The leak is usually due to the bolt stem vent hole being really close to the sealing edge of the oring. It won't cause any efficiency issues during normal operation. The oring vent hole being really close to the sealing edge of the oring can cause you to mistakenly use a carrier size that is too tight for your setup. This may cause the occasional bolt stick issue. When the bolt stem vent hole is really close to the sealing edge of the oring and no shims are installed, it is usually an indication that the sear is worn causing the bolt to sit farther forward than it normally would. I would check your sear for wear at the tip.
Except for the Automag in front, its usually the man behind the equipment that counts.