after reading posts for the last several days , i am about convinced it will be state arms or armalite . but i was also pondering a short cut , whats the opinion here on 50 cal. uppers ? concerned about putting this kind of beast on my lower . also would anyone lower be better than another ?

Don't use a Hesse/Vulcan lower.

It would be best to use a forged over cast as the forged will be stronger. There really isn't any stress put on the lower, it's mainly used for just the trigger. From the posts that I've read from owners it seems they haven't seen any wear on their lowers.

It's just me, but I'd save up a few more bucks and get a complete rifle rather than an upper. It seems that a lot of guys spend just as much building up an upper as they would have just to bought a Serbu in the first place.  

jeep 29 , what do you mean exactly , by building up , i was under the asumption that all ya had to do is add a scope and lower and off to the range . what other expenses are involved ? 50 shooter , i have a colt , olypmpic arms , and dpms lowers , are any of these stronger than the other ?

I think what Jeep means by the build up is having to buy a lower and changing it from the base configuration. If you have a lower and stick with the basic upper your okay, when you have to buy a lower and want a different bbl length, stock, match chamber.... This is when the price will exceed just buying a complete rifle.

I'm not a AR15 expert but the lowers that you have will work, you might have to add a stronger hammer spring for reliable hits on the primers. One of the guys I shoot with just received his UltraMag-50 upper, can't wait to get out and try it. He's going to use a DPMS lower that he has.

great , would love to hear the results .

I'd like to hear how the ultra-mag does also.  Real appealing to me w/ that 3 round mag.  I just don't like single shots that much.

Make shure you give us a range report on the mag 50 cause it is a badass looking upper and no one has done a report on one yet.