Case head separations are caused by excessive head clearance which means either the rifle chamber is too long in headspace or the cartridge is too short. Headspace or, more properly, head clearance, is also the cause of the excessively flattened primers. I suspect the brass is being sized too much so that the shoulder is being set back. Back your FL die out about a 1/2 turn, size a case, and see if it goes into the chamber with little resistance. If there is some resistance, turn the die in 1/8 turn and repeat the test. Do this until you reach the point where there is just a hint of "feel" as you close the bolt. You can then lock the ring in this position and your brass life will be much improved. The 270 has a decently long neck and some taper to the body so it lends itself well to partial sizing. After I have set the die up as described, I then put a washer which 1/10 inch thick beneath the lock ring for most of my loading (the decapping rod may ave to be turned in a bit). This will really improve your brass life and will reduce the amount of trimming necessary.
A second point which I have to mention is, if you are seeing enlarged primer pockets after just a few firings, the load is too hot for the brass. Pockets may eventually loosen due to wear but this takes a lot of loading. Otherwise, enlargement means the pressures have exceeded the elastic limit of the brass. GD
