I am looking for some advice on what cold blue to use on some buggered side plate screws. The K22 is 85 years old and I want to try to come as close to a match as possible. I've look at the description of Oxpho and Dicopan but can't make a determination. Thank you.
Fred

I have used Brownells Oxpho Blue to touch up buggered screw heads with excellent results. The steel in screw heads seems to "take" the cold blue better than other parts of guns which probably have a different amount of carbon and/or nickel in the alloy. One tip is after the slot is cleaned up you want to match the level of polish of the screw head with the sideplate. For example, if you buff the screws to a mirror shine before applying the Oxpho Blue they will look out of place with the Service Style blue that S&W used post war up until the later 1950's. Or if you don't give them a high polish first, they will again look out of place on your K-22 which should have a pretty nice factory finish from that period.

I've used the Dicropan IM to blue rifle barrels. I expect that's more money than you want to spend for a couple screws. It's more than I want to spend to replace the almost empty bottle I've got.

Oxpho Blue works decently, and is probably your best bet. The T4 works on harder steels, like barrel bushings.

I've had pretty good luck with Oxpho blue and Formula 44/40 blue for touchups and small parts. I have found that cold blue works best on a bead blasted finish where it's appropriate, especially on front and rear sights.

Try em' both!

I have never used cold blue on a S&W. Have used a lot of it on
shotguns and rifles. 44/40 seems to get the job done for me.
Some guns won't take any kind of cold blue. If the Nickle
content in the steel is high, cold blue won't touch it. And some
of the cast steels won't cold blue. Seems like the cheaper the
gun the softer the steel, the better it cold blues.

Aside from the Brownell's Oxpho Paste and the 44/40 which are both very good, I favor the Birchwood-Casey Permablue paste. I stock all 3 because I find some work better than others on different guns, metal and parts. They are certainly affordable enough to get 'em all if you own a bunch of guns.