Had an upper in the shop this past weekend - piston upper (Osprey Defence) that had run flawlessly for a few thousand rounds. The rifle had started to short stroke and was FTE. Inspection revealed that the gas block had moved forward - it was an aluminum clamp on unit. I decided to remove the FH & the gas block to clean and inspect everything. I appears that the pounding from the piston assembly pushed the block forward to partially restrict the port - the hot gas combined with the port pressure to completely melt / erode the area around the port. There was no damage to the bbl.
The gas block is being replaced by a steel unit that will be either pinned or double set screwed into recesses in the bbl.
Pretty strong evidence that there is some serious pounding in effect when the bolt / carrier go back into battery.
On top of that - it also highlights the need for quality components - the aluminum gas block is clearly a low budget piece and I wonder what type of aluminum it is made from - definitely not a 6000 or 7000 series.
Pic attached below.
I’m not familiar with that exact setup, but the work required to cycle the system with parallel offset to barrel gas pistons instead of the inline with bore piston tends to be much higher than the system going into battery for either. I would examine the gas block movement from more of a point of perspective of initiating action movement from the firing moment more than the milder hammer effect of fully locking back again.
But again, I’m not familiar with that setup, and I hope it was NOT made that any of the components actually hammer the gas block/cylinder in any way.
