Yup! As painter indicated it is a National Postal Meter/Union Switch and Signal carbine. Most likely date is late 43 to early 44. Around 50,000 of these receivers were received by NPM. Not rare, but somewhat less common. Barrel could be original. NPM did use a bunch of them. The RIA/EB stamp on the stock is an arsenal rebuild mark for Rock Island Armory. Nice looking post WWII rebuild!