I think you must be referencing the LAR-8 Advanced Half Quad. The old version weighed 21.3 ounces on the Mid-Length and 28.6 ounces on the rifle-length. The current models weight 14.6 and 18.4 ounces respectively.
On the TROS, 15.4 and 22 ounces (mid/rifle).
On the DLXs, 14.5 and 21 ounces (mid/rifle).