For all who may be interested...
I sent my complete M&P10 upper to Black Hole Weaponry. I was looking for a 7mm-08 heavy barrel. Here is what we found:
The bolt and barrel extension are proprietary to S&W. BHW found that a DPMS BCG and extension will work in the S&W upper receiver.
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Do I understand this correctly, to change barrels all I need is a DPMS barrel and BCG?