Which AS VAL should I use?

I have 2 AS VALs. 1 with an extended mag affix and other with the arrow bullet affix. Since the ultra mag is so OP I am not able to tell whether the arrow bullet actually does anything. It felt like it made a difference with 1 blackcape armor enemy by taking 1 – 2 less shots than normal. But I cannot tell the difference.

At the same time there have been situations where I needed to switch to a RAM7 to finish the kill due to lack of ammo. The extended mag affix AS VAL could have done the job better there.

Can anyone guide me with this? Can anyone tell me where the arrow bullet AS VAL will benwfot over extended mag one?