I thought this installation was going to be challenging but it was among the easiest of the upgrades I made to my Mossberg 500.
My 5/40 threaded bead came right out using a pair of pliers (be careful) and a test fit of the Tru-Dot revealed that, like other reviewers, I'd need to file the post down so it wouldn't protrude into the barrel. I did this in about 5 minutes using a hand file -- just go slow and do a few test fits as you go.
When it came time to align the sight, it naturally wanted to align with the dot facing the muzzle rather than the receiver; so I stopped 1/2 turn early and used a liberal dose of Uncle Mike's Loctite to hold the sight in place. I also dropped a bead of Loctite into the barrel so it would seep into the threaded hole from the other direction. Note, Uncle Mike's is a lot stronger/more durable than regular Loctite so this is recommended if you don't want to pull your hair out trying to align your sight. It hardens in 30 minutes but takes about a day to fully dry. I simply tweaked it slightly once the loctite started to harden and made sure it was aligned perfectly. End result, tritium front sight on my shotgun for about $40 and 20 minutes of install effort. Doesn't get much better/easier than that.
I took the shotgun out into the dark to try the dot and it's nice and bright. I've seen brighter but it's plenty bright for the application (home defense.) 5 stars!
Pros: Easy to install, works as described
Cons: Takes a little work to get it on the barrel
This review was written in the old system and had content requirements that are different than reviews written today.