Deegle
This is an area where more is not necessarily better! We started out many YEARS ago with 4 shot receiver mounts and NOW is see some that hold 8
. At bare minimum
4 in the gun and 4 on the gun ought to get it done. Don't get me wrong @ 3AM defending our castle in our skivvies extra rounds are NICE.
He is a 4 shot (SSGSS-4) that has been around for quite awhile and I can vouch works, and if you have to do anything besides bolt it on, PM me and I will yell at Wilson for you.
http://www.wilsoncombat.com/sa_side_saddle.asp
If you are going to use mixed rounds, remember to point your shot shells and slugs in diffenernt directions. That's the tacti
way!
WARNING;
one of the few things that can destroy a 870 receiver is allowing the hold down screws on this or any receiver mount to become loose and elongate the Trigger Plate Pin holes. Check the tightness frequently, or you will have a mean, old, ugly, Armorer like me yelling at ya!
I have experimented with butt cuffs, as long as they DO NOT move up the stock they are great. For a blast from the past, check out Milt Sparks Leather and look up COLD COMFORT, it's expensive but IT WORKS.
Good Luck & Be Safe