Probably not, but very likely not going to have any benefit. The speeds the slugs need to be accurate and and the ranges that the ballistic coefficient would come into its own are not achievable by break barrels.
Thanks for your replies. I was worried that I might damage the piston seal. My RX2 Beeman sounds like a .22rf and shoots dime size groups at 25 yards Daystate Howlers.
If the guns report is louder with slugs than with pellets I'd be curious as to what's going on speed wise. It sounds like you may be getting blow by on the slug similar to if it's not fully engaging the rifling.