Every time I behead a foolish loyalist space marine with my chainaxe (and after calming my berserker rage) I wonder " Is there a better method to do this kind of stuff ? ".
Indeed, the World Eater's method is very simple. But what about the other legions?

Tell me what is your way to do this.
All means are good to kill theese damn loyalists !

World Eaters actually have different ways of execution...

But anyways, if I were to execute a victim I would rip out both his hearts, and finally his spine.
And probably eat his eyeballs, because they're nutritious

Or you could strangle him to death with a chain like I did during the shadow crusade.

Taint them into coming to your side.

Two bolter shots to each kneecap, followed by two to the arms to disable them from fighting back. To show that they are inferior, kick them in the chest and place one boot on them. Finally, kneel down and slit their throat, and make it messy so they can't heal fast enough.

Shatter their faith in the dead-father, shatter their faith in the brothers who they hold a bond, shatter their defences, shatter their will, shatter their loyalty. If they see truth and join the your warband, shatter any doubt they have in your leadership.

If they fail to see reason... Shatter their legs, shatter their arms, shatter their hope and crush their skull.

Blood-Blood is forever.

You whelp of a chaos lord! The only good loyalist is a dead one!
Id rip off every limb and tear out their eyelids so they can watch me slowly disembowel them!!
Have them witness their slow demise rather than corrupt the sorry blind fool!

Then our armies would number few in numbers, our ranks most be filled one way or the other.

Well of course you'll have to worry about the number of marines you have, your black legion.
Your army is practically worthless i'm surprised you guys still tolerate abaddon's leadership.

*Pulls the plug, and shuts the doors to the catacombs.*

That is the end of that.