#11
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I have a Cooper 38, which I'm guessing is similar. It has very little primary extraction cam. I've been meaning to tig weld a blob on the bolt handle and reshape it to get a little more. If you close the bolt on an empty chamber, then push the handle forward and lift it, how far back does the bolt actually move? |
#12
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The only resistance on the lift is the final 1/8" or less. I messed around with some formed, but never fired cases last night. Guess what? They cycled just fine. Looking like everyone who mentioned growing brass and the need for a small-base die are almost certainly correct.
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#13
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I never did like the stiff cock-on opening of my Cooper . |
#14
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1. I really did not want to believe my brass was growing. It has never been an issue before. 2. I believe it is limited to one particular lot. I always start with the same brand new .223/5.56 cases but purchased over a period of five or six years. 3. I have cases fired many times that did not exhibit this behavior on their last firing. I need to pull them out and see what happens. 4. The difference in size is very hard to pick up with a pair of calipers. Could be that my chamber is on the tight side and unforgiving of any growth. 5. I will be loading some of the unfired cases and making note of the results. 6. If an occasional trip through a small-base die is needed, well, I can live with that. 7. Will also visit with the Cooper folks if they return my call next week. |
#15
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Sounds good.
I had a similar "sticking" problem, and with a tenth carbide tipped Micrometer ( not vernier) it was difficult to determine if the non sticking vs sticking cases were actually different sizes to prove that was the problem. I think an egg shape was more the culprit than diameter average as rotating the cases while feeling for drag made my head spin. I do have a 223 small base die I should dig out and see if that reforms some of the brass. Allen |
#16
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I had the same problem with my 6mm Cooper. After a few firings on the case, it would be difficult to open the bolt. I found that the area above base was growing slightly after each firing and the FL die was not sizing that portion back down when running the case through the die. I was able to purchase a "ring die" made for that caliber (Accurate Shooter web site) and using it sized that lower portion of the case solving the issue. I now measure each case after firing and FL sizing and know the parameters when the ring die is necessary.
Interesting that I am not the only Cooper shooter that has this issue. I'm assuming it has something to do with the way the chambers are made. Keep us posted when you get a response from Cooper. |
#17
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I did load and fire two previously unfired cases last night and everything was smooth as can be. I will be ordering a small-base .223 Type-S die. I figure my oldest boy can make use of it if his black rifle dream ever comes true. That will probably happen immediately after he receives harvest wages this year!
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#18
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Cheap check?
Try running the fired brass through a 221 body die. This should reform the base but leave the neck alone. Start not going quite to the base and work down until the problem stops. I have several 20 VT Coopers and have not had this problem. Could be a misinformed chamber that has a bulge somewhere. Cooper is not immune to this problem. In the past, early times, you could tell when the rifle was build as there was a caliber indicator in the serial number. Be interesting to find out if your and the rifle belonging to 37L1 were built with the same boring protocol near the same time.
Alex Last edited by Alex; 07-07-2018 at 03:57 PM. |
#19
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I think it is how they do the extraction cam, or rather don't. They have a circular cutout at the back of the receiver, and a smaller radius on the root of the bolt handle. These two surfaces sort of hit, or miss, depending on the particular rifle. This doesn't work well. Most receivers in this price range have cam surfaces that give the bolt handle a large mechanical advantage. I have a BAT receiver that will tear the rim off of a stuck magnum case easier than my cooper will extract a tight Hornet case.
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#20
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It will still be interesting to see what Cooper tech says when they get back to you. I've had over 14 Coopers over the years and have had a few issues. It is definitely dependent on the tech that helps. Had one bad experience, had to hire an outside smith to identify and document the problem before Cooper would address it, shipped it to them many times before it addressed. My experience has led me to believe its a great Montana low key easy go company. Probably doesn't have a lot of corporate structure just build nice rifles.
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