Fitting barrels to 412-how to?

[rockrat]

Pulled out my 412 this morning to see if I could adapt some 405 win. basic brass I have, to the 9.3 x 74R chamber.  I only get two shots through the gun before the brass starts to seperate.  Seems the neck is chambered perfectly, but the base of the brass expands about .006 on firings as either the rear of the chamber is sloppy or the Norma brass is undersized at the base.  Looked at the gun and it is a 412 action with Tikka barrels.  Don't know if they were fitted correctly, but wonder just how it is done.  Any references to this operation?  Thanks

PS--Just found this site from Marlin Owners--looks pretty good to me

[Drilling Man]

Hey rockrat,

  I've shot a 412 chambered in 9.3x74R a lot, and i've never lost brass because of seperation!  Of course, i only use RWS brass and keep it to decent pressures!

  Before Valmet started bringing 9.3 bbl sets in the US, i had two sets that were brought in from Finland, in the luggage of the president of Valmet USA for me.  I  created a reloading manual for those bbls. and talked Valmet into bringing in 20 more bbl. sets for me.  I sold all 20 of them through the shop i had at that time.

    I do still have one of those first two bbls. to come into the U.S.  but sorry to say, i don't know where my copy of the manual i made is right now.  If i was you, i'd get some RWS brass and load it up, as it's very good quality brass.

  Fitting of the bbls. shouldn't affect the brass, but if the bbls. aren't fit properly, it will trash the action.  I've seen it happen before by guys trying to fit bbls. themselves and didn't know what they was doing.

  Drilling Man