Anyone seen this on back of Receiver?

[eb in oregon]

I expressed an opinion based on real life experience. You guys can go ahead and debate it to death, I've nothing more to offer.

[jond41403]

I expressed an opinion based on real life experience. You guys can go ahead and debate it to death, I've nothing more to offer.

Could it have been a defect like you said in your first post but they drilled it out before finishing? I'm not familiar at all with working with metal but if there was a crater or small void(small pocket) there that was not a uniform shape, could they have drilled it to create a perfect circle so no cracks would appear from the bolt slamming back repeatedly? I'm just wondering if they did that to prevent future cracking. I know the back is not an area prone to cracking but with a crater back there, I didn't know if it was a possibility. I'm not refuting your experience with metal at all, I know you definitely know what you're talking about, I'm just trying to learn.thanks