There are a lot of variables involved in actual muzzle velocity in both pistols and revolvers.
For example, I have a pair of PP's with 3.9" barrels and they demonstrate a 50 fps difference with the same load. That's mostly due to one of them having a slightly larger chamber and throat than the other (the difference between a new reamer versus an old reamer used in their manufacture).
With revolvers you have the same tooling issues, plus differences in cylinder gap on average between revolvers and even from chamber to chamber in a particular revolver.
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The .357 125 gr XTP is a very different bullet than the 125 gr FTX, and matching velocity isn't the most important criteria.
Hornady publishes a range of velocities for each of it's hollow point bullets where they will expand adequately without expanding excessively or prematurely. The XTP bullets were designed to expand at least 1.5x and demonstrate penetration between 12" and 18". In contrast, the FTX bullets were designed to expand pretty much no matter in heavy clothing tests, but they tend to over expand and under penetrate at the lower end of the velocity window. In my opinion, the FTX is a better choice, particularly if you keep it near the middle of its velocity range.
If you're using the XTP, you want to be sure that you use the right XTP and that the bullet is launched at a velocity that will promote expansion, which for the 125 gr XTP is between 850 fps and 1600 fps, while the 125 gr FP XTP is 1200 fps and 1700 fps.
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The popular internet wisdom is that the slow burning colloidal ball powders like Win 296 will produce maximum velocity in the .357 Magnum, but I've never found my chronograph data supporting that conclusion.
I have noted that 20 grains of 296 will generate a lot more recoil than 9 grains of Unique under a 125 gr XTP in a short barrel, but the Unique load will generate about 100 fps more velocity.
My preferred load is 8.5 gr of Unique. It's published data from the older Hornady 3rd edition, which uses a 125 gr Hornady hollow point, but a hollow point that pre-dates the current XTP, so take that with a grain of salt and use at your own risk.
I have used 9.0 gr of Unique but I noted that the cases start to stick in a Model 60, and I prefer my cases drop free on their own with a self defense load. The difference in average velocity in my Model 60 is 1,296 fps for 9.0 gr versus 1,252 fps for 8.5 gr, so in my opinion the extra 44 fps was not worth the extra pressure, particularly given that 1,250 fps is solidly in the middle of the 125 gr XTP's performance range.