Opinions on this.. Air gun?

[Maverick223]

My idea was to get a 405 grain hard cast out of the muzzle going about 1500fps

I was talking about 1500fps, and using a large enough properly shaped venturi orifice (much larger than a Qwaker ) I feel certain that it is possible. The number of shots would be substantially reduced in the process, possibly to a single shot, but I wasn't worried about that. Though I understand why you doubt the design, because "3-5kpsig is a far cry from the approximately 30kpsig of a 45-70"...that is not entirely true because the orifice multiplies the pressure and the only limiting factor is the volume of gas. This is similar in principle to putting your thumb over a water hose to increase the pressure.

 

[Ned Kelly]

That doesn't tell the whole story of it either. The momentum they develop is disproportionate to the kinetic energy relative to a firearm. They get that 550 ft lbs with a heavy bullet at a low velocity so the penetrating power is much greater than you would get from a firearm with similar power.

I was going to mention that as well but I know that some people are sensitive on the momentum and Knockout issue *looks around*

It is around 50 lb ft per second of momentum.

About equal to a .25-06 in momentum.

Taylor KO = 18 est. (equal to a .308)

I was talking about 1500fps, and using a large enough properly shaped venturi orifice (much larger than a Qwaker ) I feel certain that it is possible. The number of shots would be substantially reduced in the process, possibly to a single shot, but I wasn't worried about that. Though I understand why you doubt the design, because "3-5kpsig is a far cry from the approximately 30kpsig of a 45-70"...that is not entirely true because the orifice multiplies the pressure and the only limiting factor is the volume of gas. This is similar in principal to putting your thumb over a water hose to increase the pressure.

With air rifles (I think) it is generally easier to push a heavy bullet slow than to push a lighter bullet fast.

So you could go up to a .50-75 caliber with a 750 grain bullet and try to push it at about 800 fps or something might be easier to accomplish. I guess the air gun guru's know more than I though.

 

[Maverick223]

generally easier to push a heavy bullet slow than to push a lighter bullet fast

Never thought I would hear about a .45cal being too small

.50-75 caliber with a 750 grain bullet and try to push it at about 800 fps

Have to go to about 1100fps to get similar muzzle energy, although I believe that the TKO factor would be a bit more, but the SD would be less (haven't calculated but sounds about right).