All of the research I've done on this topic strongly suggests that it is ALWAYS illegal (ie, requires a tax stamp) to convert a rifle into a pistol. Specifically, if you buy an Encore rifle and then put a pistol barrel on it, you are
technically breaking the law. In a worst-case scenario, the BATFE Nazis will look at the serial number on the frame to determine how the action was sold and if it started life as a rifle, you can be prosecuted for making it into a pistol. In all practicality, this law has not been tested on the Encore, although there is a Federal court ruling on the Contender that is very clear. Some guys insist on buying JUST the Encore frame, or buying it configured as a pistol, then putting a rifle barrel on it. The key being that it started out as a pistol or just a frame. I don't think that is necessary, but it's my neck, if I'm wrong.
Long story, short? Don't cut up your bolt-action rifle: Save yourself the time and concern, while spending the same money to buy a pistol. (I'm imagining a 4-foot long belch of flame out of a 220 Swift pistol!

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