Ok so this has been said a few times, hopefully with enough repetition it will be addressed and fixed...
When you have an item on that grants you the ability to carry more Heavy ammo it results in the loss of ammo when you die and go to orbit
Edit: also noticed the increased heavy ammo perk does nothing if you have field scout on your heavy weapon
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not only that but if you have 2 pieces of armor that have heavy ammo on them - thanks to a "fix" by bungie some time back - it no longer stacks.. which is bs. it seems they're all about limiting our use of heavies. -blam!-ers.