Looks and performs fantastic - Rival Arms RA20G512A Threaded Conversion Barrel Compatible With Glock 23 9mm Lug

You can’t go wrong with this rival arms barrel, it fits perfectly with no wiggle. Down sizing the ammo doesn’t affect the ability to eject but I wouldn’t recommend running a compensator without changing the recoil spring. With all the crazy things going on right now it turns out that 40 s&w is cheaper than 9mm at least in Washington state, so having the ability to simply swap my barrel is fantastic. You can also change out the ejection arm in the gun to get a better ejection pattern, buying the Glock 19 gen 5 ejector is the best choice just be aware that you may not be able to use the gen 5 trigger housing in a gen 4 or older but YouTube will guide you on how to disassemble it.