I have seen many extensions for the Mossberg.
Here is a Maverick 88 Security 8-shot model that I picked up from Prairie Gun Traders (out of stock) a few months ago for $250. I added an ATI stock to it. No magazine extension required.
![]()
No you haven't.
You've seen extensions for the Mossberg 590 magazine tube. Not at all compatible with a 500/88.
This is what a Mossberg 500/88 barrel attachment looks like. You'll notice that there's no possible way to extend a magazine tube beyond it.
![]()



























