Relieving Chamber Cones?

[Theodore LeDurt]

Is relieving chamber cones the same thing as lengthening the chamber? I have a 10ga with 2 5/8" chambers which will not allow a Gauge Mate (10ga to 12ga) insert fit in my gun. To alleviate the problem I'm considering lengthening out the chambers to 2 7/8", but saw in a book the term relieving chamber cones and was just wondering if this is the same thing?

Thanks for any help.