I had a problem where a good sized rat had made a nest behind my house.
All I have is a Browning .177 Buckmark break-barrel air pistol that is only able to get about 320-360 fps with lead to alloy pellets.
I needed a pistol so that I could take a quick snapshot at the rat without destroying anything but the vermin. It was a morning routine while it was very cold.
I know I had thumped it a few times with lead pellets, but it kept returning.
So I started looking for something better and found Crossman powershot pellets with a steel penetrator.

I compared the pellets on a used up air freshener can from an automatic dispenser that had pretty heavy steel walls.
Lead just dented one side with a pretty good thump. All of its energy used to flatten the pellet.
The Crossman powershots penetrated both sides of the can when I tested.
Hot knife thru butter type performance, and it basically gives you a sabot round of steel only.
The steel sabot is about 0.125" in diameter that is about 3x as long as the diameter.

I have not seen the rat since my last shot. He either died from my last shot or noticed I really wanted him to move on.

If anyone else is looking for a frighteningly penetrating .177 pellet this may fit the bill.
I have noticed online that they make a .22 call also.

Just thought I would share my backyard review.

Cool. Hope they did the job for you.

I have those pellets in .22. The only problem I've had with them is lack of expansion (obviously) so I feel there is some energy being wasted and not being delivered to the target. That being said I have killed more than a feel squirrels in the backyard with them.