I load bunches of 296 and H110 with 125's and just about everything else, and I've found that velocities are rarely ever consistent with the published data.
However, 21 grs. of 296 and a 125 gr. XTP runs about 1,500 fps from a 6" barrel, slower from my shorter one's. The max charge published is 22.0 grs. and isn't much different, if at all. I tried lighter charges, but 296 / H110 performs horrible when you take it down below published.
My recommendation is don't let the large published weights intimidate you, thus dropping the charge down significantly. This powder is designed to operate at the published data tables. I run published charges in my snubby K frames and have for a long time. And the problems with forcing cone damage is mostly rumor according to S&W, and has been extensively tested by them. According to S&W, it is often the result of leading in cone that pushes pressures up at the cone, not the use of 296 and 125 gr jacketed loads. I have a 66-2 and a 66-5 that have had countless jacketed 296 loads run through them, and the cones are is still in pristine condition. Good firm roll crimps, proper charge according to published data, and you'll be fine, in my opinion.
GS