Field Scout shouldn't increase the reserve ammo, it should increase the MAG size. The gun was designed around this particular perk but when the perk was changed to this, version the EXOTIC gun suffered. Just as the increased shooting speed becomes noticeable the bullets run out. Year 1, this wasn't a problem because Field scout was there.
Yes, faster reloading speed helps. Gauntlets, class perks do too, but reloading faster doesn't make the gun shoot faster as is intended.
In fact, take field scout off and put it on a hand cannon. Fix the mag size for Thunderlord so that this beast, works the way it was originally designed to function.