Pellets/slugs, relatively low pressure compared to 17Kpsi in a .22LR, blow by are odd internal ballistics.
Theoreticall a slug only needs 0.0005-0.001" engagement from rifling. Our LW barrels have about 0.004" deeper grooves. That's a lot of blow by. Lost pressure/efficiency.
I just tried .217" JSB Knockouts mic at .216-.2165" in my LW Condor. No preload and 2300psi got me 1030fps w/ a .188" top hat. I've sent 32 grain .true Griffin .217" at 1070 but they're fine at lower speeds.
Swaged is good for mass production or by hand. But cast with driving bands reduces friction. And again, if anyone thinks that cast slugs stink, well, everyone's barrel is different but;
https://www.pyramydair.com/blog/2012/03/lasso-2012/ When you know how to cast right and hand lap. These 420257's from his build proved 1/8" moa consistently all day long.
I'm actually suprised the pellets/slugs that fall back out of some barrels shoot as well as they do.
Other airguns I have need a 5.53/5.54 pellet or groups open up.
I'm wishing SAAMI type specs would be initiated but until then? Test test test.