I'm a huge rifle enthusiast and not as well versed on shotguns. The popularity of deer rifles is shifting to smaller bores also. I've got a 10ga, 12ga and a 20ga. Hardly use the 20 ga much. I guess I use the 12 the most. I just wonder why the shift to smaller? I do like some of the smaller bore rifles. There's probably going to come a time in my old age when I would rather shoot a 20 than a 12. I'm already there with 30 cal rifles. I think I'm done with anything larger than a 7mm bore. But 10 years ago, it didn't make a bit of difference, I would be johnny on the spot to shoot a 300 win mag or 10 gauge for rounds on end.
I use an 870 also. Have used a 12ga for yrs but thinking about going to my 20ga with TSS but will likely use 7.5 shot. But won't make the change until I can spend some time patterning with different chokes...... all of this to save less than a pound carry weight???
It's a way to save weight for those of us getting older but who still hike 5 to 8 miles a day turkey hunting.
