Research, friends who have worked at Smith and Wesson and Remington by phone were unable to help. I will start with the back story. This gun and I have not been handloading for a long time but my son and I are sharing a renewed hobby - reloading for accuracy. In time he hopes to invest in equipment to try PRC class events. I merely wish to one hole and varmint hunt. My gun shoots fine - Ruger 220 Swift. He has picked the Remington Mountain version 700 all stainless light barrel in 270 as his learning tool while we gain knowledge in accuracy development. This gun had only had neck sizing done years ago when I shot enough to use for hunting. Now that brass 1) need to resize to chamber good as the taper is tight, 2) full length resizing is what we all do for accuracy. So as I began our first effort I found the dies I had bought and never used for FL resizing were under SAAMI at the tip of taper near shoulder. I sent them back to OEM who replaced with new dies and I began FL sizing but an had added both bullet and case comparators to our tools and found cases were datum/base all different lengths after fireforming. The longest has been proven to be an accurate representation of what is desired for proper head space control. These measure 2.048 ( our comparator is .377, marked .375 and expected to be as target .375 for a 270 SAAMI matched goal, thus 2.048 is relative and would measure a bit shorter but is near SAAMI chamber spec). Adding a .002 thick piece of tape to base of such a shell makes it to long to properly chamber, thus I know 2.048 is a good fireform and would want to resize to 2.046-2.045. Any batch of shells fired with various brass, various powder levels, various jump of lands, and various case lengths all come back with most cases with little change in OAL to datum. Inspection with a borescope shows no obvious issue in chamber. Neck is measured as best I can to be over SAAMI spec in vicinity of .311-.314 in stead of goal .388 +.02. Chamber tip of taper is tight to spec. Head space is tight to spec based on 2.048 cases that have fireformed. Thinking the ejector and claw of bolt was not engaging these short cases when the bullet is chambered until fired, I chamber a short empty case and it has engaged the claw since the bolt pulls and ejects the case - so that is not a contribution. Recent loads were same powder and 6 different land offsets. six rows of spent cases in the box - four rows- primers normal, fifth row had 2 primers hanging out the case a few thousands but no sigh of pressure - good radius on corners. sixth row, every primer hung out between .004-.009". All primers in the box were re3viewed with a magnifier and show machine marked as seen on bolt face center around fire pin center piece. These marks are the fine circular markings of normal course lath turn work and match bolt and spent primers, yet absolutely no flattening and powder levels are 75% of max ( Win 760 ball 53.5 grns on these loads ). Labradar data has proven very good, even on these last loads with one set at less than 20ES, groups however keep getting worse ( wind conditions, temperature and fouling are issues to these latter rounds). Some of the brass - thinking annealing is needed - has been reloaded several times, so this last round were first reloads of once fired Remington factory loads. Being once fired, they had similar variable lengths to the reloads prior which might have been hard. So all brass I have, is exhibiting the same lack of fireforming with exceptions to 2.048. They range from 2.033 -2.048 with most falling 2.040 +-.002. Note now that this difference is about .008 thousands which matches the primer hang out of .008 or so. I think this is key to understanding the issue but have no idea what to do to resolve this so I can FL resize and have consistency. Neck lengths are also not growing and are equally in variance in accordance with what is new at SAAMI and under with a variance fighting accuracy as well. Die button is on the set point of .275 for all loads discussed, although the next round will find that button has been polished to .274 for better neck tension, which might be a mistake for this chamber, as I said, i recently measured the neck to be a bit loose. Your HELP and ideas of how to find this cause is desired, other than barreling this gun, which may not solve it. That said, also is important in case we use this action to make a PRC gun from that action and end up with a repeat carry on issue from the action, not the barrel/chamber. Help this frustrated father help his son!
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