Can this be done without modifications?  I want a .308 upper and already own a standard AR15 lower and want to know if I can combine the two.  

I'm a newb so take it easy on me!

Thanks

Unfortunately, no.  The .308 (assuming you mean .308 Winchester or 7.62 x 51 size) will not fit the STANDARD lower for the AR-15.  You have, essentially, two options:
1 - purchase a platform sized for the .308, such as the AR-10, LAR-10, BAR-10, LR-308, FN-FAL, PSG-1, MSG, to name a few.
2 - The MGI (read this LINK) lower with the M14 mag, plus the MGI upper ...

.308 magazines and recievers are just a LITTLE bigger than .223 magazines and recievers.

Wouldnt quite work

Quoted: .308 magazines and recievers are just a LITTLE bigger than .223 magazines and recievers. Wouldnt quite work

What if you used a rubber mallet and some CLP?

Thanks for the info.  I meant to clarify with 7.62x39, sorry.
If I can't then how can DPMS sell this
www.dpmsinc.com/10Expand.asp?ProductCode=BA-A2-762

I'm a little confused now!

Quoted: Thanks for the info.  I meant to clarify with 7.62x39, sorry. If I can't then how can DPMS sell this www.dpmsinc.com/10Expand.asp?ProductCode=BA-A2-762 I'm a little confused now!

Ah, young grasshopper. the difference is in the details.  The .308 we mentioned was 7.62 x 51, whereas the one you mentioned is 7.62 x 39  Two VERY DIFFERENT critters.  The x 51 is the big round that is also called .308 Winchester and is what the old M14 fired.  The x 39 is the smaller round of Russian heritage, which is what the AK-47 fires.  The 7.62 x 39 can be fired from unmodified AR-15 lowers, you just need the proper magazines (stock .223 mags will NOT work with the larger diameter of the 7.62 x 39).  That is why we asked if it was the x 51 or x 39.

Now, Lumpy and John, take a look at the MGI link.  No longer is a hammer and shoe horn needed.  Mack got a little busy and his modular lower will take M14 mags ... just swap out magwells and you are in business.  I got to see the prototype last year and have had to walk around with my mouth shut for MONTHS until they released it at SHOT in Feb of this year.

I am waiting to see what you come up with for the QCB. I had been bugging Tom about them making a .308 upper and even suspected that that was what was the surprise for the Shot Show and boy was I surprised when I saw it. I can't wait to get my hands on the Mgi modular ar system, and to see what you and Tom are working on.

http://ar15.com/forums/topic.html?b=3&f=121&t=274179&page=1&#-1

im tryin to find out this myself,
if all else i may call dpms today and find out 100% sure