If you are talking about the SM1 barrel kit, you can order them from Sanchez Machine and have him taper the end to accommodate the bolt. 'splattttttt' had it done to a barrel kit and I believe his review was quite favourable.
Newer carters have a ~1.5" insert, similar to a Scepter, but shorter. These would require the end of your barrel to be bored, similar to having it bored for Freaks. The end of these inserts are then tapered for the bolt as well.
You will need work done to your barrel for the inserts, but you would require a new barrel for the SM1 kit (an SM barrel at that...) as they thread into the back.
Here is a review of the SM barrel kit, note the tapered ID: Sanchez Machine barrels...
I am sure Carter will sell you the new insert kit, you will just need to send your barrel to someone (Carter or otherwise) to bore it out.