I'm wanting to set my die for headspace but brass is not wanting to stretch in the chamber ? some have been fired up to three times ? Do I keep on firing until bolt starts to get snug upon closer? Been neck sizing only? .280 AI and .300WM
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Brass not stretching
- Thread starter 4darkseid
- Start date
So I am guessing that you are trying to get you neck longer to keep the carbon ring in check. I have not tried this with AI brass, but to get everything else to stretch I anneal, FLS bumping the shoulder 0.003 WITH the dreaded expander button. Annealing will fight the spring back, the 0.003 gets the shoulder back far enough for the next firing to stretch the case body, and the expander button pulls the neck forward. Just be sure to check after sizing as you may find some are already too long.
4dark, expound on what you are doing. Im getting the sense that you are talking about your shoulder to case head measurement? What method are you using to find the dimension?
So you are using your full length die to size just the necks down for the subsequent firings?
If the shoulders didnt grown from factory ammo locations then you have a shorter chamber (not a bad thing if you arent having issues, I would say I prefer it), I would chamber a fired piece and see if its snug, if so size and bump the shoulders back .001 and see, if its still tight go to .002, it should be getting pretty easy at this point.
Or size a couple sacrifice pieces down .005 from what they are now and see if they grow back to the current length. If so then you have your answer as to if what you are observing now is correct.
So you are using your full length die to size just the necks down for the subsequent firings?
If the shoulders didnt grown from factory ammo locations then you have a shorter chamber (not a bad thing if you arent having issues, I would say I prefer it), I would chamber a fired piece and see if its snug, if so size and bump the shoulders back .001 and see, if its still tight go to .002, it should be getting pretty easy at this point.
Or size a couple sacrifice pieces down .005 from what they are now and see if they grow back to the current length. If so then you have your answer as to if what you are observing now is correct.
There are 3 reasons I can think of to want your case to stretch. 1) you are getting / trying to minimize erosion and carbon, 2) the throat is longer than normal and you need the extra neck to seat closer to the lands, or 3) you trimmed too short causing #1 or 2.
Any time I have had one of these conditions I wanted (made) the brass stretch. Just because you can load to keep brass from stretching does not always mean you should be happy that it is not stretching. Sometimes you need to fix shit.
Any time I have had one of these conditions I wanted (made) the brass stretch. Just because you can load to keep brass from stretching does not always mean you should be happy that it is not stretching. Sometimes you need to fix shit.
You said, "I'm wanting to set my die for headspace but brass is not wanting to stretch in the chamber ? "
I interpreted "... set my die ..." to mean that you want to set back the shoulder so that it is .001 or .002 shorter than shoulder length - the standard guideline for shoulder setback.
I interpreted "... brass not wanting to stretch ..." to mean that you take a sized case, measure the shoulder datum to base length and observer X. You shoot that piece of brass and you repeat the measurement with the fired case and it is still X.
I'm not sure I understand the "wanting" part. In my limited experience, cartridge brass has really limited motivation to do anything. You have to hit it with 55,000 PSI at high temperature to get it to even pay attention. Some men and women have reported ex-spouses with similar motivation.
If your brass is chamber length (that is X is chamber length) and your die is not setting the shoulder back, this would be the situation. The brass is X, X is also chamber length, when you fire it it is already chamber length so it doesn't get any longer- voila, no change. If your brass is less than chamber length and you are shooting with low chamber pressure, this might also happen - insufficient pressure to expand the brass. There are probably other possibilities, those are the ones that come to mind right now.
Take a piece of fired-but-unsized brass. Measure shoulder datum to base. Adjust your sizing die so that when you size the brass, the shoulder comes out a few thousands shorter - I think that someone above said .005. Now shoot it. If that case is now .005 longer then adjust your die from there. If it is still .005 shorter than the fired case, I think pressure is not high enough to cause the brass to stretch.
There is an implicit assumption that your tools and your technique are correctly measuring the distance from shoulder datum to the base. I use the RCBS precision mic. When I look into the micrometer thimble I see a large hole and a small hole in the middle of it. When you tighten the thimble down on a case, the case neck goes into the small hole. The diameter of the small hole is .400, the diameter of the SAAMI datum line and is way bigger than the neck. The measurement is the distance from that "ring" (where the case neck goes into small hole) to the bottom of the micrometer. When I am working with this problem, I tumble the brass to make sure it is clean before I measure the fired case length. I have two 308 bolt guns, one chamber is .002 shorter than the other, this means that a cartridge that is right for the short chamber is a couple thousands too short for the longer chamber.
When evaluating whether the brass is actually chamber length, I remove the firing pin and the ejector pin from the bolt. I have extra roll pins. The bolt to case fit is still slightly constrained by the extractor. If I remove that, I have to poke the case out with a cleaning rod so I test a few times to be sure that I am getting the correct feel. If you think that your brass is shorter than chamber length, stick s small piece of scotch tape to the bottom of the case. If the bolt closes on that then the case is at least .003 shorter than the chamber.
Adding to above … when measuring a fired case for headspace, especially one fired in a stock Remington, I find it necessary to remove the spent primer to get consistent measurements. Use a decapping die for this, not the FL die.
