Pete, a friend of gun lab, Sent me some pictures of a rifle that has come into his shop for repair. When he tool it apart and check out all the components he notice the condition of the locking shoulder. In the following pictures you can see the damage that has occurred to the PTR-44 locking shoulder.
It is hard to determine if the position of the bolt was not properly lock it up. It looks to be to high. This could have been a problem with the parts as they were made, out of speck, or it could be a problem that has occurred over time and usage.
Pete ran a file over the locking shoulder and it did not scratch it, a sign that it is hard. It could be improper material and or heat treat of the material.
Just be warned and check out your own weapons to verify the condition.