One ive used and have some success with, not loud but with practise i find it helps to get foxs in those last few yards
Take 2 spent shotgun cartridges and cut off the plastic, the melt/burn off the rest of the plastic
Pop the used primers from the inside out
Make a small slice down the side of one the brass pieces thats left
Now insert the uncut one into the cut one
Place some insulation tape around the circumfirance (spl)
Practise with it and you will end up with a low volume call
If using a mp3 then here are some calls
My link
