[John Sabato]

I see what you mean by the lack of a barrel flange. This could be a problem, but only time can tell... The receiver was designed to have a full flange, but can function with a limited flange provided the barrel is torqued adequately. What is adequate? With a full flange, usually 1/8th turn is usually about right. With a reduced flange? who knows.

My recommendation would be the same as Jerry...make sure the headspace is correct. Then make sure you have a witness mark so you can periodically check it for movement.

The way such a barrel as shown happens is that the person doing the conversion chooses a rifle barrel that doesn't have sufficient diameter in the chamber area to provide a flange. It may be that the person who did this conversion didn't have more than one barrel to choose from...