>>532732
"Subsonic ammunition is ammunition designed to operate at speeds below the speed of sound, which at standard conditions is 343.2 m/s (1,126 ft/s)."
https://en.wikipedia.org/wiki/Subsonic_ammunition
"First was the Eley Subs Xtra Plus, which has a newer, lighter wax lubricant covering. The bullet weighs 40.2 grains of hollowpoint design. This is intended to give superior stopping power. Its actual weight was 40.61 grains and it produced a velocity of 1,032fps and 95.1ft/lb."
http://olegvolk.net/gallery/d/48825-2/eley_chipmunk_pistol_DSC5208.jpg
"Next I tested the Winchester subsonic hollowpoints, which weighed a measured 40.3 grains and gave a 1,065fps and 101.5ft/lb. There is a slight lubricant on the surface and the biggest hollowpoint cavity of all the bullets tested."
https://cdn.shopify.com/s/files/1/0211/0922/products/237a8cd42c53c481f2fa5861fde21a7933350aad_grande.jpeg?v=1440594210
"The Remington is a relative newcomer in the subsonic rankings, weighing in at 38.7 grains, and is almost a clone of the Eley, except it is shorter and it has three lubricant bands rather than two. The velocity and energy figures over the chronograph were 1,029fps and 91ft/lb."
https://media.midwayusa.com/productimages/880x660/Primary/383/383954.jpg
"The CCI ammunition has a measured 39.8 grains lead hollowpoint small cavity bullet, very different from the old hollowpoint copper washed bullet. The newer variety was fast for a subsonic at 1,077fps with 102.5ft/lb over the chronograph because it has a lighter bullet."
https://media.midwayusa.com/productimages/880x660/Primary/678/678232.jpg
"The slowest velocity ammunition tested was the 40.3-grain RWS bullet with an average velocity of 991fps and an energy figure of 87.9ft/lb. This had a very thick wax coating and nice hollowpoint design of relatively soft lead when compared with the other bullet types."
http://www.champchoice.com/IMAGES_PRODUCT/2132664_XL.JPG
"The Lapua bullet has a good pedigree from the target circuit and its subsonic .22LR shot a consistent 1,071fps with resulting 101.4ft/lb energy from the 39.8-grain bullet."
http://skietwinkel.co.za/wp-content/uploads/2014/11/lapua-subsonic-.22-l-r.jpg
http://www.shootinguk.co.uk/guns/ammunition/review-subsonic-22lr-ammunition-39882
>Remington Subsonic is one of those rounds that I referred to that's just barely subsonic, in-fact unless things have changed it will go supersonic out of a 24"+ barrel.
It seems to hover around the same industry standards as most. I suggested a long barrel to maximize the amount of force possible without breaking the sound barrier… the pressures will also help with cycling.
The American 180 Top Load Mag is spring assisted, so the round only has to provide energy to trip the catch, not advance the drum. If there are faults with this system, then there is an option to increase the spring tension, and fine tune your setup there.
https://www.youtube.com/watch?v=1-i5LeuvyiQ
Ultimately, I'm suggesting that you finesse the aspects of a rifle to a stable and plentiful subsonic round - horde that round - and meet your safety needs with a reliable purpose-built firearm.
http://www.whackit.co/play_whack_the_burglars.html
https://www.youtube.com/watch?v=-7rWeWymJDw&index=80&list=FL9QslYlhcStHoGyfVrILb0w