I just ordered the 50771 model, had been on the prowl trying to buy a 51660 model since October 2011. But eveywhere I went they were on backorder and had no idea when they could get one. The GS I went to said his supplier had 9 of the SPX, but none of the other 590A1 models with the 9 shot feature. I just hope the front sight is'nt canted.