Quote:
Originally Posted by lclund1946
It is more likely a combination of over pressuring the brass, which forms it to a chamber that is likely over Saami Minimum, and sizing it with a FL die which cannot be set so it does not oversize the brass. It has been my experience that Federal brass holds much less powder than most other brands. A properly FL sized Federal Brass holds about 1.2 grains more powder than a Winchester brass in a 270 Winchester that I have been working on. This can result in a much higher pressure as the powder is comprssed in the Federal and not in the Winchester and this would show up on a chronograph. Aslo case dimensions may be smaller resulting in more case stretch.
It is commonly thought that setting a FL die to "Bump the Shoulder a few Thousands" will solve problems like incipient head separation that you experienced. However it only reduces case damage caused by excessive HS and not the excessive stretch at the neck, shoulder and base of a case. Neck Sizing solves this problem, except for the neck, but only if one does not overpressure the case so that it is sticky at the base.
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I had a once fired 223 Winchester factory round and an IVI once fired round and decided to measure them before and after FL sixing. I set my RCBS FL die to size the brass with Zero HS, as measured at 0.330" with a Hornady HS Gauge. They both measured 1.458" which is under the Saami Minimum 1.463". The Winchester brass had minimal stretch at the neck, shoulder and base datum compared to the IVI which was near or over minimum Sammi spec. The IVI case was bigger by about 0.005" at these three points. The sizing die reduced the base to 0.3735" on the IVI Brass but did not move the 0.0035 base on the Winchester brass. The necks and shoulders both came out the same after FL sizing. The interesting thing is that the trim length only increased by 0.003" on the Winchester brass while the IVI stretched 0.010". It is apparent that the Winchester brass will last much longer than the IVI in this situation.
I necked them down to my 20-223 EXTREME and found that the Winchester Brass trim length stayed the same at 1.750" while the IVI trim length came out at 1.765" or 0.015" longer. I know that both these brass hold the same amount of Powder and that a new Winchester brass , formed to 20-223, has only increased by about 0.006" on six firings moving a 40 V-Max at 3668+ so looks like it does not suffer from being FL sized each firing or being formed from once fired 223 brass.