An easier fix and only costs about $2.85 Rockite which is a product used for repairing concrete and is harder can be mixed up so that it is a consistency of water. Now, I realize that the original poster had you cutting the ribs to add a steel rod. I will politely disagree with this method. The webbing that is on the bottom of the Axis is supporting not only the bottom of the stock but the sides. The trick to making it stronger is not by cutting it and then weakening it but by drilling holes through the webbing so that each of the cells are connected. Some engineer went through great pains to figure out how to make that stock rigid for the least amount of money. Take advantage of that, don't be quick to destroy it I also drilled holes in all of the openings around the lug. This is an area you do not want flex as well. I taped off the stock, mixed up my Rockite with water and stirred it well. I then poured the mixture into the cells until it was full. It hardens in about an hour.

When you remove the butt plate, you can fill the back end of the stock using the same method. There is a vent hole that leads to the grip area, a known weak spot on this rifle. As you pour in the Rockite you will see the bubbles come out of the grip and this will take out the flex and add weight. Once that area was filled I then added a paper towel wadded up. I then took two broken carbon arrows that I had and cut them to length to fill the rest of the void in the rear of the stock. I filled the area about 2/3s full, then added the arrows to the mix.

The stock is now about a 2 pounds heavier. It is as rigid, as I can not flex the stock in anyway no matter how I manipulate it.

The process is messy, the stuff runs out like water, which why it works so well, tape off the screw hole for the barrel bolt, and be prepared to wipe off the residue from the barre.

I had no idea if this was going to work when I tried. It is messy but works really, really well and cost less than three dollars and some broken arrows.