As a teen in the 70s, I loaded a #0 buckshot (.320/49 grains) as a squib load in 8x57, and used a small piece of toilet paper to keep the powder close to the primer. I'd crimp the case slightly sans shot (not quite full stroke), and friction fit the shot in with a mallet tap because that was easy, and more importantly, didn't require me to change the crimp setting on the die. The load was apparently cool enough that it didn't fully ignite the paper, and some of it would flutter to the ground about 15' out the muzzle. I got the squib load and tissue idea from reading an article about squib loads for a .30-30, and extrapolated the load for the 8x57 based upon the case capacity they filled to in the .30-30 load (something like 10%). As I recall, it shot the paper pretty well at 25 yards with iron sights and was considerably quieter than a .22 LR. I kept a few in my pocket thinking they could be used on something smallish while hunting that didn't warrant a 196 grain bullet.

I'm thinking that a .45-70 subsonic load is still going to go *BOOM*.