if your can shows up and 300blk is an option... especially out of a bolt or single shot (these will not cycle an AR)
get some .309 90gr xtp's (hornady #31000) and load them subsonic with trail boss. somewhere about 4.5 grains should be what you're looking for. bell the case mouth just a bit like if you were loading plated/powder coated lead. oal range 1.740-1.750".
its an XTP - so its got a stubby cylinder of a base and then just a short tapered nose to the HP. beauty is being an XTP - it opens up down to like 800 FPS . so at 1020fps mv.... its a very nice solid satisfying *thwap* when they hit something.
75 yds = 904 fps and 163 ft/lbs.
your 25yd rock wall = 975 FPS & 190 ft/lbs
zeroed at 68 yds - 1" high @ 25 yds, 1¼" high @ 50 yds, 1" low @75 yds.
big seller - its Hollywood quiet run suppressed.
i've got a half dozen giggle factor quiet subsonic loads for my CVA scout with trail boss. its my go-to powder if i want silly quiet. the 90 xtp is just one of them, and happens to be a great critter dispatcher for semi-urban environments or around livestock. the projectile performs excelent at the subsonic velocity range, and requires no modification to fire it out of a blackout (although if you want to, running them thru a .308 bullet sizing die wont hurt them and make seating just a smidge easier).
if you're not familiar with working with trailboss, they've got a handy document for load development thats crazy simple to use. so lots of options with a ton of calibers.
https://imrpowder.com/wp-content/uploads/2016/11/trail-boss-reduced-loads-r_p.pdf
hth