The average savage model 340 is currently valued at between 100-200 dollars depending on the condition of your firearm.
The value of a savage 340 BC 222 rem would actually depend on a couple different things. Some of these things would include the age and condition.
savage arms
Savage (Stevens) Model 340
Between 80-225 dollars,depending on overall condition and a good bore.
The savage model 340 series was made between the years 1950-1985.
1950
http://www.thegunrack.net/Magazines/centerfire_rifle_magazines.htm This is a Savage model 340, magazine in .222 caliber costs $24.95 plus shipping from this site.
You need a Weaver Side Mount #2 (which is the base). Weaver also make 1" side mount rings that mount onto this base. That's what I have on my .222 Savage 340.
The Savage model 340 was made from 1950-1985,while the Savage model 340C,and 340S deluxe were made from 1952-1960.Yours could also be made during this time span.
Without a serial number,I can only say that the savage model 340 was made from 1950-1985.If you would include the type of sights,barrel,barrel length,and stock design It would better help me in deciding with in which years your savage model 340 was produced.
50-275 USD or so
$100-$150