Apologies for thrashing, use "model" instead of "application".

COLLADA also uses "model".  Talked this over with
@shunter and @mramato

web.config

@@ -9,7 +9,7 @@
             <remove fileExtension=".gltf" />
             <mimeMap fileExtension=".gltf" mimeType="application/json" />
             <remove fileExtension=".bgltf" />
-            <mimeMap fileExtension=".bgltf" mimeType="application/vnd.gltf.binary" />
+            <mimeMap fileExtension=".bgltf" mimeType="model/vnd.gltf.binary" />
             <remove fileExtension=".json" />
             <mimeMap fileExtension=".json" mimeType="application/json" />
             <remove fileExtension=".geojson" />