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  #31  
Old 03-14-2014, 07:58 AM
.Steve. .Steve. is offline
 
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Re: : I have a couple of engineers, mechanical and chemical, in the immediate family. I think perhaps you joke here.

I am sure the pretty terms are all correct. But they detract from the eventual end result of a worse than the normal bad case from this manufacturer.

The third picture gets the idea across a lot better than ductile elasticity or liquid flow by gas cutting.
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  #32  
Old 03-14-2014, 11:04 AM
WindLogik WindLogik is offline
 
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Yeah, it's good to be on the safe side. A loose primer pocket probably isn't going to lead to a catastrophic failure or a case head separation. Likely, the primer will just fall out. Any person that reloads has likely experienced this. It's a nuisance. It's a real pain when the primer falls into the trigger mechanism and jams it up.
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  #33  
Old 03-15-2014, 04:40 PM
DaveHH DaveHH is offline
 
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Another consideration: The absolute back of the case at the extractor groove isn't supported at all. It is actually outside the chamber proper. It relies on the thickness and quality of the brass to survive. A 45 ACP case has a huge area that is unsupported. A fudge on material or quality of the brass, just makes it fail sooner. All military cases of any caliber are very robust at the primer end.
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  #34  
Old 03-15-2014, 09:05 PM
Papahound Papahound is offline
 
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Really got sick when i first read this post - because i picked up 4 boxes a while back for $100 . so today i took a box to the range - and yes with plenty of saftey gear - shot 25 rounds through my Q.H.M.C. without any issues - all primers still intact !! 110gr. ball - lot # bp0810 L -170 . Guess i just got lucky ! Even held a good group at 50 yrds .
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  #35  
Old 03-19-2014, 12:50 PM
rapid86 rapid86 is offline
 
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Quote:
Originally Posted by .Steve. View Post
The next step is a real Howdy Doody. The gas flowing by the loose primer melts the brass case head and then continues to cut the brass case head causing a bigger hole which causes more gas to flow cutting a bigger hole. Depending on when the pressure drops in the cycle, the result can be a good leak or the melting off of the case head. See the picture below.

The rifle would not likely survive and the shooter would be hurt.



None of this relates to nice engineering phenomenon or pretty terms. It relates to destruction of a case head and a rifle.

I would end this thread here with the idea that the MagTech ammo being discussed is sufficiently substandard that it should be avoided for lack of spec or QC.
Have you ever asked yourself why, when gas leaks past the primer (which is not good) the brass melts in your scenario but the gas, under the same temperature and pressure, doesn't melt out the case mouth?
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  #36  
Old 03-19-2014, 02:40 PM
.Steve. .Steve. is offline
 
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The case head is not fully enclosed by the barrel chamber and bolt. When a gas leak starts at the primer, the gas has a place to flow. Back into the open action. As it flows, it cuts a bigger hole and flows even more which cuts more.

The case mouth is expanded against the chamber and throat, no gas is flowing through a hole in the brass, and there is no leaking gas jet. The gas flow pushes/follows the bullet down the bore.

While the gas cutting is most dramatic in large volume high pressure cases, I once had a leaking primer cut a hole in the BOLT HEAD of a No. 4 British rifle. Federal repaired the rifle because the cause was a bad batch of primer metal. The gas jet cut steel and brass in that case.

My point being simply to avoid poor quality contol once identified.
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  #37  
Old 03-19-2014, 04:21 PM
.Steve. .Steve. is offline
 
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Or if that makes no sense, make yourself a little mud dam like a cereal bowl. Fill it with water until it flows over. Where the water merely pushes against the side, you have a dam. Where the water first overflows, it cuts the sidewall. Compare that to the blown case head photo above. You have now seen fluid dynamics in action.
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  #38  
Old 03-19-2014, 09:22 PM
WindLogik WindLogik is offline
 
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So, a loose primer pocket ususally does not look anything like that picture. Usually, the primer just falls out when the case is ejected. Not that big of a deal.

If there is a path for the hot gasses to escape at the case head, the reason the case head melts is due to increased heat transfer to the brass. When you have a very small gap and a very high pressure, you get an extremely high fluid velocity. When this happens you have a high amount of local heat transfer that can melt the brass.

The same thing happens to your throat every time you take a shot. While the bullet is being seated, combustion gasses flow past the bullet in the very small gap. The occurs at a very high velocity. Again, increased heat transfer to the throat of the barrel erodes it a small amount with each shot.

Heat transfer from a fluid is complicated. But, usually impingement and higher fluid velocities lead to higher heat transfer rates.
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