Try running your fingernail over the areas in question. If you can just barely feel it grab, you've probably got anywhere from .002-.005 worth of material protruding into the throat. And I'd imagine that's enough to mess with your accuracy a bit, not to mention some possible leading problems.
Another way to check the throats is get a couple gage pins in .001 increments from about .005 under the throat diameter right up to the nominal size Ruger calls out. Checking mine with a dial caliper real quick I came up with .359. If you know a local machinist with a minus tolerance set of pins, he could check it in a few minutes. If you wanted to buy them and check it yourself they can be had from McMaster Carr (.com) for probably $3-4 each. But remember to get the minus tolerance, not the plus. That way when they fit, you know that your size is going to be the diameter of the pin, not a guess. They've got stones, too if you needed some.
I'd imagine Ruger's customer service could tell you what the spec is.