Let me add another perspective - almost all scope tubes are an aluminimum alloy. Steel and aluminimum expand at different rates.
The aluminimum rings are as strong if not stronger than their steel counterparts.
Go to Sinclair International and look at the scope rings available, most are aluminimum and these are used by some of the best shots in the world, yes mostly from benches, but on some pretty big boomers. US Optics has an interesting blurb on this very issue. Go to the following link, page 133 for their take.