A 7 Round tube does NOT always fit 7 rounds in the M4

For anyone else who couldn't find the answer to why a 7 round magazine tube on an M4, and probably the other products as well, couldn't fit 7 rounds - I could not understand why my new M4 LE model with a 7 round tube would not hold 7 rounds of my Federal 00 Buck or Slug rounds - I checked for a limiter (which there shouldn't be one as it is a LE model, or any other blockage or obvious cause. With a well-hidden reference on the internet about 2 3/4 inch shells being slightly different lengt

Thanks for all the great info in the this thread! I had trouble getting 7 rounds in my new Briley carbon fiber mag tube. I then added Briley's One Shot Extension before I decided to work on the spring. FYI the Briley spring that comes with their CF mag tube is 7" longer than the Benelli factory spring. Thanks to the info from @Birdog19 post I was able to shorten the magazine spring without a lot of trial and error. Shortened the spring to 16" sticking out of the magazine (with the One Shot