Thank you for the post on the airgun subject! I have experimented extensively with casting for airguns, but only for a few spring type and the Sheridan blue streak, which are all quite anemic compared to what you are playing with. The airguns I've made molds for 177, 30 and 22 caliber, all designed for swag ed hollow base projectiles, and I haven't been able to match performance of the better factory offerings.
For the type of high pressure airguns you have, which are designed to shoot bullets, I can offer considerable improvement in performance. Probably in the accuracy department, but certainly in the velocity and terminal performance areas. Following are my reccomendations.
Contact me by email at LBTisAccuracy@Imbris.net and I'll work a mold deal (substantial discount) with you for experimentation purposes, and this offer is open to anyone wanting bullets for an air rifle of this type, any caliber down to 22, with the stipulation that any others interested in this offer must have a chronograph. Understand that what I sell you won't be just an experiment, but a super performance bullet, as I KNOW real close to what the requirements are. The object is to know how much performance advantage is obtained so readers can know what is available and obtain the same. So it will probably, be a one shot offer with each caliber someone writes about, so I can offer a full line of airgun bullets. I know there is quite a range of calibers up to 50 at least. It will be my option as to how many molds I make for any caliber, but all can be assured of a high performance bullet.
Don't even bother experimenting with hard cast, or with bullets with strong enough bearing to be usable in firearms. They will cause a barrel drag that will reduce velocity dramatically compared to a properly designed dead soft bullet. By dead soft I mean commercial pure lead with a small amount of silver bearing no lead plumbers solder added to improve castability.
You will NOT get expansion using pure lead at these velocities. Terminal performance will be determined by diameter of the meplat.
Great weight isn't important, but better to stay with something around 200 gr, or even 180 gr, in 45 caliber, and higher velocity than bog the velocity down with 50 gr more weight. Penetration will not be a concern. You'll get all the power available is capable of delivering on game the gun is capable of taking on. Game size being one of your questions. Use it for anything the 45 ACP will handle. i.e. Hogs, deer of any size and smaller, keeping shots in the ribs for easiest penetration, and don't take on boars larger than maybe 250 pounds, because of the heavy gristle plate armor on their ribs. Or brain shots from the side or if the forehead is presented reltively flat. (A hogs skull is quite thick and angled steeply, same as a bear, and can deflect even high power rifle bullets.
Because of the arched trajectory, range must be close enough for precision shot placement, and personal experiance must be good enough that you know the animals soft spots. You can deck a 2000 pound butcher bull with complete reliability if the shot is placed squarely on the forehead, centered by drawing a mental X between eyes to top corners of skull. Most butchers kill them with far less bone crushing/penetration power than you have.
No cast bullet, regardless of hardness will have any damaging effect on your rifling. The hardness factor of concern is bore friction alone, which MUST be minimized to obtain optimum power. In the airguns which I named above as my experimentation, hard bullets won't even make it out the bore, and even stick in the chamber without moving. This with the RWS capable of pushing its swaged soft pellet out at a claimed, and VERY effective 950 fps. It will shoot completely through a full grown skunk and kill them instantly! I foret the weight but 17 or 20 grains seems right. You have 10 times that at similar speed!
