I took my AR556 (SR556 upper on an AR556 lower) to the range today and ran into a problem I've never seen before. About mid magazine the bolt carrier locked back but not on the bolt catch. It was stuck fully into the buffer tube as far as it could go. It finally let loose and closed after using an empty case to lever the actual bolt head forward. When I took it apart it looked normal except for marks on the back of what would be the gas key. There were matching gouge marks on the charging handle. While it was apart I pushed the bolt carrier into the buffer tube like it was cycling and the buffer never bottomed out, the gas key was able to hit the end of the buffer tube. I tried the same thing with a second bolt carrier and the same thing happened. Both BCG and buffers will bottom out in the SR556 lower and buffer tube. I then took the butt stock from it and the SR556 lower I also have off and compared the two. The AR556 buffer tube is actually an inch longer but has the identical buffer as the SR556. What caused the jam was the back of the gas key slamming into the charging handle and wedging its self there! Is this a known issue with these rifles or did I just get a Friday rifle??