I have explained it before so I will again. I have a couple CA Bulldogs and Taurus 431 as well as 3 L frame 44s and a I love 45s.
CA and Taurus both use a smaller ratchet. This allows them to move their chambers closer to the center and just fit 45 rounds. If you look at a S&W 44 L frame 5 shooter you will see that edge of the rim is right at the edge of the ratchet tooth on each chamber. Go in any at all and you would need to remove enough ratchet that it would not carry up. Plus they already had to reconfigure the barrel and frame to crowd in the barrel. LOOK at a 696 and you can see the barrel extension is really thin, and it isn't exactly thick on my models 69, 296 or 396 after they went with the 2 piece barrel.
So, in order to make even an L frame 45 S&W would have to go to a smaller ratchet diameter (more leverage needed to operate) which means moving the cut in the recoil shield for the hand, making everything in the action narrower so that they could move the hand over closer to center. Remember the hand works off the side of the trigger and must move past the side of the hammer. This makes the trigger to hammer engagements narrower also. You could make the off side of the frame thinner I guess, which would of course mean less support for the hammer trigger and other studs Then figure out how to lower the barrel in the frame. Bulldogs have a really tiny gas ring which helps. They also run a really thin hand.
Trust me I have measured the snot out of L frames, Bulldogs and Taurus guns trying to see if a 45 cases could be made to chamber in a S&W. Unless you move the chambers inward, reconfigure the barrel, ratchet and hand you end up with paper thin outside walls on the cylinder.
I don't think S&W is going to redesign their frames and actions just make a 45 that holds one less round and is just a bit smaller than a N frame for a few thousand sales.
I have a 325 PD and a NG, both hold 6 rounds of 45 acp are far lighter than my model 60 and hey with the Ti cylinder as light as a 5 shot bulldog.
