I just re-barreled a couple of M77 Ruger rifles. A Green Mountain barrel blank was used and it had a 1/7 twist in it.
The purpose of these rifles were to use as heavy a bullet as possible at subsonic speeds and have an accurate rifle that was quiet, easy to reload using standard Hornet or .223 bullets and to out penetrate every other subsonic 22 made.
We have achieved those goals. The rifle is wonderfully accurate and rivals a subsonic .22 LR. It can be loaded down nice and quiet like or it can be loaded fast for the best of both worlds.
We started out using standard 55 grain .223 bullets. We had good accuracy and they were quiet...so quiet that the bullet slapping the paper was the predominate sound.
Then we moved up to the 62 grain bullets. Good accuracy and no issues.
The beauty of this rifle is that it can shoot the slick 69 grain bullets and put them in one hole. We started out with 2.6 grains of Red Dot and worked up to 2.8grains. Any more than that and they start going supersonic.
We put 5 shots in one hole and still its very quiet. We have a great load with the Red Dot and using CCI small rifle primers the loads are pretty consistent.
For an idea of what it sounds like, here is a video.
What do you think?