I want to say that yes, Hydra-Matic A1 lowers were/are used. I've seen that listed on Sniper Central, Arfcom, and clonerifles.com. There's a possibility that Harrington & Richardson lowers were/are used too but I'm not sure. I wouldn't see any reason why the SEALs wouldn't use them, at least. Out of 246K H&R rifles made, surely a couple found new life?