I just put together a new AR using a RRA lower and a Bushy M4 upper. Everything fits great, except where the rear takedown pin fits. The piece on the upper that has the hole drilled in it to accept the takedown pin is extremely tight. I'm talking tight to the point on almost having to whack it with a mallet to get it in line with the hole on the lower. I cannot get it apart without banging on it either. It looks like the part that hangs down from the upper(not sure whats its called) is just a hair too wide as it is makeing some pretty serious rub marks on the lower.

I really hesitate to hit it with the dremel, but I cannot see another way to help loosen things up.

I've got another Bushy upper that fits perfect, so I'm not sure whats up.

Any advice would be helpful. Thanks.

You need to remove a small amount of metal from the hole on the upper. Put the dremel up and do it the old fasion way and use a file. You can always remove more metal but you can not add more back.

most likely your upper's rear lug has a burr or is oversized so...

completely remove the rear take down pin from the lower.  you will need to remove the stock. and insert the pin into the upper.   check to be sure the spring is good and there is only one detent in the hole.  two detents can cause this problem.  if that looks good you need to verify the hole in the upper is actually smaller than the take down pin.  oil the pin and slide it in.  it should go in easily with no play and no friction.  if not enlarge the hole as needed with emery cloth.    

the uppers rear lug and the lower should just touch each other and not drag or scrape when you put them together.  if they do dress the sides , front and back of the lug with a fine file.  make sure to keep the file square to the material.  

now check to see if the upper is sitting square on the lower.  if it's not square you need to file on the bottom of the lug to lower the back of the upper and make it so.

when you get the upper sitting square on the lower check to make sure the rear take down pin hole is lined up.  if not you will need to hog out (i love that term) the hole in the uppers rear lug.    


dremel's are good for a lot of things but with fine machining like they are not the best choice.

I just put a Bushy 16 upper on a Bushy lower.
The front hole was so tight I couldn't get it together. Took a piece of 600 grit rolled up and sanded until the pin fit. Re-installed the pin and now it's fine.
It sound like you need a little off the side.
If you don't have a fine file, you can do it with a sanding block with extra fine sandpaper.

Excellent advice guys. Thanks very much. Any particular size file or grit sandpaper I should use?

This is a common situation with RRA lowers. It is not really a problem and many people like the tight fit. I had the same thing happen with my RRA Upper on my RRA lower and many others have reported this 'issue'.

My recommendation:

1. Do not take a dremel to it.
2. Do not use sandpaper.

Continue to slap the upper into place. After a few assembly/disassemblies and a few hundred rounds, it will fit together nicely. The first few times, I had to use a wood dowel & mallet to remove the rear takedown pin, put now it works with firm finger pressure and the upper just takes a light slap to release it from the lower.

My RRA lower and Bushy upper where so tight, I "had" to do something.
I removed just enough from the lower to get them together. You should be able to see marks in the lower from the upper making contact. I have a buddy who took a little off the rear lug of the upper. Not much, just a hair at a time.