Is that a colt upper by chance? If so there is a bushing that will make that work.
http://www.midwayusa.com/product/59...apter-bushing-315-to-250-diameter-ar-15-matte
You can also have the lower drilled out to take the large pin for a more permanent fix.
http://www.midwayusa.com/product/59...apter-bushing-315-to-250-diameter-ar-15-matte
You can also have the lower drilled out to take the large pin for a more permanent fix.