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Burr in chamber/pressure issue

 
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Old 03-24-2014, 04:59 PM
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Join Date: Oct 2012
Location: Montana
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Burr in chamber/pressure issue

I bought a Ruger M77 mark ii 7rem mag about a year ago. I wasn't into reloading at the time so was shooting factory ammo and tossing the brass when I was finished.

I started getting into reloading in the fall and that's when I noticed that my brass had some pretty good scratches almost the full length. I was also having a hard time opening the bolt, not so much with lifting the bolt but more with extracting. I took the bolt off and shined a flash light down and could see a burr in the chamber. I bought some flitz bore polish and drilled and tapped a new piece of brass, threaded a rod to the end of it and gently worked the chamber with a light coat of polish on the case. I cleaned out the polish and from what I can see the burr is gone and the chamber looks clean and smooth.

Also some of my primers were flattened a little even tho I was well under max load for powder and the bullets were set just over factory spec. Would the burr cause pressure issue on the casing to cause that? I assuming the that bolt not opening was also caused from the burr?

Thanks
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Old 03-24-2014, 10:07 PM
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Join Date: Apr 2007
Location: Fort Morgan, Colorado
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Re: Burr in chamber/pressure issue

No, the burr in the chamber would not cause excessive chamber pressure. Seating the bullets out so far they encroach on the rifling may have caused flattened primers. I think you should test your barrel to see just how far off the lands you are loading these bullets. You don't say what your load is or even what bullet you are using, but if you are using "cup and core" bullets you need to seat them at least .010" off the lands in this cartridge, and if they are mono-metal bullets they need to be seated .040" - 050" off the lands. If you would post your loading info I am certain that others who reload for the 7RemMag could give more information.
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Old 03-24-2014, 10:33 PM
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Join Date: Oct 2012
Location: Montana
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Re: Burr in chamber/pressure issue

The load was 162gr amax with 63gr of h1000. I'm not sure what the oal is, I set them so I can just get them in the mag. I've never figured out my COAL. I wouldn't think that a stock ruger mag is longer then it tho, but then again I probably shouldn't think!
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Old 03-25-2014, 08:42 AM
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Join Date: Apr 2007
Location: Fort Morgan, Colorado
Posts: 331
Re: Burr in chamber/pressure issue

RD, I looked up loading data in my fourth edition Hornady manual and it lists 62.2 grains of H1000 as a start load for this bullet in this cartridge. Just how flat are the primers? Are there shiny spots or areas on the case head? Have you shot this rifle since you removed the chamber burr, and if you have, is the extraction/bolt lift stiff? If you could post some pics of the fired cases it might help see if there is a problem.

You can check the maximum OAL in your rifle's chamber by using a spent piece of brass and a new bullet. With your hand crimp the mouth of the case by pushing it against your bench and then with your fingers start the bullet into the case mouth just enough that it won't fall out. Then carefully start the case w/bullet into the rifle chamber and carefully close the bolt. Then carefully extract the case with your hand. Then with your caliper measure the mock cartridge. This measurement minus .010" will be the max COAL length in your rifles chamber, and that is the length I would recommend loading these bullets.
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