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Originally Posted by REMINGTON JIM
Not ALWAYS It depends on how HOT ? PRESSURE your loads are !  RJ |
It is true that it depends on pressure that your load is loaded to. I loaded for the 7mm08 for many years by fire forming Remington brass with a load using Varget and a Speer 110 HP. I needed the extra case capacity of a Neck Sized case and had a couple of very accurate loads using this method. The secret is to work up the fire forming load so that the brass does not stretch past 0.4703" or Saami MAX CARTRIDGE DIMENSION at the 0.200" Datum line. Preferably the pressures of the fire forming load should be 0.001" under that, like most factory loads, as a FL die will likely just barely size the Base datum if you decide to FL size.
If you neck size then your load should be developed with only enough pressure as to not exceed the Saami Max Cartridge dimension of 0.4703" and then that dimension will not increase with subsequent firings as there will be at least 0.001" clearance at the base datum. The pressures will likely be low enough that there is good spring back at the shoulder as well. You may never have to FL size the brass.
As Chuck pointed out the preferred method is FL sizing as described in the video. If you FL size it is possible that brass will not be fully, fireformed to the Shoulder Datum at 0.400", on Factory rounds or properly designed fire forming load. Set your FL die by running it to the shell holder and back out one turn then size a brass and see if it will re chamber. If it does then reload and fire again and FL with die set out. If it does not fit back in then screw the die down in 1/8-1/4 turn increments until the bolt closes on it. Removing the Firing pin and Plunger Extractor help in getting this fine tuned. Once the bolt closes snugly, on the FL sized round, you can use your comparator to record the HS dimension for your rifle. It can then be used to get whatever HS clearance you want which I believe need be no more than 0.001". Your initial load, developed on the first FL sized case, may or may not require further tweaking but you are good to go for many firings on whatever brass you choose.