Information is pretty well stated...
The Clipper is 305 based but has two springs instead of one, one for blade and one for scissors, BUT it looks like three because one is not a spring but a SS liner made to extend past the bolster and form the hole for the key chain ring. The springs are different thicknesses.
The 310 Whittler is 309 based and has always had three springs, just like the other three bladed stockmen would.
The 310 has NOT been discontinued, was first made in 1994 as a project with SMKW for sale only by them, later Buck continued sales in 1998 thru 2000 and now Bass Pro Shops offers it only by them, sold in the sliding wooden box. Some 310s may come with 309 stamped blades. There rarest 310 is the Limited Edition Brown Jigged Bone.
When Buck took over manuf. of the 301,303,309 and 305 in 1985, everyblade gets a personal spring. Two blades two springs. Three blades three spring. The other models that were made by Camillus sailed on with as they were pre-85 until discontinued.
Here is photo of 303s, Camillus and Buck.
Anyone who comes to my 300 seminar at the Smokey Mountain Knife Works meeting next week will receive a PHd on all of this........
300Bucks