Just posted some of this info on hk91.com. I bought two cases of SA from AIM Surplus in Nov or Dec. I am not home at this time, so I do not have the lot numbers in front of me, but one ended in 03/81 and the other in 11/81. Both of these lots give a tar like residue in my PTR 91. Another fellow posted a lot number ending in 07/81 as causing this tar also. So maybe lots from 1981 are the problem. I have notice that the residue sets up as my rifle cools down. If I shoot for an extended session, the tar remains more liquid. If I take a break from shooting, it seems to harden. The ammo is accurate, but definitely for range use only. I'll keep my Portuguese laid back for serious stuff. By the way, I normally can get my rifle cleaned and ready for the next session in about 30-40 mintues. I use the E&L Manufacturing breech brush, a .30 cal bore brush, and Hoppe's. Hope this info helps some.