Have you shot it or are you just assuming its too tight because it says "MOD" on the barrel? I use to think I needed more open chokes too but find most fixed chokes throw a better pattern and if you spend some time shooting and can get past the mental part of chokes I bet you will find MOD is really a good over all choke.
The pre 64 M-12's really pattern well. I have a 16 gauge 28 inch full I shoot skeet with all the time and though Im sure the full cost me a target from time to time I dont see it as a real problem.
So go shoot the hell out of that gun and if you give MOD a honest run I bet you find it perfect
Grouse/woodcock hunting here requires a very open choke as shots can be very close and fast. Pretty carry the shotgun at ready at times. I had a 20ga 870 for a while and switched it to a SK as the IC was found to be too tight.
