Guyon,
Buck used 440C until about 1981. Then, they started using 425m until about 1994. If the knife has a year mark on the tang and if it is from 1986 to 1994, the knife is definitely 425m. If there is no year mark, it could be 440C but is most likely 425m. Please check Buck's website for year marks.
Speaking of year marks, Buck currently has a twist on 110s being sold.
It seems they received an unexpected, very large order from a well known retailer and suddenly ran out of 110s. Because they had some 110 blades made up with the following stamp for 2002 (BUCK/ picture of small anvil / U.S.A.), they went ahead and made up a few 110s to get them through 2001 with the planned 2002 year mark. (The anvil replaces the planned symbol, a squared off U, for 2002.) At any rate, the 2002 110s will also have a 100 year medallion. That means that there are a few 110s in the pipeline with the 2002 anvil, no 110 number on the knife at all and no medallion. I have been ordering them for some of my collector friends now that the word has gotten out. Buck tells me there will probably be less than 1000 of these 110s made. If you want one, contact a dealer who is willing to order more 110s. As I stated, I have ordered several for collectors and they are just coming in this week.