Dunno what it is, but over the years I've had a number of .22 rifles that were accurate with LR ammo, but none of them would shoot CB shorts (or longs), worth a damn.
Had a Rem 572 years back that was very precise with CB shorts, but otherwise my experience mirrors yours. Shorts generally fare poorly with a LR chamber. Longs....have been pretty much worthless in my experience. If you missed it, I was shooting with a short match chambered barrel.
