I have a gen 4 glock 19. I have seen that you can buy a complete .40 cal slide and put it on the frame and it will work, the only thing being that it has a little space in the front. My question is that some people say that you need to change out the trigger housing to a .40 cal instead of having the 9mm one. https://www.lonewolfdist.com/Detail.aspx?PROD=123269&CAT=200
While others are saying that using the same frame with no changes is 100% fine. Does anyone have a experience with this?

The reason, 'Why' the THU should be changed is because 9mm & 40 Cal. Glocks use different ejector configurations.  As far as I'm concerned you're playing with a, 'crap shoot'.  The magazine followers are, also, different.  If you're going to go as far as changing out the entire slide (Which with a 9mm you ARE going to have to do.) then the only things left are the ejectors and the magazines.  Personally I wouldn't do any of this; but, then again, I carry my Glocks; and it's taken me, literally, years to make them into the utterly reliable plastic pistols they are today.

Where are you going to buy the complete 40 cal slide, barrel, and spring?  What is the total price going to be?

i already bought a complete upper slide for 200$ shipped

The only differences in the lower half of the 9mm and .40 Glocks are the ejector...







...and they're not THAT much different.



There some differences in the slide components, but if you have a COMPLETE 9mm slide and a COMPLETE .40 slide, you don't have to worry about any of those.

yes i have a complete 9mm slide and a complete .40 cal slide