I have a Tikka 55 which was originally a .17. When the bolt is closed the lugs only engage about 1/2 the width of the lugs. I guess this was all that was needed for this cartridge and it allows for less rotation to open and close the bolt. The bolt does not rotate 90. Has anyone used this for more robust cartridges i.e. 223 class?

Ian I own two Tikka 55's a 22rem and a 308win and also have had them in 22/250 and 17. The 22/250 is owned by a mate and is now a 7mmIHMSA none of us have had a problem with them also another mate had one turned into a 6mmppc bench gun (worked well). So you shouldn't be concerned about action strengh.

I have one in .243 and its been fine except lately I notice the extractor spring is getting a little weak.

The difference is that these actions with a different bolt do engage lugs completely where this one does not. I guess my question pertains to this specific bolt.