Definitely look like they'd expand pretty well even at a lower fpe. They seem like softer lead and the walls are pretty thin.You make a great point here.
In my case shooting the NSA slugs in .357cal the slug sidewalls are very thick compared to the NSA slugs in .25cal. That may be great for penetration on big game like a hog, but for smaller game, we prefer expansion earlier. This is the very reason why ammo testing for the type of game you intend to shoot, at the energy level you are shooting it at is so important! I had excellent luck literally decapitating Starlings using NSA .25cal slugs out of a 50fpe airgun, but that performance didn't transfer over to the .357cal with the energy levels that my Bulldog can generate. But when I do some ballistics gel test with the FX Hybrid Slugs shooting out of the Bulldog, I expect a ridiculous amount of expansion!
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