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Musings on barrel life...

 
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  #29  
Old 03-03-2008, 08:38 AM
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AISI / SAE steel classifications:

41xx - Chromium 0.5% - 0.95% and Molybdenum 0.12% - 0.20%

the xx is the standard notation for carbon content 4150 has approximately 0.5% carbon, 4160 has approximately 0.6% carbon.

The letters CM after the name are a redundancy - they are completely unneccessary, as being in the 41XX family of steels, they are, by definition a CM formula.

Depending on how exatly the steel mill made a particular batch, their quality control, etc, 4150 and 4160 are close enough that they could end up being functionally identical. Certainly, the extra .1% carbon does make a pretty big difference, but standard tolerance levels in carbon content mean that 4150 can have as much as 0.55% carbon and still meet grade, and 4160 can have as little as 0.56% and still meet grade.

In a perfect world, there would be a reliable and stark difference between the two, and steel from hign quality, reputable mills does show a notieable distinction, but that isn't ALWAYS the case.

I've looked at the 5C rifling design. It's an interesting idea, canting the rifling like that. It looks like a sharp cornered version of polygonal rifling, being about halfway from traditional to poly. It seems to offer many of the same benefits of polygonal rifling, and has been showing off pretty well in competition.
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  #30  
Old 03-03-2008, 07:19 PM
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Thanks for the info!
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  #31  
Old 03-03-2008, 10:08 PM
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I can't believe I read the whole thing?!???

It's been a hundert years since I seen those metallurgy terms. I was hoping to see "closed packed hexagonal" in there somewhere. That was my favorite.

That was a heck of a good read.

Here's my experience.

I gave up Remington 40X and Hart Actioned/Hart Barrels and the whole bench rest thing when HK brought out the PSG-1 with the polygonal rifling which would out shoot anything that I had. And that out of a semi-auto.

I shoot a fairly high intensity cartridge with a 3 groove Lilja with, I think, a 1-7 twist. It started dusting lighter jacked, long bearing surfaced bullets at about 400 rounds. I'm told that about 50% of the barrels of this design do the same thing. Its definitely hard on the bullets.

The 5R barrel when rifled exactly right seems to be less hard on bullets.

I'm thinking my next barrel will be the Schneider polygonal in a larger slower twist caliber.

I did some experimenting with Frontal Ignition, igniting the powder at the bullet base, but it appeared that the temperatures increased mostly just ahead of the chamber thing migrated down the barrel. Concentration the heat at the throat seemed to be the opposite of what I was seeking. However, Extreme Velocity Spread and Standard Deviation and accuracy were improved. Plus recoil was noticeably less.

The paradigm may have changed with the newer steels. I'd pay extra for the pluses, if they 'really' made a difference.

Keep up the research.

You post 'em I'll read 'em.
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Last edited by royinidaho; 03-03-2008 at 10:12 PM.
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  #32  
Old 03-04-2008, 06:29 PM
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Sorry, no body centered hexagonal structures here... We're all hoping for the nice, relaxed face centered cubics round these parts! Hexagonal grain martensite is full of nasty stresses that will make your barrel do the twist and other neat things while you shoot!
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  #33  
Old 03-04-2008, 09:43 PM
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On the ship the reactor vessels were 17-4 PH stainless if I remember correctly. Would a little radiation harding be good?

BTW, I don't know squat about this topic. But damn its interesting.
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