For those who have made the conversion, did a simple barrel switch work to convert a model 70 300 rem ultra mag to 404 Jeffery? Did the bolt face need work? Feeding issues to resolve?
Thanks.

There may be enough slop in the factory supposed .532" boltface of the RUM (max brass spec) that nothing needs to be done to fit a 404 Jeffery brass rim.
With max spec of .5429" (CIP) for the 404 Jeffery rim max brass spec and .5449" as minimum spec for the chamber diameter at breach face,
and actual measurement of Norma 404 Jeffery brass rim of 0.539",
a tolerance of +.005" might occur in the factory rifle boltface, whether RUM or Jeffery,
giving the RUM a boltface capable of .539" rim diameter.
Do the conversion.
It is one of the simplest and best.
Ask the smith to be sure the boltface diameter is big enough to handle the 404 Jeffery brass.
Mine had to be opened up just a tiny bit.
All well and good.
Must not have been Monday morning or Friday afternoon in Connecticut when my RUM action was made.
No feeding issues.
Just rebarrel and make sure the boltface is not too tight.

my only advice -- make certain your dies, reamer, and headspace gauge all use the same datum.

Thanks for the replies.

You could talk to Mike at Bijou Creek Customs. He did one for Ernest (JudgeG) and is doing one for me now.

I had Hill Country do my conversion and would tell you that I have no feeding issues with pointed spitzer type bullets, but do have some issues with the flat meplat bullets on occasion. May be something you address early in the building process if you wish to shoot those types of bullets.