The only subsonics that I've ever shot through my DUAxxxx series S&W M&P 15-22, blue springs & 2nd generation mags, are cartons of Aquila's 60gr SSS Sniper SubSonic 22 Long Rifle. No FTF or FTE. Other shooters locally have reported identical results with their older series of S&W M&P 15-22, blue springs, 2nd generation mags, and this ammo.
Two forum members here have reported that these 60gr rounds keyhole in their S&W M&P 15-22 rifles. They presume is because of the rifle's 1:15" or 1:16' barrel twists. I have NEVER experienced this, and neither has anyone else I shoot with, on paper targets out to 50 yards. Perhaps I'll waste a few rounds at a 100yd paper target next month to test for keyholes at that range.
We consistently have had one shot kills with these 60gr SubSonics, targeting the head or heart. They are noticeably quieter than your average 22 Long rifle ammo. Last weekend we discovered that they are quieter than the sound of heavy rain falling.