The .45 IS VERY Difficult to Suppress
Everyone. I own several suppressors, and I own a .45ACP Can. The .45ACP round cannot be adequately suppressed. Matter of fact there is NOT ONE hearing safe suppressor on the modern day market today. Every .45 can out there to be shot from a pistol to be hearing safe has to be fired wet... I.E. A small amount of artificial environment introduced into the rear of the suppressor.
The reason why?
The .45 is a HUGE round. The hole in the end of the can is several thousands of an inch larger than the bullets OD (outside diameter). For suppressors to be effective the gases have to be contained in the can. The hole in the front of the .45 can is too large to facilitate effective gas retainment. Therefore the sound cannot be adequately controlled. REGARDLESS OF HOW INHERENTLY SUBSONIC THE ROUND MAY BE.
Contrary to oldcspsarge's post, the Glock & USP Tactical or the MK23 firearms as well as the 1911 series all have the same sound signature to them. Your ears will ring from the report of the .45 round. Actually .45 and 9mm shot dry sound a LOT alike. When you shoot a .45 CAN wet it is enjoyable, but you can only get 10 or 15 shots (depending on suppressor model) before the sound becomes almost intolerable. He is correct that there is more breach blast from the 1911 platform (typically) than what you have with the 'cam' designed barrel lock up (the Glock & H&K series), but all platforms, shooting the .45 dry and without ears is unpleasant to say the least. ANYONE who states otherwise does NOT own, or has not shot a .45 suppressed before.
I have a submachine gun chambered in .45 ACP. When I shoot single shot its loud enough to make my ears ring. When its full auto you can hear the sound diminish as the gas builds up inside the can. Granted it doesn't drop by much, but the sound change is noticeable. GRANTED my MAC 10 is an open bolt gun and the sound of the bolt falling is quite loud in and of itself, but it wont cause your ears to ring. The suppressed MAC 10/45 SMG will (slightly).