mgsgt's suggestion is a good one. Personally, I prefer to use JB Weld Kuick Set....not as strong as regular JB Weld, but for me easier to work with and doesn't run as much.
The Axis stock plastic design leaves a lot to be desired. You may be missing a problem with it and that is the overly large trigger guard part that also holds in the magazine. Please note how much of the wrist of the stock it occupies and its a thin wrist. Note how the rear of the trigger guard had a nub that sticks into the stock. Reads like you've dealt with flex problem from rear of action to front of the stock. However, from rear of trigger guard toward the butt of stock, you've done little. That wrist in the stock is very thin and trigger guard (which is part of the wrist area) has no good tight attachment to it and I think there is a definite flex in it. Chuckle, showed a new Axis owner at range with his rifle what I mean after he shot the rifle for the first time and had mentioned to me seems to be a flex to the stock. I rested the butt of his rifle on a shooting bench while holding the rifle just in front of the action. I then used the forefinger of my free hand and pushed down on the wrist area behind the action. Had him watch the joint of the rear of trigger guard with the stock. Chuckle, he noticed how the joint spread from my fore finger presure.....and I didn't exactly exert much pressure with my forefinger. I came to the conclusion about this problem after buying an Axis when it was called the Edge, several years ago. I own maybe 25 scoped rifles, most with a 24X or higher scope on them. The Axis was the first rifle I'd ever shot, that I could watch the elevation cross hair of scope climb up to a 1/2" on a 100 yd target while pulling its heavy trigger, while shooting from benchrest. I too, tried filling the cavities in stock, but never came up with a good solution to its flex in area where trigger guard joined the rifle.
Good Luck....I'm sure you are smarter than me. I solved the flex problem back then by cutting out the receiver portion of the Axis stock, flattening its sides and building a wood stock around it.