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

 
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  #15  
Old 03-13-2011, 06:01 PM
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Re: Will very high polished finish on brass cause Excessive stress on bolt face?

Quote:
90% Iso-Propyl (rubbing alcohol) is an amazing grease/oil remover! Maybe too dry after you use it.
Check the label!!!! I believed this rural myth for many years before reading the label and discovering that it has about 2 percent oil!!!!


Secondly, I do not understand why a person would try to work up a load with cheap primers and then change primers and believe their load is the same!
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  #16  
Old 03-14-2011, 01:02 AM
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Re: Will very high polished finish on brass cause Excessive stress on bolt face?

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Originally Posted by Buffalobob View Post
Check the label!!!! I believed this rural myth for many years before reading the label and discovering that it has about 2 percent oil!!!!


Secondly, I do not understand why a person would try to work up a load with cheap primers and then change primers and believe their load is the same!
Okay, I will. I would prefer 100% (200proof), I wouldn't expect to find it though 90% is hard enough to find. I've used 100%, and it will eat the nastiest grease off, and flush with water. It's approved for washing aircraft.
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Old 03-14-2011, 01:18 AM
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Re: Will very high polished finish on brass cause Excessive stress on bolt face?

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

I believe the answer can be found here

http://technology.calumet.purdue.edu...%20Chamber.pdf
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  #18  
Old 03-14-2011, 01:46 PM
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Re: Will very high polished finish on brass cause Excessive stress on bolt face?

Quote:
Originally Posted by Buffalobob View Post
Secondly, I do not understand why a person would try to work up a load with cheap primers and then change primers and believe their load is the same!


Bob, I had the following reply ready to post last night but I could not figure where you got that I had used cheap primers.......I may be dumb but I ain't stupid. Then about 1 pm today IT DAWNED (LOL) on me as I reread my starting post. I am so sorry that I got lazy and used the words “the primers look just like the stock WW 200gr cheap'os I used as brake-in ammo...”. I should have said “the primers look just like the factory made WW 200gr cheap'os ($26.95-box of 20) that I used as brake-in ammo......u know Shoot -Clean, Shoot -Clean, Shoot -Clean etc. not caring where they hit as long as they came out of the tube and went into the target”. I bought all the factory made 338WM ammo in the county and at 2 gun shows as soon as I bought “NELLIE”.
Then I found 4 boxes of my favorite round 230gr BLACK TALONS on the web and they were (gold) $70 / box – same lot. Like a duck on a Junebug, I jumped on them same lot - discontinued dudes - real quick just in case she likes them best. And that's why I referred to to the $26.95 as stock WW 200gr cheap'os.


And now my following midnight intended post:

+++++++++++++++++++++++++++
Bob, all my hand loaded 338WM-225gr-MRXs have used GM215Ms-for speed & hopefully accuracy.
Re the oil removal........my gun shop owner shoots in some class, can't remember which, and uses Ronson lighter fluid down the tube before he starts and it serves him well.

A retired Chem Eng was in there when we were talking and he told me he used ACETONE to cut the residuals out for a clean cold first shot. I have had a problem with Nellie on my clean cold first shot and have tried 5 other peoples cleaning process and she don't like any of them.

One of them was a BLACKWATER 308 shooter (three tours) and he came to the range just to help me with some of the long range processes he used. She liked everything he was doing but the first clean cold shot.
I used Ronson in my old muzzle loader back in the day to wash out the gunk in the rain on a 3 rainy-day hunt. I know it will work but I don't know about ACETONE just before you hunt?
I'm going to see if she likes the Ronson for clean cold shot. I'm open to try your process also, if you would share.



Again, I am so sorry I used “stock” instead of “factory made” and thus the above e-pissle.
Have a nice day.
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  #19  
Old 03-14-2011, 02:31 PM
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Re: Will very high polished finish on brass cause Excessive stress on bolt face?

