My Pedersoli SxS 12 gauge was made in 1978 and has the 18.3 stamped on the bottom of both barrels. From memory I believe the bores measure .71”/.70” at the muzzle. Pedersoli’s current spec says cylinder/modified, but remember mine being modified/improved cylinder. Believe the 18.3 is the metric equivalent of a 12 gauge. Modern 12 gauge bores run from .725” (Browning) to .730” (Remington and Winchester) if NRA publications are to be believed.Indeed, the bore is .720, as measured with a snap gauge. I can find no restriction in the barrels whatsoever. I measured from six inches down the bore to the muzzle. If I could figure out how, I would measure all the way to the breech plug. I will not attempt to remove a breech plug to measure it. I found this out, after I asked the question, so my apologies to the forum. Thanks to you Greymule, for your response.