Capturing on loopback device on Ubuntu LTS: 15 Mbit of traffic and "x dropped packets"

I am trying to capture about 15 Mbit of traffic on the loopback device on Ubuntu LTS using tcpdump, and I am seeing dropped packets.

The CPU is a freaking i7, and i have yet to see CPU usage go above 15% during the measurements i am trying to run. Load is negligible...

The capture is written to a file using -w.

I have tried the following (as suggested here: https://stackoverflow.com/a/7018039/55267 ):

• Set /proc/sys/net/core/netdev_max_backlog and /proc/sys/net/core/netdev_budget to arbitarily high values. No effect.
• -nn No effect
• Tried changing txqueuelen of lo. No effect.
• Tried using gulp. No effect.
  • gulp instructed me to:
    • echo 4194304 > /proc/sys/net/core/rmem_max
    • echo 4194304 > /proc/sys/net/core/rmem_default
    • No effect....

Is there something special about the loopback device in regard to lossless captures? How can I do a lossless capture on lo?