In case anybody isn't already aware, I am on the "two holes is better than one" side of favoring simple domed pellets for hunting. But that does lead to a logical concern with what the pellet does after penetrating the animal. Could it zipping off and damage something? To get some data I did some tests today. I do not think they prove much of anything but I found them interesting and maybe some of you will too.
I shot through first scraps of luan plywood and then scraps of 1/4 inch thick MDF and measured the velocity after the pellet exited. I will include a picture of my crude "test rig". Essentially this was at the muzzle. My cheap chinese chronograph does not have a remote display nor does it record (at least in a way I can use). So I wanted everything close so I could just look at the chrony and record the velocity. I used the luan to test things out because I only had a couple small scraps of 1/4 mdf. I find mdf to be less variable in results compared to plywood. I used 1/4 mdf because I consider it crudely approximates penetration of a squirrel. My pump up 177 will not shoot through 1/4 mdf and didn't make it past the shoulder bones of the one squirrel I shot with it. But my guns that shoot through 1/4 mdf kill squirrels nicely and sometimes go through a squirrel - but only on a broadside shot. I used my Prod that was shooting 14.66 grain copper plated FTTs at just over 700 fps this morning (it was cool, about 50 F) for about 16 fpe and my P35-177 shooting 10.66 grain H&N Baracudas at about 890 fps for almost 19 fpe. In wet paper the P35 penetrates a little further than the Prod and it retained a bit more velocity in this test too.
The Prod projectiles slowed to about 100 mps or 330 fps going through the MDF. Or about 3.5 fpe at exit. The P35 projectiles slowed to about 525 fps and 6-7 fpe at exit.
I do not worry much about over penetration with these guns. I suspected the pellets would have limited fpe left if they exited and this seems to be the case. I think this overstates the energy they would have typically because the projectiles often so not exit the squirrel. This is probably beyond worst case for the energy at exit. Probably. But could a 7 fpe pellet penetrate something? Yes, I think it could. I don't think it could kill even a small animal but it might break or injure something. But it doesn't have the same risk as it had at exit of the muzzle and distance will further decrease it's energy.
What about my other PCPs with 30-40 fpe? I'm out of MDF scraps at the moment but I think it's reasonable to think higher fpe airguns would also loose 10-15 fpe going through 1/4 MDF and at least that much going through a squirrel. My 30-40 fpe guns do normally shoot through. If they are still carrying 15-30 fpe then they are more likely to hurt something. I thus see a reasonable argument for potentially using expanding projectiles in guns like this to limit the projectile velocity at exit. What I actually do, however, is to avoid shots where there are things in the path of my shot that could be damaged. That habit got pretty ingrained in my decades shooting powder burners.
I thus see expanding projectiles as possibly having a role for higher powered PCPs but not for lower powered PCPs. I don't think we increase the chances of a clean kill with a 10-20 fpe gun by using an expanding projectiles because it's penetration is not going to be too much with a non-expanding one. But for 30+ fpe guns, I can see an argument for making a wider hole instead sending a projectile zinging off with potentially harmful energy left.
I shot through first scraps of luan plywood and then scraps of 1/4 inch thick MDF and measured the velocity after the pellet exited. I will include a picture of my crude "test rig". Essentially this was at the muzzle. My cheap chinese chronograph does not have a remote display nor does it record (at least in a way I can use). So I wanted everything close so I could just look at the chrony and record the velocity. I used the luan to test things out because I only had a couple small scraps of 1/4 mdf. I find mdf to be less variable in results compared to plywood. I used 1/4 mdf because I consider it crudely approximates penetration of a squirrel. My pump up 177 will not shoot through 1/4 mdf and didn't make it past the shoulder bones of the one squirrel I shot with it. But my guns that shoot through 1/4 mdf kill squirrels nicely and sometimes go through a squirrel - but only on a broadside shot. I used my Prod that was shooting 14.66 grain copper plated FTTs at just over 700 fps this morning (it was cool, about 50 F) for about 16 fpe and my P35-177 shooting 10.66 grain H&N Baracudas at about 890 fps for almost 19 fpe. In wet paper the P35 penetrates a little further than the Prod and it retained a bit more velocity in this test too.
The Prod projectiles slowed to about 100 mps or 330 fps going through the MDF. Or about 3.5 fpe at exit. The P35 projectiles slowed to about 525 fps and 6-7 fpe at exit.
I do not worry much about over penetration with these guns. I suspected the pellets would have limited fpe left if they exited and this seems to be the case. I think this overstates the energy they would have typically because the projectiles often so not exit the squirrel. This is probably beyond worst case for the energy at exit. Probably. But could a 7 fpe pellet penetrate something? Yes, I think it could. I don't think it could kill even a small animal but it might break or injure something. But it doesn't have the same risk as it had at exit of the muzzle and distance will further decrease it's energy.
What about my other PCPs with 30-40 fpe? I'm out of MDF scraps at the moment but I think it's reasonable to think higher fpe airguns would also loose 10-15 fpe going through 1/4 MDF and at least that much going through a squirrel. My 30-40 fpe guns do normally shoot through. If they are still carrying 15-30 fpe then they are more likely to hurt something. I thus see a reasonable argument for potentially using expanding projectiles in guns like this to limit the projectile velocity at exit. What I actually do, however, is to avoid shots where there are things in the path of my shot that could be damaged. That habit got pretty ingrained in my decades shooting powder burners.
I thus see expanding projectiles as possibly having a role for higher powered PCPs but not for lower powered PCPs. I don't think we increase the chances of a clean kill with a 10-20 fpe gun by using an expanding projectiles because it's penetration is not going to be too much with a non-expanding one. But for 30+ fpe guns, I can see an argument for making a wider hole instead sending a projectile zinging off with potentially harmful energy left.
