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Old 03-04-2013, 01:03 AM   #21
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Old 03-04-2013, 02:26 AM   #22
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So even if the ammo is exactly the same in some cases, or if you have high power / military 556, it seems that a large difference is in the chambering of the rifle itself. Very interesting. Thanks for that detailed pic. I would imagine that in the case of this case, because of the small differences in the gun itself, once fired brass must be much more accurate.
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Old 03-04-2013, 03:34 AM   #23
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Do you realize how much easier life would be for us reloaders if chambers were actually cut to spec? One magic length would work in any rifle......ahhhhh That is a fantasy land. In the real world I just bought a new Browning so inaccurate you could aim straight down at the ground and miss, even with my best match handloads and a stable rest. You think that rifle has it's chamber properly cut to spec? No the real reason you cannot shoot 5.56 through a 223 is pressures period, the cartridges have the exact same external dimensions and there is no way you could design a throat to work with one and not the other except for pressure.

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Old 03-04-2013, 05:27 AM   #24
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Do you realize how much easier life would be for us reloaders if chambers were actually cut to spec? One magic length would work in any rifle......ahhhhh That is a fantasy land. In the real world I just bought a new Browning so inaccurate you could aim straight down at the ground and miss, even with my best match handloads and a stable rest. You think that rifle has it's chamber properly cut to spec? No the real reason you cannot shoot 5.56 through a 223 is pressures period, the cartridges have the exact same external dimensions and there is no way you could design a throat to work with one and not the other except for pressure.
The case dimensions are identical. The design pressures appear to be close enough that they dont concern me greatly.

What does concern me is: The 5.56 NATO chamber has a longer leade, than the 223.

The shorter leade on the 223, means that rounds loaded for the 5.56 with bullets seated further out to match that chamber, will be touching the lands, and may develop extremely high pressures.

My brother and I both own 257AIs. Mine has a longer leade than his, and the rounds I load to be 0.004 off the lands are actually pushed into the lands on his, resulting in high pressures if he fires my loads in his rifle.

So, even small differences in chamber/barrel geometry can make a major difference in pressures.

I think that if I owned a 223, I'd be very tempted to have the chamber reamed to the NATO 5.56 chamber. It would still handle 223 rounds, but would eliminate the potential for high pressures from the 5.56.
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Old 03-04-2013, 06:05 AM   #25
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Yes but then you risk too much jump on the lands and your accuracy goes to $#!^ especially with the common base heavy boat tails. There are rifles in short throat and long throat in every caliber and the 223 is no exception, some calibers namely the 240 Wbys are bad about excessively long throats. You are right it does take the edge off the pressure just a bit, but too much jump is always a bad thing.

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Old 03-04-2013, 08:20 PM   #26
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I'm guessing here but I think that at some point in time some gun writer fired hand loads for a 5.56 with the bullet seated out, in a .223 and had pressure issues. That individual then write about it. In the intervening years it has spread and become gospel, parroted onward with out thought or reason until now it's just one of those everybody knows things like the increased velocity in Ackley Improved rounds is because of larger case capacity, and case efficiency. Mostly it was because he increased the pressure about twenty percent, and blew out the shoulder so you couldn't chamber the round in a rifle that hadn't been reworked.

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