Can a shot-out AR15/M16 barrel be drilled out and relined to create a dedicated upper for my Ceiner unit?

BTW, if this works, the barrel will be plainly marked "For .22 Long Rifle Only."

A poster on the main AR Board said the barrels might be too hard to drill out.

Does anyone have any thoughts or experience on such a project?

Regards,
Mahatma

This is just my opinion -- let somebody else do it. Try American Manufacturing -- they have done this for a few people here on ar15.com.
Go to [url]http://www.american-manufacture.com/[/url].
I did it once and don't plan on doing it again. the piloted drills cost a lot (at Brownells) and if the barrel is a shot out GI barrel it is most likely chrome lined and 4150 steel (very hard). Even with a softer commercial barrel if you don't have good equipment for doing this work you most likely will either burn up the drill or break it. It would be cheaper in the long run to have "American Manufacturing" do it.
You might first try E-mailing them since the only time you can get them on the phone is around lunch time (don't let them know I told you this).

Edit to add:
Remember that they are a gunsmithing business and most are backed up a bit in orders. It might take a little time for your barrel to be completed.

It might be easier/faster to just get a replacement barrel.

I just got an M4-profile .22 LR barrel from Fulton Armory for $199.  It looks and shoots great. 3/4" groups at 50 yards with open sights.

Slash has a good Idea there -- in the long-run it might be quicker to go to Fulton armory or Kuehl Precision. Kuehl's runs around $190 for an M4 profile barrel -- the big difference with the Kuehl is you don't need the chamber adapter, the down side might be you'll need to modify your Ciener rail ends so they slide into the Kuehl barrel. Due to the modification the Ciener won't work as originally designed back in a standard .223/5.56mm AR.

I have both kinds of barrels and can't say which I like more.

The Fulton barrels are designed just like the Keuhl barrels.  No chamber adapter, and you have to grind the 'ears' off on the inside of the rails. However, you can buy replacement parts from Ciener, so you could still use the kit in a .223 weapon.