According to Midway USA, a AR Stoner 6 position collapsable stock weighs 16.3 ounces including the buffer tube, buffer spring and carbine buffer. A UTG A-2 style fixed stock like on a M16-A2 weighs 25 ounces. The length of pull is slightly longer on the A2 stock compared to the original M16-A1. The M-16-A2 length of pull is 13.5 and the A1 length of pull is 12.875. I couldnt find a listed weight for an A-1 butt stock assembly and not sure how much difference 5/8 (.625) length would change the weight.
https://www.midwayusa.com/product/1003275040?pid=550882
https://www.midwayusa.com/product/1003275040?pid=550882