I posted this question elsewhere, but nobody seemed to have any ideas...
I was out at an abandonment the other day and kept finding what appear to be strange shell casings. I know this spot was used by ETF (Toronto SWAT) for training purposes (breeching and hostage rescue). I do not know if these were left by them or not. They seem rather unconventional, as they 'extend' by about 10.5 mm. The casing is 9mm and if it held a bullet it would have been about 4mm - 5mm in diameter based on the opening. The only designation is on the primer and all it says is "E".
Has anyone seen these before or know what they are from?