Wanted to share some knowledge as I had this issue trying to find a decent light bearing holster, specifically universal that fit well. The Tier1 MSP fits according to another post, but as shown it has a huge gap into the trigger guard, which I did not like. Unmodified, the gun fit, but was extremely tight due to the holster having barely not enough clearance for the top of the slide. With some breaking in it got easier, but definitely not something I would want to trust. Part of the holster also barely contacts the extractor, which is really not a big deal as I doubt it affects retention, but may scuff it which is a problem for some snobs. To fix both issues, I simply used a heat gun and two layers of painters tape. I then jostled the gun up and down to ensure plenty of extra clearance before it's fully indexed off the light. The extractor was clearanced by heating just the edge of the kydex, and pushing inward lower on the kydex, so that only the soft, heated edge will deform. If you do the same, make sure where you're pressing is sufficiently cool/set so that you don't put a nice thumb shaped indent in your holster. The only other place one may want to clearance is the sweat guard, which barely contacts the safety, but I imagine the flex from wearing or sitting with the holster is going to make it contact regardless of if you fit it. The only real "issue" some may have is the gap on the left/inside of the holster. It has a nice taper to allow reholstering to be easier, however because the rail adapter pushes the light a decent bit forward relative to most other factory railed handguns, the trigger guard sits further up in the holster, which I was able to pull the trigger in both DA and SA, but just, use your safety? I have pretty small fingers anyway, I have serious doubts anything would get in that gap, release the safety, and pull the trigger without you knowing. Couple more things of note with this particular holster as well. I bought the TCC clips, instead of using the included plastic monoblock. Where the square shaped nuts for the clip on the slide side of the holster sit is very close to the slide. If it were tightened down where one of the corners was facing toward the slide, or loosened up, I could potentially see the nut making contact with the slide. This wouldn't be an issue with the monoblock. Also, I took measurements of the 45 magazines, and they appear to be only 1mm shorts in one direction compared to a 45 Glock magazine, which Werkz makes a mag caddy for, but I didn't commit to buying that Incase the holster didn't fit the USP. Also, the mag caddy attaches using plastic rivets similar to automotive plastic clips for bumpers and trim, and I have no idea how far it may protrude into the holster. It may interfere with where the slide is in the holster. Also, the 9mm and .40 USPs slides are apparently 2mm shorter and an 1/8 inch thinner than the .45, either dimension of which I imagine would make the holster work without any fitting of the holster. The photos show in order the holstered gun after fitment, then both sides of the trigger guard, the right side being able to barely touch the trigger with my, again already dainty, pinkie, but not any other finger without pain from forcing, then the left side with the much larger gap, then where I applied the two layers of tape, the contact post minor fitting on the extractor, then the next two photos show the unmodified clearance contact areas. The extractor obviously sticks out further than shown when chambered as well. Last photo shows the holstered view of the left side unmodified, as I forgot to take a photo from that angle after I finished fitting. Also, the gun can pivot slightly up and down, though it's not the holsters fault, as I can see the light stays in place, it's the inherent play in the GG&G rail. It's nothing crazy either, I'm sure any other holster with that rail and light would do the same. Any questions feel free to ask.