I'm glad you asked....The CIA had constructed shoulder fired assassination rifles which were equipped with silencers.
They used the 30 caliber carbine and re-barreled it to fire the 45 acp cartridge Thus they had a powerful short rang weapon that made no noise when fired. ( Those who fired the silenced carbine said that the only sound audible was the click of the bolt as it operated. There was a good write up on this carbine in a gun magazine many years ago....
Anyone can make stuff like that up. What is your source for the existence of such a rifle? And where can we find one?
.45 calibre is awfully big for a rifle - almost 2x the diameter of the 6.5 mm - 4x the cross-sectional area. Stability would be a huge problem unless the bullet length increases substantially. But that increases bullet mass and therefore the amount of energy required, so it needs proportionately more powder. But that is not all. Air resistance increases a the square of the diameter too, which increases the stability forces required. So spin rate has to be even higher to maintain accuracy. But to get a high spin rate it has to traverse the barrel faster. If you shorten the barrel you have to increase the speed even more. So I would be very surprised if anyone made such a rifle because it would have so many problems with accuracy.
