6gns Unique. 7.62x39mm case. 220gn Sierra ProHunter. ~1000fps. When shooting outside at the range, it sounded like a .22short inside the clubhouse. 3.6gns gave me ~800fps. Couldn't hear it in the clubhouse if you were talking.
BTW, clubhouse wall was the back of the shooting line. Only a 4' aisle between the wall and the shooting benches. Can't remember what my loads were for the .303. But we were not going for silent, we were going for who could get the bullet sticking the furthest out of the barrel without it falling out.
I now would use 700X since it is what is on my bench if I were to work up any subsonic load.
H4831,
We too used to shoot in the basement and the back yard. No one minded. I used to walk through town with my shotgun (uncased!!) and pack to go rabbit and grouse hunting just outside the town limits.
We used to take our shotguns to school on the bus and keep them in our lockers all day just to get on another bus to go to a friend's house to hunt that night (the bus drivers insisted that we leave the firearms, in cases, on the seat directly behind them).
We even had the vice principal once ask us to see what we had brought and then we all went to his car, had a look at his shotgun, then he invited us out to his acreage that night to hunt. Now, I think that is frowned upon.