[CAL]

Your RB has a ported barrel so its effective length is about 1.5 to 2 inches less that the quoted length

 

[CAL]

DOK, here is something that Tim Sundles of Buffalo Bore wrote on sixgunner msg  board and can be found in the FAQ/454 loads

The Cast Performance 360gr. GC and 27grs. of H110 will yield 1425fps out of my FA six in. revolver. This load is pleasant to shoot and is safe in the Ruger and Taurus. If you have a chronograph and an FA revolver, You can increase the powder charge SLOWLY, until this bullet is being pushed over 1600fps--only out of an FA revolver.

Your load data/RB perf data doesn't seem offbase.

-CAL

 

[CAL]

<!--QuoteBegin--></span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote </td></tr><tr><td id="QUOTE"><!--QuoteEBegin-->I checked several sites, including Magnaports, and there opinion is that the difference in velocity is negligible.  [/quote]

I may be mistakend but I belief the "porting" on the RB (been a while) is infact an expansion chmber with ports. That means you are still loosing approx 50-75fps per inch of porting . Simply, the gas is no longer pushing the bullet with meaningful force as soon as the bullet enters the chamber.

I don't see why the FA would be any stronger that the Taurus RB.  

This isn't a dig, but have you ever handled a FA?  I'll defer this to the guys that have done destructive testing but I believe  the gist of the story is to play by the rules with the non FA guns. There are guys shooting >300s at over 1800fps with the 4 3/4 inch barrels, I doubt you would want to run the 6inch that warm.

Then there are the  the tighter chambers of the FA ....

-CAL