Hunt30-06 said:
Federal primers are a few thousands of an inch larger in diameter than all the other primers.
Primer pockets from the major manufacturers are ±0.0004" or ±0.0005". Primers themselves are likewise with tolerances of about half a thousandth. 0.01746" to 0.1751" is the standard range, however, they can be out of round by up to another half thousandth, and if you measured the longer dimension you might be confused by what the dimension actually is. Also, the average person using a caliper cannot get an accurate measurement this fine, and an OD thimble micrometer has to be used. Caliper measurements can err up to two thousandths fairly easily at the hands of those without tool room experience. Federal primers are among the easiest seating primers in any size, so the idea that they are several thousandths oversize is not remotely feasible.
The issue with Federal brass is that it is "low brass" of 80 parts copper to 20 parts zinc. So is Remington brass, by the way, but it is work-hardened more than Federal. Federal has found that softer brass improves accuracy by allowing pressure to self-center the brass more freely in the chamber, so they do this on purpose. Their primary objective is accuracy, not reloadiablility. The problem experienced by some shooters with this is that if they load to their rifles to near peak pressure limits, and at those pressure Federal brass can expand too much to be reloaded again. Indeed, some Federal factory ammunition in Magnum chamberings has been found to eject with the primer already falling out of the case, as the case head has expanded beyond the normal tolerance range at that magnum pressure.
That same softness, however, has an advantage. It doesn't harden and split as easily as some other brass. The trick is to avoid loading federal brass all the way to maximum pressures. If you just use it at moderate pressures, it lasts a long time and works very well. In pistol brass, as long as you are using a chambering that is not extremely high pressure, Federal brass is really great. It seems to tolerate resizing an almost unlimited number of times. I have personally reloaded both Winchester and Federal cases over 50 times in .45 ACP loaded to target pressures. This was Winchester brass from the 1980's, before outsourcing was so common. I can't speak to how it holds up today. It was genuine 70% copper, 30% zinc cartridge brass back then.