So if a slug gun, whether in 12 or 20 ga, is not a real elk gun and you say that what if you can't get under the 100 yd prescribed distance, what do you say about using a bow?
I have killed 7 elk with a bow and did not have one worry about whether or not I had enough to do the job.
The 20ga, with a rifled barrel and scoped, will shoot side by side, with any modern inline muzzleloader in todays standards, taking the time to find the most accurate slug combo possible.