G'day WCF and others.
I also took the plunge and added the 45-70 to the fold.

At the risk of starting a controversy. Now that we know the Baikal 45-70 is proofed to 33,000 psi,
there are some nice traditional loads that come in at considerably lower pressures. Have a look at the latest Lyman loading book at 45-110 for example. After seeing some of these loads I went further afield and got out my copy of GW's book to see what he had to say. Lo and behold the 450 x 3 1/4 NE in it's original cordite load went a little too high, but his loads quoted with modern components are going about 25,500psi giving a safety factor of 7,500psi! As there is little difference in the rim diameter the thrust factor should not be a problem.

Taking these figures into account and leaving overloading or the wrong powder being used out of the equation, (as this can be done with any rifle) could somebody explain to me why this type of conversion could not be carried out by a good qualified and competent gunsmith.

All the best and good shooting,

Ian.