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Will very high polished finish on brass cause Excessive stress on bolt face?

 
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Old 03-09-2011, 12:45 AM
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Will very high polished finish on brass cause Excessive stress on bolt face?

I developed 1 load for my 338WM. I wanted the 225gr MRX to go 3,000fps and I got it. That's over the books and must be a MAX load in my rifle.
Did not have standard signs of excessive pressure..the primers look just like the stock WW 200gr cheap'os I used as brake-in ammo...but, a few cases showed slight marks below the belt. Took 9 of them by the gun store and asked couple of the old timers to give me opinions on how close to the edge I was. They agreed with each other that I was most likely getting too much slide of polished case toward rear of chamber and into the bolt face. Seems logical that when ignition occurs the brass is slamed against the walls of the chamber and then is ramed back against bolt face more than normal cause the brass can't get a grip on the walls of chamber cause it's to slick! Just from a physics stand point it sounds correct. That 0000 steel wool made'em look like gold!

I am not looking to go any higher than that load but would like to feel that I'm not
.00001grs of H4350 away from blowing my self up. The most respected reloader said he would reload them 3 more times and then cut one top to bottom to see how much stretch the lower wall had done at the belt.

Also, the Temp was 90 deg. = worse case scenario.

What say you? Did lack of normal friction of case on chamber wall increase the smacking the bolt face took?
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Old 03-09-2011, 01:42 AM
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Re: Will very high polished finish on brass cause Excessive stress on bolt face?

Brass is not slippery on steel. Especially when hot and under pressure. Oil, water or
other lubricants would decrease the friction but not a polished surface. Steel wool does have a little
oil in it to prevent rust so wiping them down with a solvent might help.
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Old 03-09-2011, 06:31 AM
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Re: Will very high polished finish on brass cause Excessive stress on bolt face?

You may want to swab the oil out of your chamber too as long as you are trying to minimize surface slip.
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Old 03-09-2011, 08:59 AM
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Re: Will very high polished finish on brass cause Excessive stress on bolt face?

90% Iso-Propyl (rubbing alcohol) is an amazing grease/oil remover! Maybe too dry after you use it.
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Old 03-09-2011, 09:18 AM
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Re: Will very high polished finish on brass cause Excessive stress on bolt face?

With steel wool polishing you are not even close to the Friction Coefficient range that will cause problems.

Rifle Chamber Finish & Friction Effects on Bolt Load and Case Head Thinning Calculations done with LS-DYNA
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Old 03-09-2011, 01:44 PM
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Re: Will very high polished finish on brass cause Excessive stress on bolt face?

Are these new brass or have they been fire-formed? If they have been fire-formed, did you full length re-size or neck only?
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Old 03-10-2011, 01:10 AM
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Re: Will very high polished finish on brass cause Excessive stress on bolt face?

These were New WW fired once in load development and I only do neck sizing, which had been done to true up the dings of bag shipping.
My "C" drive crashed last month and I lost my master Load file but I have the EXL sheets (somewhere) that I printed to use at the range for data collection but, I am going from memory now, and they all occured from 72gns to 73.5grs of ladder testing and with .0005 to .0020 off the land testing. I remember finding no absolut cause....it just showed up at different times.
When I fired one shot I took it out and used the Mag.Glass on it to see if any thing was going on. I know it is a hot load. I will not fire alot of these hot rounds and eat up my throat but I wanted 3k and I got it.

I hunt with "The First Shot" as the long hot load and the ones in the clip are all std mfg length. Like Grandad told me 60 years ago - The first shot is the important one - the others just make him run faster, as I was emptying his new 22 nylon Rem at a rabbit. He was right, at least for me.
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Last edited by T3-OleMan; 03-10-2011 at 05:42 AM.
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