December 4, 2002
5.56 NATO vs SAAMI .223 REMINGTON CHAMBERS
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.
.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.
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®.