As usual Tim is right on! You mostly see a 3 ring setup on hard kicking handguns because of the ring "slip" associated with firing a heavy caliber with only the resistance offered by wrist and arm. Its not so much that the rings slip forward, but that the gun moves back against the mass of the scope without the shoulder to slow it down. With a rifle, except in extreme cases (see 375H&H) the butt stock tucked tightly to the shoulder against a 2 handed grip lessens the effect.
The only other major problem I see is that you may have trouble achieving the proper eye relief especially by using the extra ring on the receiver end.
Also, especially if your using aluminum rings or an aluminum scope tube, concentricity is very important to avoid placing the scope under stress possibly bending or denting the tube. Lapping should take care of that however.
JMH2¢
DG