No doubt the .44 special will kill deer, but why bother when you can use the mags? Simply a better tool for the job, especially past 50 yards or so. If legal, the specials would probably make dandy turkey loads, great varmint/small game rounds where noise is concerned, and less meat destruction. For deer, I'd say stick with the mags. Maybe if noise was an absolute factor, and deer are small, and range is very close, and if you can really pick your shot....
Just my opinion..
Mark