There are several reasons real functional suppressores ( not silencers ) are not used. Firstly and most importantly they are dangerous to use. Because their internal construction creates many pockets to catch unburned powder particles there is the possibility of a massive detonation. This could be after 6-7 rounds or 3-4 magazines worth of blanks. It WILL happen-it's only a matter of time. Secondly, yes they are 3-5 times the cost of building one out of alum. bar stock which a basically a "barrel extension" and does not attenuate sound or flash.
Movies are a visual medium and most directors want the look of the suppressor and the flash. I worked with Bay on BB2. He is brilliant and his movies make millions!! How else are most movie goers going to know if the gun is going off?? The uneducated public wants to "see" it!!
Re: BFA's ( military not movie blank adapted ) decible level being quieter than a real suppressed weapon that would NOT be true if SUBSONIC ammunition was used. Been there/done those comparisons with the decible meters. Military BFA's used with military blank ammunition produce approximately the same noise level as a movie blank 1/4 load. The blanks are extremely reliable but the flash has an orange/yellow color vs the white of a movie specific blank.
The most accurate depiction of a truely suppressed firearms is with "solid plug loads" These blanks produce enough pressure to cycle the gun but exibit no flash because of the totallly occluded barrel. The decible level is equivilent to a truly suppressed firearm with subsonic ammunition.
What is generally used is a 1/4 load blank. This gets you about 75 decibles with a small amount of flash, depending on the gun--more with a pistol--less with a something like an MP5. This seems to satisfy both the "artistic ones" and those most concerned with authentisity.
4570guy