The RE-10/A5SR receiver extension tube is designed to work with the Vltor A5 Rifle Recoil System, and can also be used as a replacement receiver extension tube for the AR-10 Rifle. It is important that you understand the requirements for the additional components, based on the intended application.
Physically, the A5SR tube is slightly longer than a traditional AR-15 receiver extension tube and is functionally the same length as the AR-10 receiver extension tube. The A5SR tube has six locking positions and is designed to work with a MilSpec, collapsible stock, such as the Vltor Improved Modstock.
If you are using the A5SR tube as part of the Vltor A5 Recoil System on an AR-15 type rifle or carbine, it must be used in conjunction with a Vltor A5 Buffer & Spring. These parts are NOT the same as standard carbine or rifle receiver extensions or buffers. Attempting to use these parts with standard carbine or rifle recoil systems will result in damage to the firearm!
NOTE: While the A5SR tube will work on the AR-10 Rifle, the two are not identical. You should NOT try to use an AR-10 tube as part of an A5 Recoil System.