Can a gas leak affect bullet velocity?

[vicious_cb]

The amount of gas tapped by the gas port is insignificant in terms of affecting velocity. I believe it was Molon who progressively closed an adjustable gas block until gas flow was completely blocked and the difference in velocity between fully open and fully closed was easily within the SD in velocity for that ammo.

[ABNAK]

The amount of gas tapped by the gas port is insignificant in terms of affecting velocity. I believe it was Molon who progressively closed an adjustable gas block until gas flow was completely blocked and the difference in velocity between fully open and fully closed was easily within the SD in velocity for that ammo.

So considering the above, it sounds like the little gas leak was incidental (although complicating in trouble-shooting this issue) and that the issue lies with the Federal M855 ammunition. It's just that the way it presented itself was odd.

I can see the first two rounds in the mag being underpowered and short-stroking. The third had no more resistance being the last in the mag with nothing but the the follower underneath it, so it locked back (even if underpowered itself). But why were there no "one-sies"? Sometimes a 3 or 5 round mag of M855 would work fine, other times it did what I described.

That is the kind of luck I have with just about everything: nothing is clear-cut, always have to wade through dead-end sidetracks to get to the real issue. To be fair, this isn't 100% solved but it would appear that the ammunition is the culprit. That said, while I haven't shot a lot out of this 1K round bulk pack, I don't recall any issues before this with it. Maybe the gas port on this 12.5" Brownell's barrel is a little tighter and combined with an H2 buffer was enough to get finicky on me?