One more time;
The forcing cone is not the area of highest chamber pressure. Sure it is higher than further down the barrel, but the term "Chamber Pressure" sums it up. The Highest pressure is within the Chamber, not in the cone. "Unless" you cut that cone so Looong that its taper is less than the barrel's OD you have not weakened the barrel.
This is not the normal practise of cone lengthening, they are usually around 1˝" long.
Admittedly the cone Chuck mentioned in his .410 was much longer. I have seen virtually no .410's which had any concern as to wall thickness in this area. Well maybe one, a little 2" .410x.22L German combo hammer gun which as I recall weighed in @ 2˝lbs. Let's just say that anything at all which might improve the pattern of the little "67.49" gauge gun is worth trying. When you get to 28 gauge & upward it's not near so drastic.


Miller/TN
I Didn't Say Everything I Said, Yogi Berra