My "bump in the night" Mossberg Shockwave "not a shotgun".....I even fashioned a rail mounted pointy-stabby for it.
I put a TLR-3 light/laser on top sighted for in house distance of 5-7 yards and it's the cat's ass. Very effective for in-house work for that type of "not a shotgun".
I also replaced the safety with a larger and much more positive metal butterfly safety.
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A word about Mossberg custom stuff. Pistol grip stocks are a no-no on a 590/500 due to the safety location.
There is simply no way you can manipulate the safety with your grip hand with a P-grip stock.
Now the Mossberg Maverick 88 guns are GTG in that regard as they use a cross-bolt safety much like the Win. 1200 Defender.