Hello Darat100 and welcome to the show.
To respond to your post...
I've fired 2-3 boxes of factory loaded .357 Magnum ammunition through my Handi. The groups would not be benchrest winners, but would certainly suffice for deer. At 50 yards they were consistently under 1.5 inches, while at 100 yards they would be 2-3 inches and showed about 6-8 inches of drop from the zero at 50 yards.
There's not much bother to recoil-sensitive shooters. I have no idea what velocity the bullets were, but I did disassemble 5 of the factory loaded rounds to weigh the powder charge. They were all at 16gr. and as they were Winchester loads, I'm going to assume that they were loaded with Winchester 296 powder. My link to their site is not working, but you could easily obtain the spec velocity from there.
For buying rounds, stick with the heavier bullet offerings, the light ones won't offer much gain in a longer barrel and may actually be slower than they would be in a 6" bbl.
Hope this helps,