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2 dumb questions

 
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  #1  
Old 02-04-2012, 07:52 PM
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2 dumb questions

I have an FNar that reads 7.62x51
I have another Ar-15 that reads 5.56x45

Question; assuming the answer is the same for both these examples.

I can shoot 7.62x51 or 308 in my gun because it can handle the higher pressure of the 7.62x51 and the same for my 5.56x45 use 223 too?

I haven't gone down to look but I am just getting into reloading, can I use either case to reload or do I have to be specific? If specific, which cases should I choose.

I have other 308's so until I start reloading, and I know that fire forming in the chamber locks in the 308 loads but how about my AR's as I have used both.

Thanks
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  #2  
Old 02-04-2012, 08:39 PM
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Re: 2 dumb questions

I am not sure about the 7.62.

My father has a DPMS 5.56 and he shoots pretty hot loads out of it. To my knowledge there is no difference in the brass for the 5.56 or 223. I have been told not to shoot 5.56 out of .223 But there are some loads for the .223 that are higher pressure than a 5.56. They also use the same dies.

As always with reloading take baby steps and work you way up. The golden rule is take the recomended load and drop it 10% then work up from there.

Also try the Horniday 69gn (I think that is what they are i know they are 69gn) and use Varget. Most accurate load we have found (Using CCI SR primers).
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  #3  
Old 02-05-2012, 12:53 PM
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Re: 2 dumb questions

Quote:
Originally Posted by etisll40 View Post
I have an FNar that reads 7.62x51
I have another Ar-15 that reads 5.56x45

Question; assuming the answer is the same for both these examples.

I can shoot 7.62x51 or 308 in my gun because it can handle the higher pressure of the 7.62x51 and the same for my 5.56x45 use 223 too?
Thanks
It's a popular myth that the military 7.62x51mm cartridge has unsafe higher pressure than the commercial .308 Winchester. The reason is that some specs are listed in the old copper units of pressure (CUP) and other specs in modern piezoelectric strain gages' pounds per square inch (PSI) . 52,000 CUP has virtually the exact same pressure as 61,000 PSI. The conversion's not exact but this is within 1%.

Worse yet, is the fact that some places (web pages, manuals, word of mouth, etc) state pressure in PSI when the value is really CUP. The reverse happens too. Best examples are in older books published before piezoelectric strain gages were invented. Peak pressure valuse are often listed in PSI when the only methos used to measure peak pressure was copper disks crushed in a special pressure test gun.

Both the commercial and military versions of each cartridge have virtually the same peak pressure specs. The difference between them is less than the difference between maximum average and maximum peak pressures. Check out SAAMI's web site and look at your favorite cartridge maximum average pressure in one of the documents listed under "SAAMI/ANSI Standards:"

http://www.saami.org/specifications_....cfm?page=ANSI

Google for "MIL-C- 7.62" then pick one of the military specs for the 7.62 NATO round for its peak pressure. Virtually all are listed in PSI but were actually measured with CUP numbers.
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  #4  
Old 02-05-2012, 01:21 PM
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Re: 2 dumb questions

You do not shoot bolt gun .308/7.62 loads in a gas gun. As stated .308 and 7.62 are
the same. 5.56 and .223 are not. The shorter tighter throat on a .223 can pinch the
bullet as the brass stretches into the throat. I don't think it has ever been a problem in
a bolt gun but it has been in an AR.
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  #5  
Old 02-05-2012, 01:25 PM
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Re: 2 dumb questions

I stand corrected. There must be a slight difference because eyeball a 556 and 223 and i cant tell the difference. Ill mic the cases sometime.
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  #6  
Old 02-05-2012, 02:04 PM
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Re: 2 dumb questions

Both are interchangeable with the exception of an AR with a basic saami 223 chamber where there is almost no freebore/short throated and a steep leade angle then you will have brass flow issues as mentioned earlier. The dimensions, case wise of the 7.62 and 5.56 are the same externally but the millitary brass typically has less internal capacity. There are several variations in 7.62 and 5.56s in AR platforms, but the differences are all simply throat length and design. But for your ARs I reccomend using a full length small base circle die to reload for them for consistency and feeding reliability, and I use the neck sizing method for bolt guns.
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  #7  
Old 02-05-2012, 02:09 PM
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Re: 2 dumb questions

I do not shoot 7.62 but on the 223 the ar will only feed correctly if i use a Small Base die. I use Neck Dies for all of my bolt guns as well but for my fathers AR it is a Small Base (Full Length Would also cause problems). Im starting to miss that little thing, was a fun plinker.
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