I have a springfield xd .40 . I was looking at the optics slide but says you have to convert it to a 9mm and they sell the set up with slide, optic cutouts, 9mm barrel and spring
Do i have to convert it or can i just put the slide on ?
I agree with @Mike164 I’d be leery of converting firearm calibers unless the firearm was designed for conversions or the manufacturer said the conversion was OK.
I have heard of people successfully swapping special made 9mm conversion barrels into Glock .40 cal slides. I don’t think the conversion works in the opposite direction though since the opening in the 9mm slide is likely too small for the .40 cal barrel.
Pretty sure that won’t work properly with your .40 cal barrel.
If you can’t find a .40 cal slide with mount option I believe there are companies out there that can machine your current slide to allow for red dot mounting. Just find a good company with a proven track record before you allow someone to make modifications. Especially if this is your self defense pistol.