mag extension

Plus 2.

To me, the answer would depend on the 870's mag tube length without the extension. I'd want the total magazine tube with extension to be about even with the barrel. Remington mixed things up recently with different non-extended mag-tube lengths.

Go 9 + 9



My own Rem 1100 magazine is about 1.5 inches past the end of my barrel.

It would just be a " personal preference " thing. At my club we shoot " pump gun Friday " out on SCs. Everyone bought [ or had ] a 870. We all bought from Brownells extensions so we could shoot 6 shots. Normally you can only load two shells, but here we made an exception because 6 birds were thrown on report. It's a lot of fun with many " short strokes " in the beginning. We got it down pretty good now. One guy even shoots a old Winchester hammer pump that holds a lot of shells.