system
Given the following post, respond as if you're commenting on Reddit:
human
Is a railgun chamber sealed up tight like a traditional firearm? If it is, does negative atmospheric pressure develop behind the projectile as it moves down the barrel? If it does, does it represent a problem or velocity limitation that has to be dealt with somehow? If so, how?
gpt
Railgun barrels are often sealed and pumped to vacuum in order to get rid of the shock wave that would normally be caused by the projectile moving at supersonic (in air) velocity.  The end barrier is just strong enough to withstand the vacuum, and is destroyed by the emerging projectile.