I acquired a 4 5/8" Ruger SSM as couple of months ago in a trade and have been working with both jacketed and cast bullets for it. However, I have been looking primarily at "Ruger only" level loads since I think the true potential of the little cartridge should be maximized. Most of those are based on Brian Pearce's articles in Handloader although there have been some great suggestions and posts on a thread I have in the reloading section. One notable recommendation for powder is AA No.7.
W/R/T throats, my revolvers throats are also tight. I cannot push either a Hornady or Sierra .312 jacketed bullet through the throats. However, that doesn't mean the gun won't shoot them! Quite the opposite in fact, since I have found that one of Pearce's loads using the 100gr XTP and AA No.9 delivers everything promised. It quite readily turns apples into applesauce at 50 yards. BTW, Pearce reports this load to give 1256fps out of his 6.5" gun, and having found his information to be very close to what I have obtained using his loads in the past, I do not doubt that this load is delivering as expected.
I have been casting bullets from the Lee 90gr tumble lube bullet mould. With my alloy they drop up to about .314, although I have heard of them going up to .315 with some alloys. Considering the chamber throats, I have been sizing them in a Lee .311 sizer with good results. They still hang up in the cylinder throats, but you can force them through. They have proven to be accurate with loads of AA#7. I am also working with higher end loads of WSF and HS-6 at the moment. The HS-6 loads are starting to look pretty good. I haven't chrono'd them yet, but the accuracy is there and they are most assuredly little "magnum" level loads. A combination of Lee Alox diluted with a few squirts of Hornady One-Shot is what I am using for lube. No leading. The alloy is lead:tin about 15:1 with a couple tablespoons of magnum birdshot thrown into the mix to add some antimony and arsenic hardening. They were a little too soft with just lead:tin and the magnum birdshot addition has hardened them up considerably for pushing faster.