Looking thru Magpul they apparently have 2 sizes available...I have no idea what to order, pls help, here's their note:
*NOTE: There are two basic sizes of M4 Carbine receiver extensions (buffer tubes): Mil-Spec and Commercial-Spec. If you have a Commercial-Spec extension on your rifle, make sure to order the Commercial-Spec CTR.
Specifications based on standard-length (flat-back) M4 Carbine receiver extension and may vary depending on tube manufacturer.
Friction lock performance may vary depending on the host receiver extension's dimensional tolerances.
*NOTE: There are two basic sizes of M4 Carbine receiver extensions (buffer tubes): Mil-Spec and Commercial-Spec. If you have a Commercial-Spec extension on your rifle, make sure to order the Commercial-Spec CTR.
Specifications based on standard-length (flat-back) M4 Carbine receiver extension and may vary depending on tube manufacturer.
Friction lock performance may vary depending on the host receiver extension's dimensional tolerances.
