One alternative to using a compression sack is to stuff your jacket, assuming you carry a down or synthetic jacket, in with the sleeping bag. I have a WM Ultralite (very similar to the Swallow) and the regular stuff sack will accommodate a light down jacket without too much trouble, though it's tight. This works for me because I normally only use the down jacket in the mornings or evenings when I already have the bag unpacked.

I've read that a compression sack is capable of compressing the bag to the point of damage, which is obviously to be avoided with a $500 bag.
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Always remember that you are absolutely unique, just like everybody else. -Margaret Mead