My understanding on the HK-93 is that the barrel twist was intended
for a lighter bullet than what is used in most 5.56 today.
I think a 55 grain originally ,and a 75 ? grain today.
If I remember correctly ,the original 93s had a 1 in 12 twist,
and later models a 1 in 9.
Some special ones were made in 1 in 7 .
Changing the bullet weight for the older designs could severely
effect your group size.
I'm not a 5.56 guy ,so I would ask someone more knowledgeable,
perhaps someone in the AR forums would know more about
barrel twist versus bullet weight for 5.56.
All I know about it ,is that someone I shot with had his groups more
than double in size when he used the newer heavier ammo in his 93,
and he said something about this.
I'm all about .308 .
1/12 twist ,145 grain to 175 grain.
I'm not real concerned with what velocity my round will topple at .
If I hit em ,they're worm food.