.......“the principal stresses in this brass ring-element are not necessarily the same functions of chamber pressure P(t) as they were previously when we were looking at a ring-element of the case neck. The radial and tangential stresses can be parameterized just as before:
Sr = -P(t), and
St = 2k P(t).
However, the axial (z-direction) stress Sz in the case walls must be reduced because of the presence of the primer cup acting as a smaller, secondary piston within the case head and acting separately against the bolt face. This primer force itself does not contribute to the stretching of the case walls back toward the bolt face, but the force of friction between the primer cup and the walls of its pocket resists any relative motion, including the “pushing out” of the primer cup against the bolt face while the case head is being “held back” by the larger “wall stretching” forces. This primer friction force is dragging forward on the case head, and so it does contribute additively to case wall stretching.
Looking only at the peak forces occurring at the maximum chamber pressure Pm = 57,400 psi, let us define the fraction of the total peak force on the case head Ft(Pm) that is available to stretch the side walls of the case to be another ratio b, such that:
b = [Ft(Pm) – Fppr(Pm) + Ffpr(Pm)] / Ft(Pm) = 0.8010
where Ft(Pm) = Total peak rearward force on case head assembly
= Pm (π/4) D2 = 6282 pounds
Fppr(Pm) = Peak potential primer force on bolt face
= Pm (π/4) d2 = 1988 pounds, and
Ffpr(Pm) = Peak primer sidewall friction force in the primer pocket
= (Cf) (Pm) (Apw) = 738 pounds.
where d = 0.210 inch, the outside diameter of a “large rifle” primer cup, and Cf = 0.30 = Coefficient of friction used in the FEA for the primer cup in the primer pocket of the case head.
Here, we are using the adjusted value, D = 0.3733 inch, for the effective piston diameter inside the case head of our example .308 Winchester cartridge. This value was derived from the proportional relationship between the two effective piston areas involved (and thence the squares of their diameters) and their peak bolt thrust forces at peak chamber pressure:
D = d [Ft / Fppr]1/2 = d [(Fb + Fz) / (Fpr + Ffpr)]1/2 d [Fb / Fpr]1/2. “


Wood, you nailed it with that link. Thanks
That's just what I said in my own redneck way-LOL!
Seems logical that when ignition occurs the brass is slammed against the walls of the chamber and then is rammed 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!” I rest my case!!!!

Thus I am getting extractor marks???? Are they real dangerous if not deep, and only ocassional?
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  #20  
Old 03-14-2011, 06:35 PM
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Re: Will very high polished finish on brass cause Excessive stress on bolt face?

I'm going to be down at Ridgeland tomorrow and then over at Hamilton Ridge WMA Thursday through Sunday.
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  #21  
Old 03-14-2011, 06:53 PM
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Re: Will very high polished finish on brass cause Excessive stress on bolt face?

Here is a better answer in plainer English from Varmint Al's site

Rifle Chamber Finish & Friction Effects on Bolt Load and Case Head Thinning Calculations done with LS-DYNA

showing bolt thrust with varying Coefficients of Friction



"CONCLUSION.... A polished or low friction chamber decreases the plastic strain near the case head and reduces the chance of case head separation on subsequent reloads.

This chart summarizes the bolt load vs Coefficient of Friction between the brass case and the 416 stainless steel chamber's walls. A rough chamber might reduce the bolt load by 1000 pounds but increase the plastic strain in the brass case near the web. Rough chamber finish and/or excessive head space can cause "case head thinning" that eventually results in case head separation on subsequent reloads."

Here is a list of CofF

Friction Coefficient Tests of 416 Stainless Steel on Cartridge Brass

Estimated coefficients of friction used in the Rifle Chamber Friction Analysis

Estimated/Measured Coefficient of Friction (u) Comments Maximum Plastic Strain
(%) Cartridge Case Wall Radial Thinning (inch) Maximum Bolt Face Load (lbs)
0.55 Very rough chamber, rough reamer finish with tool marks 14.39 0.006054 4435
0.41/0.37 Rough chamber finish, 320 grit finish (200 grit) 13.42 0.006328 4386
0.35/0.29 Smooth chamber, 600 grit 12.87 0.006046 4639
0.25/0.27 Smooth chamber, crocus cloth or smoother 11.10 0.005415 4477
0.19/0.19 Polished chamber Flitz 9.69 0.004858 4565
0.11* Probably not possible: Polished chamber, polished brass with grease 7.92 0.004481 4787
0.01 Friction this low is probably not physically possible and would be dangerous 14.17 0.009328 (case head expansion that could cause the case head to rupturing) 7656
0.00 If Case Head Separation (Hand calculation
f = pressure * area) 8785


so I would think your steel wooled cases would not have a coefficient of much less than .3 which would mean you have no chance of increasing bolt thrust to any degree discernible.

After some study I have no problem with polishing cases with Flitz for preservation of the finish and easier chambering



which might put me near .2 coefficient but still not a problem.

I don't have any case head separations (only one a long time ago) because I resize to minimal headspace but given the option of stressing the case with a high coefficient of friction or putting a minimal amount of additional bolt thrust on an action an bolt built to take the pressure, I would choose the latter.

YMMV
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