First option is send it back to OLy and ask them to fix it - this should be covered under warrenty. Next option, if your impatient and want to have a go yourself is:
First, are/or have you cleaned the chamber - with the appropriate brush? Some AR's with tighter chambers dont like crud.
If the chamber is clean, then you may have a burr. To check, clean the chamber and either use a dental pick or similar object and slowly move it around the chamber feeling for areas that it catches on something or use a quick and look for snags. Also, if there is a burr, it should (most likely) be scratching your cases. So examine a clean new round (to make sure it doesnt have any scratches before you chamber it)and chamber the cartridge, then extract the cartridge and look for linear marks. I realize this is tough in your situation.
Once/if you find a burr and are still feeling like playing gunsmith on a factory warrenteed rifle, you need to polish it out.
Next area of possible problem could be your extractor, remove your extractor and place one of these [url]http://f2.pg.photos.yahoo.com/ph/gunslingerdoc/detail?.dir=/guns&.dnm=orings.jpg[/url] over the spring and reinstall. At the same time inspect your extractor for damage or crap/debris under the rim.
Hope this helps. keep us posted