The .22 Long "standard load" is basically the same 29gr bullet as used in the Short except in a longer case loaded for a velocity of roughly 1200fps.
The .22LR "standard" is a 40gr bullet at somewhere around 1250fps.
The higher pressures of the LR cartridge might be too much for older firearms and cause damage or injury if things fail.
CCI still makes a couple different .22 Long loads. Specs available on their site...
http://www.cci-ammunition.com/ballistics/rimfire.aspx
That being said, I have used standard velocity .22LR ammo in .22 Long firearms...in small doses. This was before I knew that you could still get Long ammo, but when I do get the itch to shoot either of my two "antiques" I usually grab a box of Shorts instead.
The 23A is a good strong little rifle. I doubt you'll damage it since later models of it were marked .22LR, but better safe than sorry. (Gee, how well does that fit in with my above-mentioned youth ignorance one paragraph up?
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