The red arrow in the photograph on the left is pointing to the modified section on the PL-259. When I made this solder connection, I intentionally applied a little less solder just for this picture in the hopes that it would further explain the process.
The picture on the right is of the finished product. While it is probably not necessary to solder all four of the holes on the PL-259 connector, I find myself doing it this way just about 100% of the time. Using the oval hole modified PL-259, and possibly with the assistance of applying solder to all four of the holes, I have never had a PL-259 connector fail due to faulty construction. Now I have had to clean the contact surfaces of a few as oxidation slowly builds over the years. To perform that task, I use a Q-tip soaked with DeoxIT.
Taking the above idea and making it a whole lot better.
I received a tip from my friend Paul, K0UYA, that does just that. Paul's idea is to use a fine pitch hacksaw blade or the proper Dremel tool attachment in order to remove all of the metal between two adjacent holes on the PL-259. The slots should be roughly the same size or slightly smaller then the original holes. When done correctly there will be two slots, possibly in the shape of a dog bone each, between two opposing pairs of holes thus producing two slots and two solid areas on the PL-259. The new slots will expose much more of the braid for a "government lab approved" connection and will knock down on the thermal mass of the PL-259 connector for faster soldering, which means that there is much less of a chance to damage the coax.
Paul has informed me that he has been performing this trick for the last 40 plus years with great success. It was shown to him by Mr. Wayne Stensland of Kelly, IA and a former scientist at the Ames Laboratory at ISU. Where did Paul's elmer learn of the idea? Paul suspects that it possibly dates back to a method used by someone in the instrument shop at ISU.