Buffer tube length - Aero Precision M5 .308 Enhanced Carbine Buffer Kit

I have installed this kit. They don't tell you that the buffer tube is 7 1/4 inch deep. The 1/4 inch is necessary. For an ar-10. And a slightly shorter buffer. If you do not have this length the bolt carrier will not catch back after the last round. Many tubes are represented as 15/10 They could be if they are 7 1/4". However ive got 3 of those in my parts box that will not work on a ar-10 upper.