I loaded it up in GRT just cause I was curious
Could not get to 13gn (pressures too low for GRT prediction model). 185gn bullet chosen.
24in bbl, 20gn H4895, 1560fps, 11350psi
16in bbl, 20gn H4895, 1356fps, 11350psi
FWIW, a bullet is accelerating at the muzzle. The pressure is not reduced to 'zero' force on the bullet unless you are using a very long barrel. Yes, people have tried that in order to get a no noise load without a suppressor.
I've shot a LOT of cast bullets from a .308. The mouse fart loads that work well are typically pistol powders. My favorite was 8gn of Blue Dot with 165gn bullets. I used this site to choose loads (their accuracy data was pretty consistent with my results as well):
Reloading Data for cast bullets, result of lever gun accuracy studies on cartridges: 357 Magnum, 41 Rem Mag, 44 S&W, 44 Russian, 44 Magnum, 444 Marlin, 45-70 Goverment, Pistol Powders, Large Capacity Rifle Cases
www.gmdr.com
The .30-30 data was pretty close to what I got in my .308.
Another consideration is that rifle powders are position sensitive at low load densities, ie, if you tip the barrel up before shooting the primer ignites the load in a more consistent manner. If tipped down there is a lot of free space that 'uses up' the primer energy and the powder may not ignite causing a squib load (yes, it has happened to me, more than once

). This is the reason most mouse fart loads are pistol powder. They ignite quickly and all at once no matter what you do with it.