When Colt was developing the revolver that became the Cobra they made an experimental prototype chambered in .357 Magnum. Understand that this revolver had a special cylinder, and was not simply a rechambered .38 Special. However other then the cylinder the revolver was a stock Cobra-to-be.
They fired 3000 round of original 158 grain Magnum loads through it - which were hotter then emasculated stuff that’s generally being made today, and while the shooters were badly pounded by the recoil and complained the gun itself suffered no damage nor was the frame stretched.
The Old Fuff in no way suggests that .357 Magnum level loads of any kind should be fired in a Cobra, but on the other hand there is no reason to not carry Plus-P .38 Special loads while practicing with something lighter. As has been pointed out, Colt recommended that if one fired hotter-then-standard loads in any quantity the revolver should be checked out after each 1000 rounds, and even during the 1930’s they suggested that all-steel revolvers (which was all they made) should be returned to the factory for a quick check and possibly a tune-up on a yearly or biyearly basis if they were used on a regular basis. But at the time there were a lot more qualified service centers set up to do this then there is now.
Given that this fine revolver has been out of production for some years, and replacement parts to say the least are getting hard to find, some common sense and judgment should be used. But on the other hand the Cobra isn’t exactly delicate.
