For grounding barrel crimps you need to consider what brand you are crimping. Buchannon specifies a 4 point crimping device be used with the barrels they produce. T+B specifies a few two point crimpers for the barrel crimp tubes they produce. I use the T+B brand. I am seasoned enough to remember when we did not always have to use a mechanical on the end of the twisted together grounds, and properly twisted they stayed together nice and tight. That is the reason I do not worry so much about using greenies like some here who only have experience since the great ground termination debacle code change came along....
If you feel that you cannot properly twist some conductors together for a few inches and keep it tight, use the greenies, they are fool proof.