I got the chance to do a little playing with the .380 Bore FH today.

Last week I took one of the original old red, plastic empty shells to a machinist. He ran me out 3 samples. 2 in brass and one in aluminum. All of them work well. But the aluminum is just handier due to the light weight. I will have him spin me out another 10 or 12.

I loaded up all my plastic empties and the new metal ones and shoveled the snow off the front porch enough to set up the chrono. I got some random and freaky readings. Probably due to the patch material or condensation cloud from the CO2 or both. But, the overwhelmingly consistant figure ran right in the 360 fps neighborhood. "Not very fast" one might say. One would be right. But that's for a 63.5 grain projectile!! Holds right at 18 ft/lbs. I got about 20 full power shots before the CO2 cylinders gave out.

This oughta be quite the effective stopper on a charging spidey, eh Larry??

Possibly temperature, CO2 is way too temp sensitive for any real accuracy. Every shot changes the temp and pressure in the cylinder.
Your first shot may have 1500 lbs pressure, but 3 later you've got 800.
There is a Little brass air tank that replaces CO2 bulbs but it's not too useful, if you put enough pressure in it, you can hardly fit it in a CO2 pistol as there is TOO MUCH force on the valve.
I did convert a Ratcatcher by fitting one in the gun then adding a filler port so you didn't have to remove the Air cylinder to fill it up. It worked OK but a lot of hassle for a Ratcatcher.