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Posted: 1/29/2015 6:35:03 PM EDT
| So I'm setting up my new Forester coax press using forester n/m full length dies and need to confirm something. My used brass fired from my OBR is 1.627 measured with a Hornaday headspace gauge. My thoughts were to resize to 1.625. After resizing 3 dummy rounds to 1.625 I chambered each in the OBR to check for function and to ensure the neck tension remained consistent. Now the chambered rounds are measuring 1.617. They chamber fine but it appears they are getting pushed back more than what I'm used too. So I'm thinking I need to set the resizing die to size around 1.615 now. It this normal to have such a wide gap in between fired and unfired brass? The OBR has the extran chamber fwiw. |
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No I took the resized brass and tested the dummy rounds to check to see if they would chamber. After they chambered they were measured again and became further reduced.
Fired brass =1.627 Resized brass= 1.625 After clambering the resized brass it was reduced to 1.617. Is it odd to have .010 diff in fired brass from the actual chamber size? I don't want to overwork the brass but it appears if I set the fired brass back the normal .002 I would still be pushing it back more just by chambering the rounds. |
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Were the "sized" rounds that were reduced by the chamber hard to extract?
I an having a hard time grasping how an AR type action can reduce the case size from head to datum by .008 without causing extraction issues. Or chambering issues, one would think that the action would not go into full battery and would be difficult to eject? As for .010 difference between fired and chambered. maybe. See here page 3. http://www.zediker.com/downloads/14_loading.pdf I know this article is about the M14, but the same principles can apply to your AR. When a round is fired in a Semi-auto the case is still under a small amount of pressure when it is extracted, after it is extracted it can continue to grow unlike a round that is fired from a bolt gun. |
| All the cases were measured with the Hornaday lock and load headspace gauge. I measured before they were sized, then after they were sized then after a round was seated then after they were chambered. All measurements were repeated. They were not hard to seat because the 308 bolt has a lot of weight so they chambered fine. They were easy to extract with no more effort than pulling the CH to the rear. There were marks on the brass from the shoulder to about 1/8" towards the case base. |
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Did you allow the bolt to fly home on the empty case? This may cause some "shrinkage".
.002" clearance is insufficient for use in a semi-auto rifle. I use -.004" shorter than fired dimensions for AR style rifles. M1-A's may actually need more than that. I consider -.003" as an absolute minimum headspace clearance between ammo and chamber when loading ammo for semi-autos. It's hard to know your exact chamber dimensions in a semi-auto .308 simply by measuring fired brass. This round gets ejected with enthusiasm causing more stretching than .223. I have to turn my .308 die down hard on the shell holder just to get "just enough" sizing with Lake City .308 brass. I suspect your brass may need to be resized more if simply closing the bolt on it causes it to shrink another .010". SAMMI minimum to "no-go" is only +.004" headspace. A "field" gage represents SAMMI minimum +.010" headspace and should not be fired. |
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Quoted:
Did you allow the bolt to fly home on the empty case? This may cause some "shrinkage". I agree this is most likely the issue. It is what I would check first. I suspect the inertia of the bolt and cartridge is resizing your case when it gets chambered in such an energetic fashion. Try chambering the round manually. Separate the lower from the upper. Insert the resized round into the loading ramp area and slip it under the extractor. Ease the bolt forward guiding the round into the chamber. You will have to close the bolt by pushing on the end of the bolt carrier. It should close almost the same as if there were no round in the chamber. Practice closing the bolt on an empty chamber to know how it should feel and where the end of the bolt carrier is when closed. If you cannot close the bolt all the way, the rounds are too long. |
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In my experience, brand new, unfired brass is actually quite short - shorter than necessary and shorter than you'd want if you want long brass life.
Do the manually chambering test and go from there. You can always sixe, test, resize, retest, etc until the brass fits easily. <-- you do not need a bullet to chamber the brass. |
| Ok so if I were to measure a new FGMM round and chamber it to confirm there is no reduction in case size then I should just be able set my die to resize to that size. I don't see any advantage trying to get as close to actual chamber size. The only advantage I believe would be brass life. Does that sound about right? |
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Quoted:
Ok so if I were to measure a new FGMM round and chamber it to confirm there is no reduction in case size then I should just be able set my die to resize to that size. I don't see any advantage trying to get as close to actual chamber size. The only advantage I believe would be brass life. Does that sound about right? Trollslayer mentioned the fact that all new brass and ammo is way shorter than SAAMI minimum headspace when it comes from the factory. This is part of the reason why cases stretch so much after the first firing. It guarantees that the new ammo will fit in anyone's filthy chamber and fire, it does not promote case life when reloading. It's not uncommon for new ammo to be -.010" shorter than SAAMI minimum, sometimes more. You probably can't resize cases that much even if you wanted to. The dies and shell holders won't allow that much shoulder set-back. It's counter productive to try. Winchester brass is probably the best USA made case available for bolt action rifles. They are thin and have the highest internal capacity of any brand on the market. They are the worse cases for use in a semi-auto because they get dented and mangled so easily. Take ten cases fired from your rifle and measure all of them. Record the range of headspace measurements. Using the shortest measurement you find, subtract -.003" and set your die up to resize every case -.003" shorter than the shortest case measured. Seat a bullet, making a dummy round, no powder or primer. Make sure the dummy round chambers and extracts with ease. The bolt needs to close easily and the round needs to extract without any binding or noticeable increased effort. Removing the ejector from your bolt will help you feel any resistance more easily. You have to have a minimum of .003" clearance, I use .004" for a margin of safety. Don't exceed .005" or you'll shorten case life. |
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