RR is correct. Changing ammo will result in ur rifle shooting erratically until it 'settles in' with the new ammo. I really don't know the reason. Perhaps it is the different coatings on the bullets. I own 4 different .22s and each one seems to have its own favorite brand/load. There are 2 schools of thought on .22 LRs. One is to keep it clean just like you would any other rifle. Second is that you don't clean them and just continue to shoot it until accuracy begins to deteriorate. I owned an old winchester 52 target rifle that I used for indoor smallbore 4 position shooting that I never cleaned and shot only Eley red box ammo. I don't know how many thousands of rounds I put thru that rifle and it would still put every bullet into the X ring if I did my part. My .22s I use for squirrels however get cleaned after every shooting session. But I usually swab the bore with a dry patch and fire a fouling shot prior to a hunt.