I played around with different switches and managed to get an 18500 in a L2M without cutting any springs. I used a S1 tail cap and switched out the switch with a reverse clicky. The rubber boot is without recesse and placed into the tail cap with the switch sitting directly on top (no guides or spacers). Being a bit worried about switch compressing/shifting under pressure I placed an O-ring around the two exposed switch leads. The retaining ring with insulator is screwed on top. This gave me several extra millimeters clearance. I’m only 1 mm shy of completely closing without hard compression, that last 1 mm really increased the tension of screwing it shut, so I added a lanyard ring. So now I’m running a L2M with an 18500 under an Intl-outdoors 3 amp xml-u2 dropin with a Solarforce A001 head and a B6 bezel.