Steve4102 said:
Not exactly correct.
The 223 Remington and the 5.56 NATO actually run at the same pressures.
The difference is in the pressure testing devices and how pressures are determined.
CIP places their pressure transducer further forward than SAAMI, as a result CIP (NATO) rounds will read higher pressure than SAAMI tested rounds.
Testing a CIP round and a SAAMI round in the same test barrel either CIP or SAAMI will result in identical pressures.
Our Moderator Unclenick has explained this to us many times. Maybe he can chime in and state these facts better that I.
That's one thing I tried to point out on another thread,
But I find "Steve's" conclusions incorrect based on the information printed by SAAMI.
5.56 NATO simply tries to push a heaver bullet faster, using higher pressure (presumably faster burn rate) propellant.
There is a difference in pressure ratings, CIP, CUP, PSI are often confused,
What I see published by the guys that have the proper testing equipment show higher pressures in 5.56 NATO rounds when adjusted for testing method and sample points in the case.
I simply don't have the testing equipment to verify everything published,
So I have to rely on the testing bodies for information.
(and not particularly what's published in magazines, since they are normally trying to interpret the actual testing data, mistakes can and are made)
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With bullet weights ranging from 30 grains to 99 grains, available to ANY RELOADER, experienced or not...
And considering the only way to increase mass (weight) of a bullet is to add length to the .224 diameter limitation,
The weight/length of the bullet issue alone makes me take pause.
To push the MASS of a 70 or 90 grain bullet at the same velocities as a 35 Grain bullet alone DEMANDS increased chamber pressures.
Properly accommodating the longer/heavier bullets DEMANDS changes in the freebore/throat of the rifle chamber, or you will effect case volume to accommodate the Cartridge Over All Length.
It's either case volume, pushing a long/heavy bullet back into the case and effecting the available case volume for propellant,
Or you lengthen the freebore/throat to accommodate the bullet.
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Then there is the question of cross sectional densities that have to be compressed into the rifling by the throat.
Longer/heavier bullets are simply harder to compress/form to the rifling, causing a pressure spike with any given amount of propellant.
It simply takes LONGER for the long heavy bullet to enter the rifling, driving up chamber pressures.
Another branch of that cross sectional density thing is composition of the bullet.
It's copper jacket, Lead Core, Steel Core, Steel jacket under the copper with a lead core?
A steel jacket is going to be harder to compress and take more time, driving up chamber pressures.
No 'Soft' lead (relative to steel) to compress along with the jacket as it enters rifling, so the copper jacket has to take on 100% of the deforming job to match the rifling.
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The next consideration is with rifling once the bullet makes it that far.
More turns of rifling in any given distance means the bullet takes longer to get out of that given distance.
To keep the same velocity, the pressure MUST increase with tighter rifling.
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I'm as curious as everyone else, I don't have all the answers, just some questions, and the warnings from SAAMI and some manufacturers of firearms & ammunition...
The second bullet point from
Federal Ammunition about shooting 5.56 NATO in .223 chambers...
Federal Ammunition is now owned by ATK, the same group that is running the Lake City Ammunition plant producing military ammunition.
This is the same group producing Federal Civilian & Law Enforcement Ammunition,
AND,
The military 5.56 NATO ammunition at Lake City.
Mil Spec 5.56 ammo typically has higher velocity and chamber pressure than the 223 Rem.
Link:
http://le.atk.com/downloads/technical_bulletins/223VS556.pdf
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The SAAMI "UNSAFE ARMS & AMMUNITION COMBINATIONS" Technical Data Sheet, Dated 31-Jan-1979,
(pretty well predates the 'Internet' comment earlier by about 2 decades)
SAAMI said:
The .223 Remington is rated for a Maximum of 50,000 CUP,
While the 5.56 is rated for a Maximum of 60,000 CUP,
The extra 10,000 CUP is likely sufficient to cause a failure in a chamber that's only rated for the 'Sporting' .223 Remington.
The same SAAMI technical data sheet warning goes on to state,
SAAMI said:
The .223 Remington and 5.56 NATO,
when checked with a chamber ream from a reliable manufacturer,
also have discernible differences in the area of freebore diameter, freebore length (leade), and angle of the throat.
The Throat and Leade I was aware of,
The Diameter of the freebore I was not aware of until reading this bulletin.
I've seen 5,000 PSI difference PRINTED,
I wasn't aware of the 10,000 CUP difference SAAMI saw in testing, since I always see the 5.56 rated in CIP and you have to do the conversion.
