There have been many tests done firing different type of pellets to dense putty material, soap (to examine exit hole) and even crows.
The most popular pellets like the harder lead alloy Crossman Premiers deform VERY little if not at all after they are recovered. Even the Kodiaks and most domed pellets do NOT mushroom hardly at all. They have more penetration than the Crowmagnum hollow points and all other HP pellets.
We are not questioning the penetration capabilities of the high velocity lighter PBA's (at "close" ranges anyway), but more the damage that can be done to the barrel and more specifically the rifling of the barrel. There has been much discussion on this topic and even the airgun experts and airgunsmiths say that the rifling is made for lead pellets. It can be otherwise damaged by non-lead ones. There has also been much discussion on penetration vs. Energy or knock down power - FPE. Lighter pellets do not have the "punch" that heavier pellets possess by the laws of physics. They also lose a lot more energy farther out than the heavier pellets. Pro Airgun hunters prefer higher FPE #'s over velocity to knock down their prey, which is why they always opt for larger caliber and heavier pellets when hunting. In several studies, they showed that faster traveling lighter pellets tend to go right through most animals carrying much of the energy with them after exiting. Whereas the heavier pellets expend much of their energy inside the animal causing more damage and shock to the animals. In a gun like the 350 (I own one in .22) that has a lot of power, it probably doesn't matter what pellet you use. Your prey will go down no matter what, because sufficient penetration will occur with any pellet, light or heavy, even with a 21gr one. I shot a squirrel at 40yds and the pellet still went through his body via the upper shoulder area which seems to be thickest and has more bone structure! Another 14.3 Crossman Premier (14.3gr 22cal) went right through a Groundhogs head (and they have big hard sculls twice the size of a squirrel) at 27yds and 30.5yds out (2 different Ghogs). At 34yds, a Kodiak went right through a G-Hog's neck breaking his spine but that's softer than their head.. There is no need to use the PBA's on a UltraMagnum 20-21 FPE air rifle (I assume you have the .177, .22 cal is 22-24 FPE). I am truly amazed at the power of the 350 springer. The truth of the matter is, the larger the pellet is, the more damage it inflicts, and if it increases its diameter a little by deforming its softer lead compound, then the bigger the wound canal is, the better.
In a less powerful airgun, I can see using the PBA's sometimes to get an extra milimeter or 2 of penetration and that much needed higher velocity than you can't get with regular weight pellets, but continuous use of non lead pellets will result in less accuracy by your barrel over time. This doesn't happen after shooting 20 or 30 PBA's but takes time and is very gradual so that you don't notice it as much at first, until after you 've shot 500-1,000 or so and start adjusting your scope thinking something must have moved..
I 'll bet you any amount of $$ that a 350 with a heavier pellet can drop that beaver or mink out at 40yds, while your PBA will just wound it because it would have lost so much energy it wouldn't be funny..
Look at this 350 stats link:
http://www.straightshooters.com/ourtake/ottest350.html
Take note of the 2 lightest pellets tested, the Laser & Hobby (in any caliber) and see how much faster they are at the muzzle than an any other pellet but lose tremendous amounts of velocity and energy at 25 & 50yds. Then take a look at the CP light which is only 1gr. larger and see the difference. Then look at the even heavier pellets like CP heavy or CP Premier in .22 (JSB exact, etc.) which have TWICE the energy at 25yds and more than twice at 50! Their velocity is even greater at 25yds than all other lighter pellets that started off with 100fps more velocity.
My guess is you took that beaver at a distance of less than 20yds. At 40yds, the beaver would 've felt a sharp sting and run away with that little energy the lighter PBA carries, unless it went right in the heart through the softer chest area and in-between the ribs.
