Great rule, since in the dark, it's hard to gauge what is in the back ground ,and with the slower round, it will cover less distance before it drops to the ground. Hence less likely to put a round into a farm house some distance past the game.





Again, understand why the rule in the first place, and with the bullet being pushed slower so it will drop to the ground with less distance covered, the HP rifle type bullet will lack the needed performance to put something down quickly (common problem with the 300blk at subsonic speeds as well).

Note, gravity is a constant, so if you shoot a bullet out straight/level, or just drop it from the same distance as the muzzle from your hand, both will reach the ground at the same time.  Its when the bullet is shot, that it is covering ground in distance, and the faster it is traveling in flight, the farther it will fly until it drops to the ground at the constant rate of gravity.

As for bullet designs, they produced to work best is a give velocity when they strike a target.  Hence a 308 round that is designed to penetrate and control expand, may not expand at a slower speed, and only punch a hole through the target like a Ice pick instead. Same can go for a varmit round that is designed to come apart on impact (which there are not meany in the 308 bullets), but even still, may not be moving faster enough on impact to exspand at all.

Easy to pull off with a Savage 212, brass hulls, and something like a lyman foster slug with mod'd mold (read 720 nitro express).
With the brass hulls, they can be fire formed and you can set jump to lands of the slug, instead of a lot of free run instead.
Just remember that as you are working up loads, to fiberwad under the slug once set to OAL, so the powder is packed tight in the brass hull tight against the primer.