That sounds like a "T" or "HB" to me 'cause my 541-S barrel isn't anywhere near that diameter. There is also the Government contract target model and I believe its designation was "X" but I'm not sure of the barrel diameter; it is larger than an "S". There were quite a few of these released by CMP a while back. I think I also remember that the Government model was not drilled and tapped for scope bases, only the target bases/sights.
