I am sort of a glue head, always looking for the 'best' glue, for both knife work and woodwork. Several of the fancy and high dollar knife maker glues are good, they usually are named with numbers to make you feel like a Nasa engineer. But I have settled on three easy to get and cheaper glues. I like the super glue that comes purple and dries clear. Helps in seeing where it is put, especially when using just a little. Then I like loctite pro epoxy both 5 min and 60 min. The latter will bond stronger but naturally by its name takes longer in the "clamp". Both can be found in home stores.
Two part expoxies should be mixed well, I use a couple of post-it-notes and toothpicks. One layer of paper and it will bleed thru. I usually clean everything with alcohol and let dry. ON the shields I have reglued. (I will confess, I have robbed a sheild from a really beat up 300 and put on a really good missing a shield.) I take a small broken drill bit and CAREFULLY scratch the back of the shield. This gives the glue more surface area to grab on the metal. Its also best to CAREFULLY scrape any old glue off also, if it won't be a big chore. Then with NO extra amount of glue to leak out, replace shield. I usually use the super glue and use a tweezer to handle shield, after all 300 shields are small. For gosh sake put it on right side up.
Somewhere there is a thread where Joe tells what Buck uses to glue them but I didn't make a record and don't care to search......If I try to put some after market scales on a 300 I use the 60 min. epoxy and lots of rubber bands as clamps.
300Bucks