I've been researching this too for over a month. The options are limited and really the info out there is "mis-leading". first if the gun doesn't have a pinned front sight you're talking $300-$500 at lease once you pay for the sight, send it to a smith, have the work done and pay for the right home. The D&L sights shown above are the best of the best with nothing close to them but you'll pay as much for them as a new revolver. It's over $500 to get them w/night sight inserts plush shipping.
HOWEVER, if you have an all stainless gun and you're going to keep it for life and then pass it down in the family and can afford it, you'll end up with a true treasure. In my opinion it would be a waste of money to do this with an Airweight because the refinishing options are VERY limited for the frame of the airweights since it's aluminum alloy combined with stainless steel components.
Have a 642; add laser grips or leave it alone and save your money.
If you have something with a pinned front sight then it's easier but I don't think ANYONE who's actually changed a front sight on a J frame will say it's EASY! It's a pain (or it can be) to get the pin out and no matter what sight you buy you often have to do some fitting and you can easily mess the sight up or the gun. Typically you have to drill the new sight and if you mess that up while trying to do it with the new sight clamped in the gun you can ding up your barrel if you're not real careful.
Search the web and you'll find a guy who posted doing it on a 640 with an XS big dot.
They do have XS big dots that fit a 640 but you won't find them on line where you can just buy them, you have to call them and even then there can be some minor fitting required.
There are a number of gunsmiths who can put one on for you and I've talked with several but the cost will be more than a set of LG405 laser grips. So it's a hard choice.
I just bought a 640-1 .357. I'm tempted to try installing a night sight myself which means buying the right sized punch, some new pins, the new sight and a new drill bit. I'm just paranoid though about messing up the gun! Still I think a single night sight up front would be perfect.
I've debated about the LARGE XS big dot or the standard sized XS night sight, or some other regular sized night sight. I think i'd like the normal size sight because it still gives me the night sight i want but the smaller dot will fit the channel a bit better than the larger XS and I want to be able to line it up a tad easier than the larger dot might allow but it's hard to tell since i've never shot the large dot.
I'm determined to find a way to do this as I don't really want to start using lasers on any of my guns.
If I could afford it, I would send my 640 to a gun smith for a complete action job, then get the D&L sights with tritium inserts and then have the entire gun re-finished with a fine bead blast finish and it would be my special revolver for life!!
Good luck on the path you take!
