300-MP powder and Hornady XTP?

I would use the Alliant data for all jacketed bullets of the same weight. Just start 10% below max and work your way up to your liking or to the max.

Yes, there has been problems of Lil Gun burning excessively hot and eroding forcing cones at max loadings. I don't know if the problem just pertains to the super magnum calibers or not.

As far as I know you can shoot a lifetime of 44 Magnums that are not over max pressures and still have a tight gun. Mine are.
When you load the two powders up you might want to see which holds the tightest groups too.........just a thought. Seems a lot of people now days are interested in power over accuracy for some reason.

Shrinkmd said:

I picked up a box of Hornady factory 240FTX, so when I reload 'em I can use same brass and bullet.

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You do know about the use of shorter cases when reloading the FTX bullets, right? Using these same cases for standard bullets and crimping in the cannelure will produce a shorter COL and higher pressures than most manuals give. This is why many folks use separate brass for them. This from Hornady.......

When loading FTX® bullets, it is important to keep in mind the longer
ogive of the FTX® bullet. This requires that the case be trimmed
approximately .020” shorter than when loading conventional bullets. This
maintains the correct Cartridge Overall Length, which is necessary to
ensure proper function in lever guns and revolvers.

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Your 629 will outlive you if you keep your loads within SAAMI limits. IMHO tho...... I wouldn't waste my monies on the FTX bullets for use in it. You will see no advantage in accuracy and velocity over standard XTPs outta your revolver and in most cases the terminal performance will not be as good.

The data for Hornady v.s. Speer is nearly equal with 296/H110 which are magnum powders of course. Though there is a very small variation in maximum powder charge (.6 for a 125 gr. bullet), this is probably more the case of Speer riding on the side of caution. Speer data often down loads slightly with exception to some of their new bullets, Deep Curl, that require a load range specific to the bullet. I load a lot of .357 mag. and 44 mag. using the Gold Dot and have never worked up any differently than as with a Hornady or any other bullet. Gold Dots are in fact a little softer than XTP's, but they are very tollerent to the higher working pressures created by magnum powders. Some regard the Gold Dot as a plated bullet which is kind of accurate. But because Speer uses a process that impregnates the core with a very thick outer plating, the bullet is as stable to load with magnum powders as is any jacketed bullet.
Let me know how that 300 MP works out for you. I've been interested in trying it, especially after eye balling the performance data.