EXPOSED: PEEK INSIDE 9 OF THE HOTTEST DRIVERS IN GOLF
https://mygolfspy.com/a-look-inside-9-drivers
Quite shocking to say the least. The hotmelt is being used to bring up the head weight to their required specs at the factories. The problem is obviously it could make each head slightly different - feel, balance, and sound. Knowing this, I would be afraid to order any non-weight-adjustable woods "online".
This also answers the question about why my (tour-issue) 2017 M1 460 head came with "lighter" weights than the retail model. The head (with the weights and the hosel adapter) weighs exactly 200.0g, which means it pretty much guarantees there is no hotmelt inside. Truly enlightening!
PS: I am now curious and want to open up my divorced retail R15 440 head, which never fully cooperated for the past 3 years... Forgiveness aside, any hits besides the bull's-eye dead center were complete garbage.