Last night I decided to do a simple cleaning of my Mossberg 590A1. This has the metal trigger housing and is relatively new with no replaced parts, everything is factory.
So far no issues and it has been a great shotgun. Cleanings have always been thorough and with breakfree CLP. I understand that this is a combat shotgun and not
a precision match rifle with a  6oz trigger.

All was going well until I got to the trigger group. I noticed the trigger seemed harder to pull than I remember and the trigger reset is sluggish.
In fact when I first pulled the trigger to get under the hammer it almost felt like the safety was on, when the hammer finally fell it startled me
because I didn't have my finger fully on the hammer to catch it. It wasn't a full dry fire but it was close.

Thinking that it might just be in my head I put it back together but the trigger had a gritty feel. The reset worked but if I held the trigger while
pumping (as if I wanted to slam fire it) the trigger would get stick in the pulled position. A light push forward and it resets. Also while manually
moving the hammer and trigger I notice the trigger pin is easy to remove and fell out several times. All other functions appears to be normal.

Google didn't help too much and I must have hit 50 sites looking for an answer with a variety of wording in the search, but not luck.

I take then out the housing and start to really look it over and notice that if I press the trigger housing takedown spring the trigger resets niceley.
This appears to be pressing into the safety connector and causing undue rubbing. when the trigger is stuck, a light press on the spring
lets everything fall into place. It could be unrelated but just an observation.

Next I took the trigger housing apart to inspect the parts. Everything looks good with no broken springs or other issues. The only thing that seems out of
place is the takedown pin spring rubbing on the safety connector. It would seem like a set screw should be there but the spring is too long for one to be there.
It all went back together with no issue but still had the same issues, a gritty and harder trigger pull with a sluggish trigger reset.

Now all this could be in my head and I just haven't looked at it in this much detail in a while but I'm having a hard time believing that. So that leaves something is broken
or out of place. Does all this sound normal or is something standing out as off? I would have pictures but I was up to 1am trying to figure it out and sleep was needed.

Thank you in advance, this one is really throwing me for a loop.

I had this happen to me almost exactly as you described it.  But I had one big difference, that being a TacStar Side-Saddle !!
I tightened the Side-Saddle's Trigger Thru-Bolt too much and caused binding on the receiver, making the Trigger Group completely inoperable.  Loosening the thru-bolt a little fixed the problem.
I didn't read in your write-up anything about a side-saddle, so this may not be the case with your shotgun.  If that's the situation then,  I hope someone else may have the answer you need.

This is all factory, I was cleaning it because the Magpul stuff comes in today.

So being factory, that eliminates that possibility.

So I called Mossberg today, It looks like that takedown spring is causing all the issues.

Since I bought this used, there is no warranty. A replacement is $65-75 plus shipping and
needs to go to a certified gunsmith. Brownells sells them for $92.99 plus shipping to my door.

That or I get creative with a tap and set screw for $10.

Has anyone ran in to this or have any suggestions?

Take it to your local smith. Odds are he can fix it on the cheap.

Hey I am a certified mossberg armorer and a gunsmith student at trinidad state. If you want shoot me a im ill get you my number.. I can probably help set you in the right direction.

They want $65-92.99 for a spring or a complete new trigger group??  Can you point out what part your talking bout in the schematic below?  Seems like you may be able to get a replacement part form them.

http://www.gunpartscorp.com/Manufacturers/Mossberg-33399/Shotguns-37443/500-41910/PartsList-34118.htm?page=8

The actual housing was bad. It looks like they press fit a bushing in to it to hold the spring back.
Something somewhere broke and allowed the spring to come out the back.

So the price I mentioned was for the entire trigger assembly.

I spoke the the gunsmith at Gander Mountain and showed it to him and he said the a set screw would work.

I also spoke with Platypus12 and he suggested a plastic housing due to it being very reliable.
(Thank you by the way, your advice gave me more trust in them in my next shotgun for hunting)

But in the end I decided to go the tap and set screw method.

With some math and measurements I got a 8-32 tap & drill set, tap holder and a 8-32 by 3/16in set screw
from Home Depot for $23.67. I figured I can reuse the tap & drill set and tap holder again so it gave me an
excuse to buy some tools.

I chucked the drill bit in a hand drill and slowly made the hole wider. Then I taped the hole. The set screw fit in fine.
Then the filing began, I knew the set screw would be too long to I filed it down to make it as short as possible.
Also filed it down from both ends to make sure it sits flush in the hole. Then I cut about 1/3 of the spring off.
After a few test fits and 2 more coils off the spring everything sat flush and the take down pin slides in easily
but still retaining the needed tension. A good de-greasing with hot water and simple green got it clean. Next I
assembled it all together and placed some lock-tight on the threads.

About an hour later I put the rest of the housing together and gave it a function test, Everything is working very
smooth, just as I remember it to be. The set screw looks good in there and if it ever works loose I will put epoxy
on the threads instead of lock-tight. It was a little nerve wracking but overall I'm glad I did it.

Thank you for everyone that helped. If anyone else ever needs to do this just shoot me a PM and I will
do what I can to help.