I got a reply from RRA about information on their uppers. One thing I re-emailed them one was why they recommended I not use steel cased ammo in thier uppers. I'm still waiting for them to tell me. Can someone tell me whats is so Bad about using steel cased ammo inan Ar-15? All I hear is people say they would not think about using steel cased ammo. But why?

I have heard stories it it wearing out extractors, barrels or jamming up the guns.  It has worked ok for me though in every gun I shot it in.

Its kinda bad at the indoor range though, it smells.

I have no experience with steel case ammo in AR's but can tell you the result of using it in pistols specifically wide body pistols chambered in 40S&W. When brass cased ammo is fired the case expands and then relaxes in the chamber as the extraction and cycling process take place with expected results. When steel case ammo is fired the cases do not expand at least not to the extent of brass cases and the result is increased slide velocity which I have seen cause feeding problems as well as an accelerated and increased amount of ejector and extractor wear. I would expect that if there were to be a problem using steel case ammo in an AR it would result from the lack of case expansion possibly causing an increase in bolt/bolt carrier velocity.

Well, the steelcase ammo is cheap, and the QC reflects that.  The loads are generally a little light, and some guns won't run worth a damn at all using the stuff.  Others run through thousands of rounds without a hitch and get their target practice and plinking ammo for $40 a case cheaper.  My Bushmaster don't like steelcase, my buddy's does.  I think RRA was trying to head off a lot of returns on their product based on failures with crappy ammo.  My opinion would be that if you like the value and understand the limitations of the stuff, give a small sample a try through whatever you've got.  If it runs, buy more.  If not, stick to brass-cased for a few bucks more.

Extractors are cheap.  You can buy a few of them with the savings between a case of Wolf and a case of XM193.  Still haven't heard about an extractor failing early due to the stuff though.

My big benefit to running brass is collecting it up for a reloading friend, and getting a small batch of his (wicked accurate) handloads for my trouble.  Oh yea, and my rifle doesn't smell like someone pissed down the tube when I'm done

There could be many reasons. Fact is, while it works for some, it also jams up spectacularly for many others... mostly failure-to-extract. Given the extra force required to extract the fired case, it seems reasonable that extra stress is being put on your rifle. Whether the cost saving is worth it to you is a personal question, but I can understand why RRA and other manufacturers would not want to have to deal with customer complaints about rifles that were damaged or "unreliable" because of this ammo.

Quoted: I got a reply from RRA about information on their uppers. One thing I re-emailed them one was why they recommended I not use steel cased ammo in thier uppers. I'm still waiting for them to tell me. Can someone tell me whats is so Bad about using steel cased ammo inan Ar-15? All I hear is people say they would not think about using steel cased ammo. But why?

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A number of reasons but heres a couple.

1. Some people and companies are just plain "ammo snobs" and figure if it doesn't cost top dollar then its not good enough for their rifle.  Flame away....ya'll know its the damned truth.

2. Some rifles have tighter chambers than others and should only be firing "match grade" ammunition that may or may not be made to tighter specs than general commercial ammo, or military surplus stuff.

Most guns will fire and operate with steel cased ammo without any problems. Far more do than don't.
This fact alone leads me to believe(and I firmly do believe) that its a gun issue more often than not, and not an ammo issue.
My experience has been good all around with all calibers of steel cased ammo in every single gun I own, both new and old production.
I personally would not own a gun that would not shoot steel cased ammunition.  I'd sell it as soon as I found that it wouldn't digest it problem free.  Theres nothing worse than an ammo finicky gun that will leave your ass hanging in the breeze when you need it most.

Try it, if it works great...if it doesn't either sell the gun or pay the price to feed it and hope your ammo supply doesn't dry up in years to come.
In my case, I couldnt sell a gun fast enough if it didn't perform using steel cased ammo.