I have yet to meet a M4ish AR stock that didn't have some wiggle in it. Granted, I have not played with them all but enough to see a trend.
Any wiggle reduces your ability to be consistent - the rifle simply will not recoil the same. Not a big deal in a 223 but not so good for a 308 and definitely not for a 338LM.
For min of bad guy, sure. But for bughole accuracy, it is a handicapp I would prefer not to have.
Why I prefer the design of the Chinese stock better. One piece, reinforced well at the root by the grip. SOLID.
Also, there are at least two attachment points from the grip to the stock. Will these loose with use? Is there flex here too?
An AR buttstock is hollow by design. Usually quite light. Is the rifle going to be overly nose heavy? Will ballasting the rear cause other issues by strainging the attachment points?
Is the detents for the stock adjustments going to wear and wiggle more when used? Are the stock adjustments going to survive the recoil forces (plastic on plastic mostly)?
I sense this to be a real world weakness because I have yet to see a 50BMG AR upper using a collaspsible stock. Everyone I see uses to the A1 solid stock.
If you wanted to mount that on this stock, you better be 6'8" or you will not be comfy reaching the trigger/bolt and the scope would be on an extension BACKWARDS.
Grip forward looks great though.
Jerry