RE: Diaphram call help.
The flat part with the membrane faces forward. Put the call above your tongue with the raised part up. Towards your palette. Call should be forward in the mouth so that when it is sitting there, the end of your tongue touches the end of the membrane. Light puffs of air from your diaphram (not the mouth) should be used. Vary the tongue pressure on the "reed" to change pitch. Start with little or no tongue pressure and experiment by increasing and decreasing pressure.
Try not to swollow or gag. That's why I don't use a diaphram.
Looks like it is used for cow/calf sounds, so you may not get a satisfactory bugle with it.