I don’t think it is oil that is slowing you down. I think it is the increased friction from the extremely clean barrel. The fouling from the prior jackets will fill any imperfections in the bore making it slick.
When we shoot a clean barrel at 1,000 yard the first bullet down the tube will be approximately 1 MOA lower than the second. I never make adjustments off of the first. Chronograph shows that the first round will be approx. 75 fps slower than the average of the next four.
I have never run a test to see many it takes to get the barrel to settle down. I always shoot five sighters in LG and sometimes I’ll shoot up to seven in HG prior to record fire.
To find out if it is oil residue or just a super clean bore, try this. Clean as you usually do. After running your oily patches through the clean bore, run five dry patches. Then run three wet patches using Rubbing Alcohol. The Alcohol will cut the oil, and then evaporate.