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Okay...so we've established that 5.56X45mm and .223 are not identical. I may be a noob, but I've read enough to understand this.

My questions are as follows:

#1. My "read" is that most AR's are chambered for 5.56, not for .223. Correct?

#2. I've also read that the mil-spec 5.56mm chambers will digest .223 SAAMI spec rounds without problems. Correct?

#3. I'm switched on enough to have found the chart on ammo oracle detailing the specs for M193 vs. M855 regarding ranges and barrel lengths and fragmentation. Can anyone offer suggestions on how shooting frangible 55gr 5.56mm ammo will alter these fragmentation figures? How about 42gr frangible?

#4. Out of a short barreled AR with a 1:9 twist, is 55gr FMJ going to provide better lethality against zombies than a JHP in the 70gr range? Or should I go for a 50gr JHP?

Obviously I'll be sticking with plain old 55gr FMJ for target shooting based on the cost, but I'd at least like to know about what's going to work when the Zombies come.

I've tried to do my homework here (including looking at what's for sale at my local suppliers and favourite mail-order type places), but I would like to be sure bout these specifics.
 
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Okay...I'll just whip down to the basement and re-cut the rifling now.

Where can I pick up some mix for ballistic gelatin? And find a range that'll let me set up 12" x 12" X 24" blocks of solidified goo at the 15, 25, 50, 75, and 100 meter points?
 
From Armalites web site: Tech notes

P.O. Box 299 Geneseo IL 61254 Tel 309-944-6939 fax 309-944-6949 info@armalite.com
December 4, 2002
TECHNICAL NOTE 45: 5.56 NATO vs SAAMI .223 Remington Chambers
BACKGROUND: We are often asked whether our rifles feature NATO (North Atlantic Treaty Organization)
or SAAMI (Small Arms and Ammunition Manufacturers Institute) standard chambers, and whether it makes
any difference.
FACTS:
.223 Remington (SAAMI standard) and 5.56mm (NATO standard) rifle chambers are almost identical. The
difference is largely limited to the “freebore,” the cylindrical space in front of the case mouth, and the “lead” or
“leade,” the the tapered region that eases the bullet into full engagement with the rifling. NATO and SAAMI
cartridges can normally be used interchangeably with no problem.
The SAAMI chamber features less freebore and a tighter leade, which normally provide better bullet fit and
match-grade accuracy than the NATO chamber. It is wonderfully suited to match bullets.
Millions of rounds of NATO ammunition have been fired safely in Eagle Arms' and ArmaLite’s SAAMI
chambers over the past 15 years. Occasionally a non-standard round (of generally imported) ammunition will
fit too tightly in the leade, and resistance to early bullet movement can cause elevated chamber pressures.
These pressures are revealed by overly flattened or powder stains that reveal gasses leaking around the
primer.
The first few rounds of ALL ammunition, from whatever source or lot, should be checked for pressure and
other signs of defect before firing large quantities. If you have a problem, you can generally bet that the
ammunition meets neither SAAMI nor NATO specifications.
ArmaLite has adopted a practice of using a special, modified SAAMI chambers in its stainless steel match
barrels. This chamber is better for match use than the NATO chamber, but fires the NATO ammunition
perfectly. We use the NATO chamber in all moly (phosphated) and chrome-lined barrels.
ArmaLite’s larger AR-10 rifles are all chambered with 7.62mm NATO chambers. .308 Winchester (SAAMI
standard) ammunition functions perfectly in the 7.62mm chambers.
© 2001 ArmaLite, Inc."
 
There are also Wylde (sp?) chambers out there that are a retarded half hybrid of the two (NATO and SAAMI).
 
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