Quoted:
Hi all. I have an LMT Defender CQB MRP. California compliant.

The buffer retainer has bothered me, ever since I fit a Magpul ASAP and got to see the fit of the retainer. The retainer has a very "sloppy" fit in the hole bored for it. If I move the buffer in and out slightly, removing pressure on the buffer retainer and then coming back on it, the retainer moves back and forth quite noticeably. It rocks in it's bore. The special cutout on the buffer tube that provides a shoulder to hold down the retainer, is not covering it all that much. Just barely and there is no way to get another turn out of it without the lip being too far in.
Normal for the retainer to be held in place by a small amount of the edge of the receiver extension. Some folks turn the extension tube in further (too far) and need to drill a hole into the edge in order to allow the retainer to stick up and out, not a good idea.

I am afraid that with that much wiggle space, over time the hole in the aluminum will elongate and eventually allow the retainer to be pushed out by it's spring. Especially since there is not that much material on the buffer tube holding it in.
Normal to see movement in the buffer retainer. Very little chance of the hole becoming deformed and allowing the retainer to become dislodged.

When the buffer slams in and out under battery, does it actually contact the retainer every time? ie, Does it slam up against the little pin at the top of the retainer?
The retainer holds back the buffer only when you have opened the action. The retainer is not struck by the bolt group or buffer.

Or is there just enough pressure on the buffer from the BCG, once you close down the upper, that it keeps the buffer off the retainer?
Yes, that is how it is supposed to work.

So when it slams in and out under battery, the buffer just barely misses the retainer?
Yes, the buffer is in contact with the rear of the bolt group, and the retainer is no longer in contact with the moving parts.

I suppose I could have just asked......... does the buffer itself actually hit the pin at the top of the buffer retainer each time it cycles under battery, allowing for possible wear to the retainer and the hole/bore in the lower that it fits into?
If the retainer is being struck by the buffer, it will leave "chatter" marks on the face of the buffer.

Thanks.