IIRC that's a bolt catch cutoff.

Train of thought: If you are in the desert and your gun runs empty the bolt closes and no dirt/sand gets blown into the gun.

If you want to administratively hold open the bolt simply deactivate the feature.

The G3 didn't have a bolt hold open, the Brits deactivated theirs on the SLR/L1A1 although it was initially present.
IIRC on the G36 the bolt hold open could be deactivated as well, but I've never seen it done at the Bundeswehr.

 

IIRC that's a bolt catch cutoff.

Now there are six million and one ways to die.

 

Ah, there it is (EP3591329A1).

My memory didn't trick me:

The invention relates to a breech catch device (36, 36 ') of a self-loading firearm (1, 1') comprising: a breech catch lever (39, 39 ') adjustable between a release position and catch / hold position, and a blocking device adjustable between a rest position and a blocking position ( 42, 42 ') for optionally fixing the locking catch lever (39, 39') in its release position, characterized in that the locking device (42, 42 ') is in its rest position out of engagement with the locking catch lever (39, 39') and in its The locked position is in engagement with the locking catch lever (39, 39 ') and deactivated.

Nachteilig können über diese Öffnung des Auswurffensters insbesondere unter widrigen Bedingungen,Verunreinigungen, wie etwa Sand oder Schlamm, beispielsweise in Wüstenregionen durch aufgewirbeltenSand, in das Innere des Waffengehäuses und deren Bestandteile hineingelangen, und darüber zu Funktionsstörungen der Feuerwaffe führen.

The disadvantage of this opening in the ejection port, particularly under adverse conditions, is that debris, such as sand or mud, for example in desert regions caused by sand thrown up, can get into the interior of the weapon housing and its components and lead to malfunctions in the firearm.

In früheren Zeiten wurde daher zum Teil gänzlich auf eine Verschlussfangvorrichtung verzichtet, umso die Waffe universeller verwendbar zu gestalten und die Funktionssicherheit zu erhöhen

In earlier times, therefore, a bolt catch device was sometimes completely dispensed with in order to make the weapon more universally usable and to increase functional reliability

 

If am in a firefight in a sandy environment and actively engaging the enemy, my desire to know I had expended my last round would be greater than my desire to reduce the possibility of sand getting in my weapon.

This makes no sense, operationally.

The G3 didn't have a bolt catch for mechanical reasons, not tactical reasons.

 

If you say so.

 

I mean...If I don't cant the rifle to see the bolt's locked to the rear only to wing out the empty mag when I rotate the gun 180 degrees on its axis...Costa style...then what kinda fightin' is this???

(Note: heavy sarcasm)