Not recommended for glfa upper - Bushmaster .450 Bushmaster 5-Round Rifle Magazine

This is a well made and strong metal magazine. It said it is five rounds but I could only get (4) 450 Bushmaster rounds to work in this magazine. It will hold (5) rounds only if they are under 30 caliber which 450 Bushmaster are not. Also, I had problem with feeding in the GLFA 450 Bushmaster Upper from Optical Planet. I called GLFA and was told this magazine brand is known to cause the feeding problems in there uppers and was told to replace it was the best fix. May work well in Bushmaster Upper but not for a GLFA Upper.