Mp7 Stock collapsing?

[Fung Li]

I have a KWA Mp7 and recently the stock has started to collapse on me while firing the weapon while shouldered.  The only exception to this is when the bottom tip of the stock is the only part resting on my shoulder, which is awkward and uncomfortable for me.  Any suggestions as to what is wrong?

[XavierMace]

That's pretty common with MP7's, not just the KWA. 

[bailey5671]

Never had that problem when I owned mine. Is the stock pretty used?

[Fung Li]

It's about 8 months old.

And I can hit the stock from behind pretty forcefully without it collapsing, it just decides to as soon as I pull the trigger.

[XavierMace]

It's not hitting it in that's the problem, it's hitting it vertically.

[Wolf Bane]

Got a picture? Might have worn down the locking plate or the spring isn't fully engaging into the locking position. Depending on what that joint looks like I could make some suggestions. If you're nearby I could take a look at it one weekend.