Some good advice on how to remove the barrels has been given here. The only thing I will add is that I use drywall tape wrapped around my barrel and action to 1) get grip and 2) prevent marring. I am 5-5 so far using that .
To answer your question about what bolt faces go with what cartridges, here is a very brief summary in regards to Tikka actions only.
- 0.378" bolt face: This is for the 223 family of cartridges (223, 6X45, 7TCU, etc.). It uses .223 magazines and a short bolt stop (bolt release).
- 0.445" bolt face: This is for the ARC/Grendel/PPC family of cartridges (22 ARC, 6ARC, 6.5 Grendel, 6 PPC, etc). You can also use it for 6.8SPC, however it will be slightly oversized for that as the 6.8SPC bolt head is 0.422". Tikka does not make a factory bolt in this size. In order to get it, you will need to have the 0.378" bolt opened up, or have the 0.473" bolt modified with a bushing, both of which can be done by a good smith. For these cartridges, your best bet for reliable feeding is to put the rifle in a chassis and use Accurate or MDT magazines designed for the ARC/Grendel. Short bolt stop.
- 0.473" bolt face: This is where we can have either short action or long action cartridges. It is the most common of the bolt face diameters and is used for the 308/Creedmoor and 30-06 family of cartridges and all of the variants thereof ( all of the Creedmoor cartridges, .243, .260Rem, 7-08, 358 Win, 338 Fed, all of the BR family, 25-06, 280 Rem, 338-06, etc). The difference is whether you use the short action bolt stop and magazines (308 family) or the long action bolt stop and magazines (30-06 family). There are plenty of wildcats that have been developed using this bolt face diameter as well.
- 0.540" bolt face: Also known as the Mag bolt face. This is for the belted and non-belted "magnum" cartridges, such as the 7RM, 300WM, the PRC family, etc. For these, it is most common to use the long bolt stop and long action magazines, even though the 6.5 PRC is billed as a short action cartridge. It benefits from loading it long.
There are a couple of bolt face diameters larger than the 0.540", but they will not work with Tikka actions. If you want a more comprehensive list of what chamberings will work with each of the bolt faces, a bit of Google-Fu will lead you down the right path.