Harrington richardson arms

see if this link helps you out.
https://www.google.co.uk/webhp?sourceid=chrome-instant&rlz=1C1CHBD_en-GBGB719GB719&ion=1&espv=2&ie=UTF-8#q=Harrington+and+Richardson+single+shot+shotgun.+It+is+a+SD+%26+G+Special

Here is a link that answers all your questions. Sportster 8482 Sportster Compact Sportster 17 HMR

It should be stamped on the barrel. If not, please take it to a gunsmith. He should be able to tell you what lenght of shell can be safely fired from the gun.

stick with the manufacture

hmmmm not sure i could research it if you would like

Harrington Richardson went out of business, so the chance of finding out anything about your gun on the bicycle page is slim to none. I suggest you take your gun or the serial number to the local gun shop, he might have an answer for you

The Harrington & Richardson M4 survival rifle was made in the 1949 for the U.S.A.A.F. & U.S.A.F. It was meant as a survival tool for downed pilots and crews. 29,344 were produced. Depending on condition, they can range from $400 to $1,800. Also, be aware that the original military barrel length of 14 in. made this a short barreled rifle, which required a $200 tax stamp and paperwork from the BATFE. Most surplused to the civilian market were re-barreled to 16 in.

Before the gun control act of 1968, serial numbers weren't required by law.

Manufacturer of low end guns didn't bother numbering them.