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5.56 and .223 mixed?

Mtn_Guy

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Both .223 and 5.56 feed/function fine when loaded as a mixed lot into a standard-capacity USGI pre-ban with a Magpul replaced follower. I’ve done this deliberately to see if I can “feel” the difference in the perceived recoil, as well as check for reliability Issues with the gun. On slow and deliberate single string of fire, I swear I can tell the difference. Had a buddy load several mixed mags and we’d take turns calling the caliber and then checking the brass. Could have been real good guessing, or maybe there was a perceived difference. On multi-shot groups, or engaging multiple targets neither of us could tell a difference. We weren’t checking casings either. I’ll also note, we were shooting 62 Gr 5.56 and 55 Gr .223.

Anyways, I generally shoot 55 Gr .223 for target and keep the 62 Gr penetrators for the zombie hoards.

I’ve noticed the real difference is in spread at 100 yds, where the lighter round will open up on pattern spacing. Realizing this, I focus more on aim small, miss small.
 

Tinkermatic

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As others have said, there are indeed slight differences in the chambers intended for the two rounds, namely the free bore length. If you test the cartridges themselves using the same methods, SAAMI (which the military does not) they’ll produce almost the same pressure of 55,000 psi. However, Because the free bore length of a .223 chamber is half that of a 5.56 (.0025 vs .0050 according to this guy) depending on the the actual bullets, you can end up with some varied chamber pressures that may not be healthy. This is from a reloading channel. He does a much better job than me and I’m just regurgitating his info anyway.
View: https://youtu.be/VCS4fXFmCyA
 

mothybee

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Same. I thought of this earlier because my eyes are getting pretty bad, need readers just to view this on my phone. If I had a 5.56 round and a .223 round in my hand, I can’t tell the difference by look or feel, and I can no longer read the small print on casings anymore. Just some boredom and “hey I never thought of this before” and “f*** I’m getting old”.
I'm in the same boat, good news is wait a minute and you'll forget what you were thinking about.
 

NavelOfficer

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FWIW, I'll throw in my 2¢...
Most load manuals don't differentiate between .223 Remington and 5.56x45mm. As mentioned in the video above, the newer Hornady manual does (Thrird Edition just lists .223 Remington). Most powder load data throws them together in one listing; I've only seen Alliant (Western Powders) give three distinct tables for load data for .223 Remington, 5.56 NATO and .223 Remington (Custom Long Throat).
 
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I'd like to see the actual data (observed peak pressure readings, moments of the distributions, and a Chi-square table) that shows commercially sold 5.56 is higher pressure than .223. Anyone know if this exists? Also, why do they treat pressure as if they're measuring a pipe-bomb instead of accelerating a projectile through a tube? It seems like the integral of pressure with respect to time would give a better description of a cartridge's pressure. Ultimately it doesn't matter because we know through trial and error what's safe, but I see a lot of pressure claims that don't seem to be backed up by anything. Just like every other gear-focused bro hobby.
 

mac1911

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To clarify, I know I can shoot .223 all day long in a 5.56, but directly having.223 and 5.56 in the same mag, is what raised my question. It’s my understanding that 5.56 has a thicker casing to protect it from burn off and being fired on burst or auto for extended periods, whereas .223 would allegedly cook off from the heat because it has a thinner casing. So would that thinner casing following a thicker casing cause a jam in the mag or misfeeds when chambering?
the 223/ 556 issue stems from the days when 223 rifles where designed around light varmint bullets where 55 grains where the heavy weights.
so what happened from what i understand is when 5.56 became available as surplus people where stuffing it in there weatherby 223 that had a short lead and slow twist barrels 1/12 - 1/14 as a 35-52 grain bullet was the norm.
So enter 5.56 ammo with 55-69 grain so now the bullet design is different and now the bullet being longer/fatter at the ogive can/will contact the lands of a bolt gun or 223 rem with a throat/lead cut shorter for the "lighter" bullets.
If you have a 223 with a 1/12 twist its a high chance it will problematic with 5.56 nato.
M16 have a generous lead/throat to be able to chamber the longest 5.56 including tracers and the faster 1/7 twist to stabilize those long tracers.

