I've had that problem building hard ball guns for the AK NG Pistol Teams.
Milliet made front sights with two rivit points and sold a Duel-Crimp instulation tool to crimp them in.
The way it works, you drill two holes in the slide, a v-cutting tool cuts a V on the underside of the slide, then the sight is crimped in. I'm never had a front sight come off with this method.
The tool here is kind of pricy if you have one gun. I am no longer in the Gun smith business, and WILL NOT take mail order buisness, but if one is close, and drops by with the sight and Millet Sight, I'll put in on at no charge. The Gooberment paid for my training and tools, you paid once (in your taxes) so I refuse to go into the commerical business.
You can also just remove the sight and replace it with one of the correct tenon size. My 70 Series Gold Cups have narrow tenons. I use the Brownell's staking tool.