I've shot many slugs out of OEM factory barrels in pcp airguns. Never a problem.
Here'a MY take on slugs v. heavy pellets....diameter plus velocity = performance!
I don't believe you gain that much, if anything, by spending hundreds of dollars on a "slug liner"....when the standard pcp quality barrel shoots them just fine, IF you get the correct diameter and weight to match the output power of your gun! Don't shoot too large, or too heavy a slug in a moderate performance pcp gun. You won't be happy with the results. If your pcp isn't equal to 50 fpe with pellets, I wouldn't waste your money on slugs.
If, however, you have an Edgun long, or a Taipan Long, or one of the other brands with equal performance, then choose your slug weights and diameters carefully. They will shoot fine, but not all guns like the same slug! Start with the lighter, smaller diameter slugs...work your way up to whatever best suits the gun you own! Accuracy/results will tell you when to stop.
It's trial and error with slugs...and how much money you have to spend on bells and whistles!
Not everyone will agree here...your mileage may vary. It's just my experience since 1970 when I spoke with Dr. Beeman's wife on the phone, and she sold me an HW 55 Springer.