Some very early commercial ARs had 1\12 twist and could have problems with some bullet designs/weights/styles.
my buddies colt says 1/12 twist 223 on the barrel . Using wolf mil classic he pops primers we can assume tbe bullet is touching the lands enough to increase chamber pressure but not chambering problems.
He runs 52 grain ammo with no issues.

as fast as mixing ammo in a mag, unless your running extreme weight and velocity ranges you should be able to get hits on target with out messing with your sights with a 50 yard zero
 

mac1911

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I'd like to see the actual data (observed peak pressure readings, moments of the distributions, and a Chi-square table) that shows commercially sold 5.56 is higher pressure than .223. Anyone know if this exists? Also, why do they treat pressure as if they're measuring a pipe-bomb instead of accelerating a projectile through a tube? It seems like the integral of pressure with respect to time would give a better description of a cartridge's pressure. Ultimately it doesn't matter because we know through trial and error what's safe, but I see a lot of pressure claims that don't seem to be backed up by anything. Just like every other gear-focused bro hobby.
i think if you contact SAMMI they might have some of that info for you.
I know sammi pressure testing is down on specific equipment and its dedication to peak chamber pressure only.
 

mac1911

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FWIW, I'll throw in my 2¢...
Most load manuals don't differentiate between .223 Remington and 5.56x45mm. As mentioned in the video above, the newer Hornady manual does (Thrird Edition just lists .223 Remington). Most powder load data throws them together in one listing; I've only seen Alliant (Western Powders) give three distinct tables for load data for .223 Remington, 5.56 NATO and .223 Remington (Custom Long Throat).
I think you will see more info for sporting rifles or service rifles as the bullets are getting heavier.
Tell someone 30 years ago 80 gn bullets would be shot out of a 223 and they would ask why.
Also I think a majority of off the shelf 223/556 are cut with long leads like the 223 wylde to cover a larger variety of commercial ammo to cover the liability.
these is also why so many void warranty for reloads.

Be aware and when in doubt dont chamber it! Have fun
 
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I bet it would probably work without issue with any decent rifle. That being said I like to separate ammo by designation/brand just for ID purposes in case of a jam and because I'm anal like that.
 

NavelOfficer

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I'm not an AR guy, so how often do you normally use the forward assist ?
It's probably as common as slam fires with standard (non-milspec) primers, yes, no, other?
 

cams

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I'm not an AR guy, so how often do you normally use the forward assist ?
It's probably as common as slam fires with standard (non-milspec) primers, yes, no, other?

Everyone may have diff experiences with that but we were trained to always give it a good tap after racking the handle. Just became part of the charging process.
 

chris_1001

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I'm not an AR guy, so how often do you normally use the forward assist ?
It's probably as common as slam fires with standard (non-milspec) primers, yes, no, other?

Only have used it after a “press check” just to make sure the round is fully in battery as I don’t pull the charging lever any more than to see brass in the chamber.

Don’t think I’ve used it otherwise. But I prefer to have a FA vs not.
 

beaker

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The cases are identical, the SAMMI and Military spec's have different pressure specifications which makes 5.56 seem like it is spec'd to higher pressure, but the issue is that the two standards measure the pressure differently which is why the numbers are different. I have checked NATO brass and found it to be similar or less than 223 brass, with the exception of LC brass, which always seems to be a little bit thicker. 5.56 and 223 Rounds measured using the same pressure test method show them to be similar pressure. The big issue is the way 5.56 chambers are cut vs 223. the 5.56 chamber is slightly bigger, the lead geometry on a 5.56 chamber has more clearance around the case neck and out to the lands, which is why they say you can always shoot 223 in a 5.56 chambered barrel, but not the other way around. There is more room for case expansion in a 5.56 chamber, and it can accommodate longer bullets, so the high pressure situation is that in a tighter 223 chamber, shooting a 5.56 round with the bullet jammed into the lands, you could get a lot more pressure and have a kaboom. Most of the stuff on the internet regarding this is completely wrong.

Look at this site, I think this is the most accurate explanation I have come across.

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