Pardon my ignorance guys and gals, but I'm still very new to the AR community and I've got an FNG question.  I have a Colt LE 6920 carbine that I love, but I'm dying to get an upper reciever to make it look like an old CAR 15 for fun at the range.  Bushmaster is the only company I can find that sells the CAR 15 upper with an 11.5 inch barrel with a pinned 5.5 inch flashhider.  Do any other companies make these uppers?  

Can I use my Colt lower, charging handle, and bolt carrier without any reliability problems with this upper?  What should I be looking for in price and where is the best place to run across one of these?

Thanks for the help.

Keep what you got, thats like trading a Ferrari for a Pinto.

Combat Jack, I'm definitely keeping my LEO upper for work and serious use.  I just wanted the CAR 15 upper for grins and giggles.

Model1Sales.com has them also (XM-177), thats where I gots mine.