Tons of great advice here, my compliments to the posters.
I think that Thomas Edwards Lawrence said that a bayonet is a device likely to induce an injury to the person wielding it.
That said, they can be useful for guarding prisoners who might be inclined to grab a muzzle.
When it comes to 20 gauges and HD I am fortunate. Way BITD California was looking to buy 8,000 riot guns and Remington was in the bidding.
Trouble was, they needed to add an anti-jam feature to fill the bill. With only days left they turned to a gunsmith that used to be on their pro shooting team Don McClure (he was an ex cop too).
He came up with a cutaway on the bolt and that square U cut on the shell carrier that you see on the modern 870. They won the bid.
Don was an old friend. I visited him in California, and we shot together many times. He ended his days near here in Enoch , Utah at 93.
For years he worked on my guns. I brought him a Rem 870 in 20 ga and he added the anti-jam features of the big boy.
I tend to agree with Massage Aboob, .. uh excuse me,.. Massad Ayoob that no matter your size you can pump a second round out of a 20 ga faster than a 12 ga. Personally, at point blank range, I think that a 20 is sufficiently lethal to neutralize a threat.
The advantage of a 12 is that you can get, literally, hundreds of different kinds of loads. I have rounds made to start fires, control crowds, rubber buckshot and slugs for hazing bears, even anti drone bolos with hooks, and of course lead.
Whichever 12 or 20, I load one magnum 3" round and follow it up with 2 3/4" rounds so that the added kick lets you know when to reload.
If you train that way it could help.