Can it be done?  One 1911 with two different calibers (.45 and .40 s&w)?  I know certain manufacturer sells 9mm, .22lr configuration.  Reason I ask I'm about to give in to a buddy's arm twisting of getting a 1911.  I've shot a 1911 before from another buddy.  Sweet pistol to say the least.  I recently bought .45 and .40 s&w dies now all I need is the 1911.  

Not really practical.  Problem is that the frame mounted ejector is in a different place for the two calibers.

There is a caliber conversion you can do: .400 Cor-Bon.  Uses necked down .45 cases, with 40-caliber bullets.  But that's not what you are looking for.  You want to be able to use factory ammo.

Save yourself a lot of grief.  Just get a second gun in .40.

Quoted: Not really practical.  Problem is that the frame mounted ejector is in a different place for the two calibers. There is a caliber conversion you can do: .400 Cor-Bon.  Uses necked down .45 cases, with 40-caliber bullets.  But that's not what you are looking for.  You want to be able to use factory ammo. Save yourself a lot of grief.  Just get a second gun in .40.

   Well so much for that idea.  Looks like two pistols it shall be.  Thanks Milquetoast.

It can be done if you have rampped barrels and dont mind swaping ejectors out when you want to change cals.  All you do is dont pin or expoxy the ejector in place.

You will need frame modifications for rampped barrel.
2 new barrels
new slide complete
ejector

Cost effective, NOPE. Even iuf you wanted to change over a 1911 from 45 to 40 your cost in parts less gunsmith fees would just about add up to a new 1911.

I had a .45 swapped over to a .40. Here`s the story. I had a Nowlin barrel in a stainless Loaded Springfield. It split the barrel, sounded like a squib load, sort of a "poof" and no bullet hole. It split between the lower lugs near to the end of the barrel.
I bought an STI lower and had the SA slide fitted to the STI frame. I had another Nowlin .45 barrel sitting on the shelf so I had it installed.
It was a good shooting gun, I even won CDP SS class at our IDPA regional match 2 years ago with it.
Not to long after that, It split another Nowlin barrel. I got a check from Nowlin for the cost of the barrels. I bought an STI slide and had my gunsmith fit it all up with a Kart barrel in .40.
I like the .40 and I like the way it all shot, so I had one built with the tactical rail frame built earlier this year in .40.