I have installed Trijicon HD sights on all my SIG pistols except the Legions. I noticed the front sight on my P220 Legion had worked loose and tried several things to get it to stay put but it keeps working loose under recoil. I decided to replace the sights with new HD's for my old eyes and installed them as usual with my SIG sight tool. The dovetail had a tight fit. When I ordered the sights I found that Trijicon makes a special model for .40 and .45, apparently more recoil resistant. I went out to my range to run a 40 round course of fire with the new sights, which went great until the last 6 rounds at the 15 yard line, where the new front sight fell out and was lost. I came in and called Trijicon Customer Service and told them what happened, and they are sending me a new front sight, so kudos on them. Looking at the fact that they offer a front sight for .40 and .45 caliber guns I am thinking front sights coming loose must have been a common problem.

When you re-install the sight use Loctite 620 (small gap tolerances). I use it on all of mine. Dave Dawson has recommended for years on all of his sight installations. There is a You-tube of his method.

The only thing different about the .40/.45 front sights is they are taller than a 9mm.
Generally a #6 front and a #8 rear.
Sig sights are 0.230" tall for #6 and 0.220" tall for a #8 front.

I don't go by caliber for sights but what's on the gun to start with.
My 220 came with #8 front and rear.

Loctite 620 will keep it from moving as suggested.

I got a replacement from Trijicon and the base of the sight is definitely thicker than any of the ones I have installed on 9mm. It has to be fitted to the dovetail. All is good now.