That usually happens with carbon build up, you need to go to the tower and buy a barrel snake and that should clear the issue up. Just a little carbon cleaner and then a squirt of oil in the bolt you should be good to go. Oh and remember to close the dust cover while on mars, it gums up the gun.
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A small amount of graphite powder in the receiver should fix the auto but damned if I know what's up with the shotgun
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You forgot about a old earth company called Sentry Solutions. That should also be a part of every guardians kit. If it can be found in the ruins, it should be considered exotic.