Need Info, on new m7

[jedimac]

Hello everyone I'm new to this forum, my question is I just purchased a new in sealed bag M7 bayonet by gen cut for my stag arms model 1 m4, but to my surprise the barrel is to long for the loop to reach the bird cage, i realized these were probably for the 20" rifles, is there any adapter to make it reach? I have seen some where a M7 that looks like it actually had another part of a M7 butt end attached to the end of it to make it longer to fit, any ideas or info would be very much appreciated. Thank You for your time everyone. Mike