Did you clean it before you shot it for the first time? Clean out the chamber with a mop, rag, anything?
Depending on production, it may have been test fired and left to sit for awhile. Not sure I believe a dirty chamber from test fired, but you never know.
Maybe pick up another brand of ammo if able and see if it will chamber/shoot.
Also take the same bullets you have and cycle them all to check fit. When you do, cycle the same one in but rotate it slightly to see if it is fitting uniform.
If you reload and have 30 cal bullets. Take one of the fired cases and see if a bullet will slide in the neck. It should slide in without hardly any resistance. If it is tight and has resistance, the chamber is tight is the neck.