Vented Gas Block Modification for the 10.4 inch Hk MR556
The vast majority of 10.4″ Hk 416s made don’t have the gas port on the front of the block
that the longer barreled 416s and MR556s have.
For the standard 10.4″ gas block modification we weld the MR gas
block closed and then polish the weld down, so that section looks and works
the same as the 416 block. The 416 block does have a couple sling loops and
bayonet lug mount that the MR block doesn’t have, but those obviously aren’t
necessary for function.
A very small number of 10.4 416s had a vented gas block, with basically a
smaller gas port in the block. I can replicate that modification as well,
the cost for that mod is $195. With this modification we machine out the original gas port, weld in a new smaller port, and finish it down so it looks similar to the standard vented gas block.
The reason for the vented gas block is some guys feel that the completely closed
off block has a little bit too much recoil when used with a suppressor. The
vented gas block does moderate the recoil both with and without a suppressor
installed and makes for a noticeably smoother operation.