Best .177 hunting pellet?

Are most hunters for small game using CO 2 type airguns or break action spring type?

Almost no one users C02 for anything but plinking. Velocities are often too low and even worse inconsistent because of temperature fluctuations.

I use PCP airguns which have more power, but there are many high quality spring airguns that have the power, consistency and accuracy for small game.
 
Thanks for replying to my question. What spring action can handle large game like deer or hogs? I watched a show a couple weeks ago where they were hunting deer with an air rifle but didn't give any details.

None that I’m aware of. Likely what you saw was a big bore pcp from Airforce Airguns, AEA or one of the others out there that have big bores in their line up. 


edit- I have seen springers take smaller pigs. So that’s doable. But doubtful of deer. Not that a perfect shot couldn’t do it, just illegal in most places and not something most would attempt for a ethical kill. 
 
Peaceful ruler

If you are already using your most accurate ammo and have enough energy to get full pass-through. The ugly truth is about the only thing more you can do is make perfect shots. Don't worry so much about where you hit but more about where the exit will be. Try to make sure the line from entering to exiting runs through the vitals. Even so, only a head shot or wing bone break will guarantee you see no more fly offs. Not long ago I shot several pheasants at point blank ranges. With body shots they flew, when I broke wings they ran. It was only with the aid of dogs I found any of them they were all dead but managed to escape and hide before dieing. That was with a 25 caliber pcp.
 
Changing ammo is not going to make any difference on a less than perfect shot. If your getting full pass through shooting them in the breast. The trouble is not the gun or ammo. Welcome to airgunning.

What do you suggest? Headshots only?

If you are getting full pass through with chest shots, try a better expanding pellet like hades or polymags. Also, try turning down the power so you don't get a passthrough, and you leave the energy in the target.
 
I shot a 177 crosman pointed and a gamo redfire in 177 into ballistic gellatin yesterday. The pointed went through the 9 inch block (was only going about 550 fps) but the redfire only went in a few inches. The "wound path" for the redfire was definitely bigger. Normally I do not recommend expanding pellets but for smallish birds you may want to try polymags, metalmags, and/or redfires (plus the newer Hades). If they will go in deep enough they could give you a bigger wounded area.

Placement is key as has been mentioned. I have hit doves with a 25 and had them fly off. Pretty sure the issue was me. I find it harder to place the shot on a bird. Upper chest seems to drop them quickly, however. Low chest does not.
 
.177 is all about accuracy not knockdown. Though there are some good recommendations on here for which to use every air rifle is different. My Beeman vintage R1 doesnt like JSB hades but is a laser with Beeman Silver Jets or H&N Baracuda Match 10.65 Yours will most likely prefer something different. You just have to keep testing at 30-40 yards.