AFAIK, all of the 500 models used the plastic trigger guard with the exception of the Military Spec Model 590A1.
That gun got the metal guard,, and it's aluminum not steel.
Things may have changed since I worked general repair in a shop. They are always making changes.
The trigger group/guard housings always had an issue with breaking and by that it was the two opposing small lugs at the front of the housing that fit into cuts milled in the frame.
We used to replace a lot of them.
I think many were broken by owners dissassembling the guns and pulling the guard assembly out they break the lugs off.
Other than that, the assembly is held in place by the cross pin.
There really isn't much that can pull the assembly out of the frame when the gun is assembled and destroy the lugs at the same time.
The replacement was just the same Factory assembly so there wasn't any thing stronger about it.
Some people 'smithed their own broken housings and repaired them with a steel strip across the front to engage the frame cuts. Good idea but getting the steel strip to glue securely into the plastic guard was the problem,,at least then. Maybe there's better glue for it now.
Then the Factory changed the design slightly sometime in the 80's and enlarged those lugs on the housing making them as big as the design would stand. Corresponding larger frame cuts to accept it of course.
Still plastic, these later larger reinforced lugged guards won't fit the earlier mfg guns with their smaller frame cuts.
Interestingly, the Aluminum guards are(were?) made the same way as the early mfg plastic guards are.
In that the Aluminum Alloy guards have the small lugs on them,,,not the larger reinforced updated 80's design of the plastic guards.
So an early mfg 500 that took the small lug trigger guard housing will accept the alloy trigger housing now.
But the new style alloy housing with it's larger lugs up front won't fit into the early guns frame cuts.
The plastic guards do use a small flat spring to hold the cross pin in position as a detent devise.
The aluminum guard uses a small ball & coil spring instead.
Both work OK though some say the flat spring can break.
I guess you can make that argument, but the end of the world may be this afternoon as well.
Mossberg 500 is a pretty good shotgun. Plenty of them out there.
The two extra bbls are at around $200 in value depending on configuration of course. But with that it puts the basic price of the shotgun with one bbl way down and a real buy IMO.
If you can't find 20ga shotgun shells in the Pittsb PA area,,then you're likely not looking very hard I would think.
A 20ga unloads it's pellets at the same vel (around 1200fps) as a 12, or a 16, or even a 410.
Great gauge.
