The 305-gr WFN GC load will chamber in the 29 - 629's as I still have some of those very same bullets loaded up on my brass. BUT, I will not be shooting these heavy loads out of my 629 as they are not as strong as Rugers period. If you get into reloading you can shoot these at a moderate fps say around 1200 and still take down the wildest beast north america has to offer.
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My loads for the Ruger were pushing 1288 fps out of a 4 5/8ths barrel, but I'm not going to push this out of a S&W 629 6" barrel, you really don't need to.
Here is a link to:
http://www.buffalobore.com/ammunition/default.htmCheck the ammo selection for the .44 Magnum...
340 gr. LBT-LFN GC . (1478 fps / M.E. 1649 ft. lbs.)
NEW HEAVY 44 MAGNUM +P+
This new load is designed for only certain revolvers that have the cylinder length to handle it. They are as follows. Ruger Red Hawk, Ruger Super Red Hawk, Ruger Super Blackhawk or Vaquero, Freedom Arms Model 83, Taurus Raging Bull and Dan Wesson Revolvers. Suitable rifles include T/C Encore, "modified" Marlin 1894, Winchester 1894, any rifle with a falling block action and the Handi Rifle.
I really doubt if you will be able to chamber these in a 29/629.