Many have said R5M. I'm considering it in the long version, since the long would have a larger shroud volume than the standard so it should be quieter at the expense of length and weight, but you also get more shots and better efficiency. I have 2 concerns with the R5M. The 1st is since it has an offset shroud adding a moderator isn't easy as buying something off the shelf. Therefore it has to be very quiet out of the box. jwilson has posted that by adding foam to the shroud makes it is real quite. Much quieter than my Marauder, I hope so because that's want I am looking for. The 2nd potential issue is that one owner is selling his because the hammer noise as too much for him. Ted in his latest Wildcat (Warcat) review has stated that all bullpups have too loud of a hammer strike for him except for FX guns. I have to take Ted's words with skepticism since I believe he is being sponsored by FX now and is probably biased to say the least. So any first hand knowledge of how loud hammer noise and muzzle report of the RM5 would be appreciated. Any RM5 owners in SF bay area willing to let me hear what is really sounds like would by very useful.
As for the Sniper HR and other semi-bull pups I believe all of them would need to add a LDC, making them longer and muzzle heavier not meeting my requirement of length, lightness and balance for off hand shooting
I think the Impact meets most of my requirements, but I believe that I won't be happy if it when it starts to leak. Nothing like putting the gun in the closet for a few weeks and then getting a raccoon raid only to find out that the gun has leaked all of its air. As said in many other area, it isn't if the Impact will leak, but when and how often.
I believe the R5M won't have any of the Impact issues, but is it quiet enough out of the box and how bad is the hammer noise.