Shooting a rifle with magazine touching the ground for support?

This practice will probably bite you in the butt sometime in the future. Most rifle magazines just are not designed to handle the shock of firing and supporting the rifle while in contact with a firm surface. Some rifles - like the M14 and it's civilian version the M1a - these were, but, they are more of an exception than the rule. I would expect the constant pushing up to wear out the mag anyplace where it comes in contact with the bolt - and then you would expect to maybe see more than usual bolt wear. If you would simply put a small mat, mitten, glove, or anything kinda soft under the mag it could save you from buying new mags a few years from now.

That said - supporting the rifle by the mag is not conducive to good accuracy. I could simply say, 'if it was a great idea, everyone would be doing it'.... but by balancing the gun on the mag you are not holding it tight enough into your shoulder. This practice can increase the felt recoil, very well could actually hurt and damage your shoulder over time - and kills accuracy.

This is what bipods are for. The stress on the mag at some point will cause a deformation that ends in a stoppage.

If it works for you then go ahead and do it. It isn't stoppages I'd worry about though, but accuracy. It's an unnecessary point of contact with the weapon and increases the chance of a missed shot.

A couple of points...never use your mag as a hand hold and don't use it as a rest. They are both great ways to get stoppages.....

Using the magazine as an improvised monopod is fine with certain firearms, such as the M16 and its clones, as it doesn't affect function in certain designs. In other firearm designs, it can lead to malfunctions and debris entering magazine wells. In the weapon you ask about, it's fine to do that.

if i caught you doing it in my section you would be peeling potatoes for months