I too have found that with some load combinations I can't rely on the first and sometimes not the second shot from a clean barrel hitting in the same spot as the rest. With those loads I always shoot a squib load of a cleanshot pellet (I have some left over from years ago) and an empty sabot packed with patches. This gets me a fouled bore that is more or less non corrosive. I prefer to find loads that will work without throwing the first shot but sometimes I can't find it in time for the season.

Tom,
I do a similar thing with my CF's in that I don't clean it after I sight in until the season is over. I know of a hunter whose 270 shoots a foot high and a foot to the left on a clean barrel and slowly walks in to dead on by the 5th shot. Despite several people telling them about this they insist on cleaning the gun before going hunting. A couple of years ago they shot at a nice CO bull only to make a bad shot and lose a wounded animal never to be found again. This is unacceptable to me, I want to know exactly where my bullet is going to go when the gun goes off.