New member, so bear with me. My wife got me a Winchester model 1000 .177 air rifle awhile back and I've just started using it. Sighted in the iron sights & then started plinking and had fun for a couple of days, then couldn't hit anything. Went back to a paper target and saw my group was off the the right. Sighted in again and had accurate fire for a couple of days and then had to sight in again. Don't know what's going on, but assumed the rear sight gets bumped and out of whack somehow. Thoughts? Suggestions? Thanks.