It was put out at a time when the DI 10.3-10.5" guns were over gassed by a bit and had issues running cans. The same isn't true overall today.
Without a can, the HK does eject more particulate/ fouling, but at a cost when looking at function. There's stresses/ strains/ deflections that come into play, there's also issue with some timing of events that don't help operation.
With a can, both systems unlock and open before the barrel pressure reduces to 1 bar absolute. That means fouling does blow back into the receiver. The time it takes to relieve reversion and release residual pressure (that contains fouling) is a longer event than the unlocking and opening by a fair portion.
I have experiance with the HK 416 series in various evolutions with the 10.x" and 14.5", including usage with AAC, Surefire, and KAC cans.
At this time, I don't see the need for this for most users.
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