Today Crosman air guns owns the Benjamin line of rifles and pistols. I suggest you contact Crosman directly and ask them.
See the link below.
I suggest that you go to the Crosman homepage ( they own Benjamin) and click on "Download a manual" there you will find the owners manual and parts diagram for your rifle. See related link.
Benjamin ( who is owned by Crosman air gun) recommends 10 pumps. Over pumping may damage the rifle. You can still get the owners manual for this rifle for free. Go to the Crosman link below and click on "Download a manual" at the bottom of the web page, then click on Benjamin and locate your rifle.
Crosman still has the parts manual for all it's rifles. On the home page click on "Download a Manual." Crosman owns Benjamin. see the link below
See the link below for the Owners Manual. It will tell you how to take care of the 347
Here is the link to all of the manuals for Sheridan and Benjamin. Crosman owns Sheridan and Benjamin See the link below.
The Benjamin or Sheridan pump rifle should never be pumped more than 8 times. See the link below for the owners manual (Crosman owns Benjamin and Sheridan air rifles)
The value of a benjamin sheridan 392pa 5.5mm 22cal air rifle is $185
Crosman owns both Sheridan and Benjamin. They have most of the manuals online. see the link below
See the link below for images of some Benjamin air rifles.
Crosman offers a free service to locate shops that repair Crosman, Benjamin and Sheridan older air guns. Crosman owns all three air gun companies. See the link below. See the link below for all the Benjamin manuals. I don't believe the 312 manual is still available.
In 1977 The Benjamin Rifle company purchased Sheridan air gun company. In 1992 Crosman purchased Benjamin. So now Crosman owns both Benjamin and Sheridan.
open the PDF (Owners Manual) when the page opens.https://support.crosman.com/hc/en-us/articles/203361124-340-Owner-s-Manual-1968-1986-