Looks like poor workmanship when they were making that barrel and cleaning up the brazing when they attached the mag clamp.
If you contact them about it, they'll likely replace that barrel.
Send photos to customer service, they'll probably want you to ship the whole gun back to them, but I would not, unless they were flipping the bill for the shipping. You will need to include the guns serial number with barrel.
But, contact mberg customer service and see what they say.