Harrington richardson 243 modle sb2 ultra would like to know the value of this gun

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

See Gun Manuals in For Gun Make Harrington Richardson eBay

AU series serial numbers were manufactured in 1980. Prices have gone up a little, but this is still a no frills shotgun. Excellent condition $175.00;, $125 to $150 for good condition.

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

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.

They went on to become NEF (New England Firearms)

The "TOPPER" line is still in production.

Modern day examples:

http://www.hr1871.com/Firearms/Shotguns/pardnerYouth.asp

http://www.walmart.com/ip/H-R-NEF-Pardner-410-Gauge-Shotgun/19415245


To give you an idea of value:

http://www.gunauction.com/search/displayitem.cfm?itemnum=7479120

http://www.gunauction.com/Search/DisplayItem.cfm?ItemNum=9602474

http://www.gunsamerica.com/941790457/H_R_TOPPER_410_GA_SINGLE_SHOT.htm

Firing pin is worn. It may make a slight dent in the primer, but not quite enough to press against the anvil inside of the primer, hence the misfiring

Talk to a gunsmith to see if he has any spares, or has the ability to repair the firing pin.