I have 2 shoulder holsters.
An Uncle Mikes and a Bianchi X-15
For some reason the hold down snaps will not stay snapped.
I want to carry a semi-auto in them but, don't want to buy new holster[s].
I am thinking LOC TITE.
Your ides are appreciated.

Check the inner part of the snap....there should be an allen head screw that worked itself loose, just tighten up and you should be good to go.

Well........to make it easy.

Take the Bianchi X-15 to a good leather shop and get new snaps put on. The DIY snaps are not good enough to trust holding a valuable firearm. I had to do this with a Miami Vice Classic but it had been in use about 20 yrs before I had to get new snaps on it.

Next, toss the Uncle Mikes to the curb. They are cheap to buy and not made to last. Spend a some money for a better grade holster. It will be more comfortable, last longer and look better.

That is a problem with snaps from time to time. I have now sworn off snaps and use Horsehide scabbards (Kramer Leather) with the retention built right into the holster and there are no snaps to fail.

You can squeeze the male part of the snap just a bit which will make it slightly oblong which in turn will tighten it up. You can also peen the male side with the face of a ball peen hammer while striking that hammer with another one. This will stretch the male part of the snap making for a tighter fit.

Or....you can get the snap replaced all together.

Chief38