Also known as the "Plumbers Nightmare" for it's odd-shaped tubular reciever, (which may explain the "water pistol" designation.) and a pain in the butt take-down sequence.
If it's marked 9mm/38, it has an extractor setup for a variety of rims, and that's what headspaces the shorter rounds. This can make for unreliable ignition. Extensive use of shorter high-energy loads like the 9 mm para. can cause chamber rings, a la .22 shorts in a long rifle chamber.
DO NOT-DO NOT-DO NOT! run .38 Super through that gun. Super is well documented to CRACK SLIDES in Astra 400's with extended use. It is to hot a load, and the resulting slide velocity in a blowback gun is too high.
A self-discovered "gunsmith kink" re: take-down. The front collar around the barrel must be compressed, and the outer collar rotated 90 degrees to remove the recoil spring. Since the inner collar must be compressed against that garage-door sized recoil spring, this is a great place for torn fingernails or scratches when something like a screwdriver slips.
The easiest way I've found to press it down is an empty .50 A.E. case. It slips neatly over the barrel, which aligns the case, and it gives you a broad, easy surface to push against. It's almost like it was made for the purpose, it works so well.
But I've found that routine cleaning is easily accomplished without removing the recoil spring. The slide holds it captive during regular field stripping. but it's sure nice to know an easy way to deal with it if you want to install a new spring, for instance.
BTW, I have an Astra 600 9mm para., which I really enjoy. It's very accurate for a fifty year old autoloader. Fixed barrels are good like that.
FWIW, Federal Arms makes drop-in barrels in 9 mm para. for the 400, they run $79. The magazine should work just fine with no modification, if you go that route. If you do, ammo cost savings will pay for the barrel right quick.
