I posted a similar question on the uppers forum without much response. Thought I would try here next because of more traffic. I was thinking of buying some JP Enterprises tension take down pins for my ARs. I want to do this to prevent the eventual wear standard pins cause on the holes in the uppers that the pins go into. I have seen the pictures of the pins. Do the tension pins put tension without gouging or cutting into upper.I think the current take down pins are fast, but they eventually become loose as they wear on the holes in uppers. Maybe  some company should make the pins out a hard plastic that will be softer than the aluminum upper.

NO SLACK!

Since the tension pins are stainless steel, they are harder than the take down lug on the upper. The way the tension pin works is by using a set screw, as it is tightened, to cause the 2 pieces a cylinder cut in the middle at an angle to wedge apart.

I use one on a JP Enterprises built rifle. It really works well. I don't see how it could damage the upper/lower when used correctly.
The only complaint I have is if you have to open the rifle more than 3 times while at the range it becomes annoying. Of course this doesn't happen too often.
If you decide to use one its probably a good idea to buy a spare for the parts kit. I was able to pick up a second one real cheap as a spare.

Solution in search of a problem, IMHO.

A waste of good money.  

Has anyone actually worn out the hole in an upper?  

If so, was it properly lubricated or seriously abused?

If you are concerned about a tight fitting the upper and lower recievers, why don't you get an "accu-wedge?"  It is a little piece of red soft plastic that sits in behind the rear take-down pin.  It actually bears slightly against the rear upper reciever lug. It cost something like $5 at the local gunshows.

I learned something new today.  I didn't know that it is suppose to increase accuracy.

my groups in my HBAR were cut in half--Went from 1" to 1/2" from edge of bullet hole to far edge of other hole. if i had measured them like benchrest shooters do (Deducting bullet diameter) my group would would be sub 1/2". Havent used it enough to know about wear.  i did take an offset screwwdriver and an allen wrecn and put it the stock in case i forget to take my gun tools to range..Dick

OK...worst case scenario.  You fire your rifle so much that the holes you are worried about do get bigger.  So what.  If they get big enough to cause problems...and it's doubtful that will ever happen... then go for the JP pin.  Or, take your lower to a machinist who can drill the hole out large enough to fit in a bushing that will bring the lower back into spec.  I've had a 1969 427-435 Tri-carb Corvette since early 1970.  I worried about the engine wearing out all through the 70's and 80's.  I'm old enough now to understand that the engine is still doing just fine...but... as for me...I'm wearing out and at the rate I'm going...I'll need my own JP tensioning pin.  There ARE things that you SHOULD worry about, but this is DEFINITELY NOT ONE OF THEM!!!!