Never done it myself to check it but was told by an old timer that accuracy from a rifle can only be measured
from a just fouled cold bore. He said that after a few days the fouled bore became hard fouling and would
affect your first shot .
Could be lube hardening in the bore; one shot heats it up to soften. Lead rimfire bullets have ‘low drop point’ waxy lubes.
When I pattern ammo it takes 5-6 shots of new stuff to condition the bore between groups until group size stabilizes.
Heat up CCI with a hair dryer and see what you can wipe off the bullet. Or put 1-2 rounds in an empty box and heat it - nose down the lube will drip to the tip.
Might also be lube buildup in the chamber - unless your bullet engages the lands this will change cold to hot.
Well I shoot CCI SV and yea my first shot its usually about 1" from where I've aimed every single time. I think, just guessing, its all the dang wax these things are soaked in. I bought 3 cases (15,000 rds from natchezss sale) before the ammo hording crap started and a good chunk of them have excess hardened wax on them. I have problems extracting them as well. Ely and others, no issues. I think it is poor QC from CCI.