SNIP
So, am I nut to consider this?
Thanks,
Eric

You probably will get a flood of responses, so I'll pipe up once and
then retreat. g

1) John Browning designed the .25 ACP around the smallest-diameter
cartridge (base diameter .278 in.) that he felt would be safe with a
small-pistol primer. The cartridge is semi-rimmed; tricky but not
impossible to extract with a simple extractor.

2) Performance is similar to a .22 LR; slightly better in very short
barrels, slightly less in longer barrels.

3) Machined brass is not as strong as formed brass, so you need
thicker walls if you machine it. 'Better to use existing commercial
brass.

4) If you get fancy and decide to neck it down to .22, watch out.
You'd be getting into some tricky engineering territory, where
pressures build up in a hurry, depending on what powder you use.

5) Black powder is a mess in small calibers. My friend built a .28
cal. muzzleloader years ago, when Douglas still made the barrels, and
had to swab the bore after every shot, because of bore fouling. The
experts here can give you better suggestions but more likely you'd
want to use a pinch of Red Dot or something similar and more modern (I
use Red Dot in my light loads).

6) With very light loads, the brass can go on and on for a very long
time. However, if you go *really* light, you're going to have big
variations in velocity, and can even wind up with bullets that lodge
in the barrel. Don't go too light.

Back around 1990 I designed a wildcat based on the .32 S&W long,
necked down to .20 cal. That's when I learned about pressures and thin
pistol brass. I made a cherry for it on my lathe but I never finished
the gun, which was to be built on a replica Farquharson falling-block
action that I still have. When I learned about how much potential
trouble I was buying myself I backed out.

Unless you want a new, very involved hobby, stay away from designing
wildcats. .22 rimfire can't be that hard to get. Some cartridge makers
stopped making longs years ago because they're unbalanced and
generally give poor accuracy. If you want quiet, buy some classy .22
LR match ammo. You can watch the bullet go downrange and you may have
to look to see if the gun fired. g But it will drive tacks in a good
target gun.
Greetings ED,
Sorry about the long time for the reply. I have been having internet
problems and the problem was finally solved about 15 minutes ago.
Anyway, with the light loads I want to shoot I am not worried about a
rifle that can handle .22 long rifles rounds having problems if a case
I made fails. But maybe there are things I don't know about that could
make the lightly loaded rounds dangerous. So if anyone knows why my
proposed round might be dangerous in either a rifle or a revolver
please let me know. I'm also curious about black powder being so
messy. At the time my rolling block rifle was made I have been told by
many shooters that .22 rounds were filled with black powder. In fact,
a friend of mine has a .22 Stevens tip up pistol and he was warned by
his local gunsmith/dealer to shoot only .22 subsonic or CB rounds
because the pistol was made for black powder filled rounds. Surely
these guns and rifles didn't cleaning after every shot, did they?
Cheers,
Eric