That's a SPR with a 18" barrel and the one before was a "Mod-H" with a 16" barrel. Both Douglas stainless steel barrels I believe.

There aren't any AR types longer than 20" that I am aware of.

The marine corps had a SAM-R (20" heavy stainless barrel) and the ARMY had a SDM-R (maybe a better barrel that's 16 or 18" and a daniel defense free float rail with an ACOG and maybe a trigger replacement as well) but that's about it AR precision rifle wise.