Hi, Alex,
The Astra 200 and the old Browning 25 and Colt 25 appear similar, but the Astra uses a hammer while the Colt and Browning pistols are striker fired. Field stripping is about the same. Remove magazine and make sure the pistol is empty. Then, looking at the front of the pistol, draw the slide back until the barrel can be turned clockwise and its lugs are visible in the ejection port. Let the slide come forward slowly. On the Browning and Colt, just before releasing the slide, insert the magazine if the gun has a magazine safety, and pull the trigger, releasing the firing pin. (This keeps the firing pin spring from jumping out when the slide is fully removed.)
On the Baby Browning and Bauer, again make sure gun is empty. Pull the slide back until it can be locked in place by pushing up on the safety. Turn the barrel clockwise, as described above, then release the slide, releasing the firing pin.
There is a book series called Gun Digest Book of Firearms Disassembly/Assembly by J.B. Wood that is available at most gun shows or through Digest Books, Inc. Volume 1 is Automatic Pistols.
Jim