Specifically, can Speer or Hornady round balls that are supposedly 100% pure swaged lead be used in airguns without damaging the guns? I want to shoot them with airguns that have bore diameters of .457 (45 cal) or .495 (50 cal). I don't like the quality of many airgun bullet maker products that allow untrimmed sprues or poorly cast balls to be sold as first-quality ammunition.
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I have done that in my Quackenbush rifles and done no harm.
As long as you KNOW the real rifling dimensions, and stick to the +0.001" rule, you will be OK.
Balls should be shot from rifles with slow twists (1/50" to 1/66"), while slugs may require faster rifling.
SOME barrels with fast rifling WILL shoot round balls accurately, but this is the exception and not the rule.
As far as Fluid Dynamics go, uneven/rough surfaces and, even sprues if properly oriented, do not detract from the exterior ballistics or the accuracy of a system. But it all depends on the quality of the LOADER himself. If you find that your projectiles are undersized (up to 0.004" short) try "screening" the balls and you will get a better fit as well as better downrange ballistics, "screened" balls do require more careful loading, especially in a muzzleloader, but in an airgun, they should do OK with a bit of rough handling.
SOME big bore airguns have a long forcing cone, not all. In these cases, a slightly oversized projectile can be used, but only a chamber cast, or tests, will show you what works and what doesn't.
I have shot even jacketed 9 mm's bullets out of 9 mm's airguns, but the accuracy and power delivered were not quite what was expected. Remember there is a finite energy available in an airgun, and part of that energy is used when swaging the projectile into the rifling.
Be aware of the risk of getting a projectile stuck in the bore and have a BIG caliber-appropriate cleaning rod with a brass tip available and ready to be used (for big bore airguns the fiberglass/plastic loading rods they sell for muzzle loaders work well). Usually, a light tap with a small hammer will dislodge a stuck ball. Slugs may take quite a bit more force.
So, get to know your barrel (slug the barrel with an appropriate sized pellet and measure the twist) and then decide what you want to do.
HTH, keep well and shoot straight!
HM
Hornaday 145 grain round balls worked well in my 457 Element Max. Not as good as slugs but ok. For slugs I've shot NSA and Griffin with very good results.