capable of doing its job when necessary.

Or carry a bigger rifle.  I have an old (1952) Remington 740 semi-auto 30.06.  I was able to find 10 round mags for it.  Now that's stopping power!!!!  5.56 is perfect for coyote hunting and smaller.  I wouldn't take it deer hunting unless I was in a survival situation.