Chamber pressure - firearm dependent?


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Matno
November 22, 2013, 03:19 PM
I'm getting back into reloading after a 20+ year hiatus. Haven't actually loaded up any rounds yet, but I have been prepping some brass and noticed something surprising. Factory 308 brass that I fired in my AR-10 has VERY flattened primers. When compared to fired rounds from my other calibers (.223 and .300 win mag), there's a definite difference. These are factory loads (mostly American Eagle 155gr jacketed bullets since the gun came with 400 rounds of those!) that don't seem like particularly heavy loads. Can chamber pressure vary from gun to gun? I assume factory loads would be relatively safe, and all of the fired casings look identical (about 100 of them). Since examining the primers is the main way I know of to monitor pressure, I'm wondering how I'm going to know if I'm loading too hot if even "wimpy" target loads look like that?

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rcmodel
November 22, 2013, 03:33 PM
Yes, chamber pressure can vary from gun to gun..
But what is more likely, primer hardness can vary from one ammo manufacture to another.

Reading pressure by looking at primers is akin to reading tea leaves to tell your fortune.

If you use published .308 load data, and work your way up?

You are very unlikely to get into dangerous pressures.

One thing to watch with your semi-auto it how far it throws the empty brass.

If they land in about the same place the factory loads do, you are likely fine.

If they eject into the next county, you likely aren't.

rc

Matno
November 22, 2013, 05:13 PM
Sounds good. I'll watch the brass landing zone. I definitely plan on starting with light loads and working up, but it's a heavy barrel, so I'm not worried about its ability to handle anything in the range of normal.

ranger335v
November 22, 2013, 05:25 PM
Most flat primers happen because the case shoulders were set back much too far during FL sizing and sometimes factory ammo is too "short". And your headspace may be a tad long too. That stretches cases fast and can lead to a dangerous head seperation pretty quickly.

Back your FL die up a quarter turn, size a case and see if the empty will chamber easily. If it does, back up another quarter. When it won't chamber easily, turn the die down in 1/16 turns (about .0045" per step) until it does. Reload a few rounds and test again, your primers will probably be fine.

NCsmitty
November 22, 2013, 07:42 PM
American Eagle is made by Federal and most who reload, know that some Federal primers tend to be softer than other brands. AE brand is the budget brand and likely are made with lower priced components.
As others have mentioned, flattened primers do not always indicate high pressure, but if you add cratering around the firing pin, that could be an indication.


NCsmitty

rcmodel
November 22, 2013, 07:59 PM
but it's a heavy barrel, so I'm not worried about its ability to handle anything in the range of normal. Heavy barrel has nothing at all to do with the strength of a firearm, or handling high pressure loads.

The brass case is the weakest link in the whole chain.
It is the only seal between the chamber pressure and the inside of the action.

If the case lets go, the whole action will let go shortly after.
Like in a couple of milliseconds later.

Everything except the barrel that is.
Regardless of weight.

Blowing a rifle barrel or chamber is just not something that normally happens unless there is a defect in the metal.

And that is rarer then frog hair.

rc

Matno
November 22, 2013, 08:01 PM
Good to know. That's why I love this forum. It may save my face or life some day...

SlamFire1
November 22, 2013, 11:17 PM
The brass case is the weakest link in the whole chain.
It is the only seal between the chamber pressure and the inside of the action.

If the case lets go, the whole action will let go shortly after.
Like in a couple of milliseconds later.

Words of wisdom.

This shooter fired factory federal 223 and the case head blew. The shooter was protected by a combination of strong modern materials, good action design which protected the shooter from gas and debris. But, the bolt had to be replaced.

http://img.photobucket.com/albums/v479/SlamFire/Blowups/223%20Federal%20in%20CZ%20527%20bolt%20gun/IMG_1492FederalAmmunitionblowncasehead_zpse4e57169.jpg (http://smg.photobucket.com/user/SlamFire/media/Blowups/223%20Federal%20in%20CZ%20527%20bolt%20gun/IMG_1492FederalAmmunitionblowncasehead_zpse4e57169.jpg.html)


http://img.photobucket.com/albums/v479/SlamFire/Blowups/223%20Federal%20in%20CZ%20527%20bolt%20gun/DSC00893BlownCZ527brassinaction_zps8308cd72.jpg (http://smg.photobucket.com/user/SlamFire/media/Blowups/223%20Federal%20in%20CZ%20527%20bolt%20gun/DSC00893BlownCZ527brassinaction_zps8308cd72.jpg.html)

http://img.photobucket.com/albums/v479/SlamFire/Blowups/223%20Federal%20in%20CZ%20527%20bolt%20gun/IMG_1503CZ527blownextractor_zpsbe1b833d.jpg (http://smg.photobucket.com/user/SlamFire/media/Blowups/223%20Federal%20in%20CZ%20527%20bolt%20gun/IMG_1503CZ527blownextractor_zpsbe1b833d.jpg.html)

http://img.photobucket.com/albums/v479/SlamFire/Blowups/223%20Federal%20in%20CZ%20527%20bolt%20gun/DSC00886CZ527blownboltfaceandcollar_zpsa7486f6f.jpg (http://smg.photobucket.com/user/SlamFire/media/Blowups/223%20Federal%20in%20CZ%20527%20bolt%20gun/DSC00886CZ527blownboltfaceandcollar_zpsa7486f6f.jpg.html)

http://img.photobucket.com/albums/v479/SlamFire/Blowups/223%20Federal%20in%20CZ%20527%20bolt%20gun/DSC00882CZ527chippedboltface_zps9779ce5f.jpg (http://smg.photobucket.com/user/SlamFire/media/Blowups/223%20Federal%20in%20CZ%20527%20bolt%20gun/DSC00882CZ527chippedboltface_zps9779ce5f.jpg.html)

Actions are "strong" really in so far as they support the case, given that all modern actions are made of similiar alloy steels. Some actions support cases better and people who shoot over pressure loads are very lucky because their gun does not blow up as soon as would have happened if they had been using a "weaker" action.

Still, nothing made by man cannot be unmade by man:


http://img.photobucket.com/albums/v479/SlamFire/Blowups/M700%20blowups/P1010225_zps58c54456.jpg (http://smg.photobucket.com/user/SlamFire/media/Blowups/M700%20blowups/P1010225_zps58c54456.jpg.html)

http://img.photobucket.com/albums/v479/SlamFire/Blowups/M700%20blowups/Rem700300UltraMag3_zps68b79af9.jpg

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