I think I get better stoppages of squirrels with more penetration. Pass through on side shots with my Prod and penetration the length of the squirrel with a front shot. Head shots that exit. It also likes H&N FTT best, copper plated, so that is what I use. I've compared the size of a 22 caliber hole in a squirrel body to a center fire, expanded, hole in a deer and the pellet covers more of the squirrel body. So the wound channel being sufficient without expansion makes sense. Both theoretically and by experience, domed pellets work well.
In my 25 caliber Avenger H&N FTT don't shoot well at all. It likes JSB Kings, 25.4 and Heavies, a lot. MKII seem to be a little worse than original heavies but still good. But it loves FX 25.4. 1/4 inch groups at 33 yards are fairly routine. Heavies are about the same. I need to shoot it at longer distance and will when I get my tank setup finished so I can carry some air with me, I will. In the yard I am limited to 33 yards.
I've also tried penetration with metal mags in the Prod and a couple different slugs in the Avenger in wet paper. The expansion greatly reduces the penetration. That might sometimes be advantageous but I like entry and exit holes. For that, the domed pellet is a better bet.
But if the Avenger really liked an expanding pellet or slug, on small game it would have sufficient penetration and I'd probably use it. Accuracy is king for air rifles. We must place the shot well to get clean kills. My Prod is tuned to about 18 foot pounds and at that power level I do not want to reduce penetration with an expanding pellet. The Avenger at 50 ft lbs has enough that I could probably use an expanding pellet but on small game a 25 caliber hole is even better than a 22 and the 22 works well. So I do not feel like I need the expansion and I haven't found a slug it likes.
