[Ed Warden]

Good morning all, I just purchased a Remington model 700 varmit rifle with a heavy barrel can someone tell me if this rifle which is a .223 can shoot a 5.56 nato round, i have heard that there is a slight difference in rounds but in the new rifles does it really matter which round you shoot, and what is the best way to breakin the barrel or do you have to break it in.Thanks, Ed

[dnthmn2004]

While the external case dimensions are very similar, the .223 Remington and 5.56x45mm differ in both maximum pressure and chamber shape. The maximum and mean pressures for some varieties of the 5.56 mm (different cartridge designations have different standards) exceed the SAAMI maximums for the .223 Remington, and the methods for measuring pressures differ between NATO and SAAMI.[2] The 5.56 mm chamber specification has also changed over time since its adoption, as the current military loading (NATO SS-109 or US M855) uses longer, heavier bullets than the original loading did. This has resulted in a lengthening of the throat in the 5.56 mm chamber. Thus, while .223 Remington ammunition can be safely fired in a 5.56 mm chambered gun, firing 5.56 mm ammunition in a .223 Remington chamber may produce pressures in excess of even the 5.56 mm specifications due to the shorter throat.

So you can shoot both .223 and 5.56 in a rifle chambered for 5.56. You SHOULD only shoot .223 in a rifle chambered for .223.

As for breaking in a barrel; shoot once, clean, repeat 5ish times, shoot two, clean, repeat5ish times, etc up to about ten rounds. I'm not an expert, but this sounds right, guys?

[Dillinger]

That about sums it up.

Your rifle is stock, I take it? Like just out of the box? You didn't have it built for you from a gunsmith?

If your chamber was cut for .223 - your accuracy will suffer with 5.56mm Nato stuff, and the pressure COULD BE enough to cause damage to the weapon.

If your rifle was cut with a 5.56mm chamber, you can safely shoot the .223 stuff from a pressure stand-point, but again, your accuracy will suffer.

JD

[bgeddes]

I'm sure Remington knows, you should ask them. My guess is it will not be a problem. Have fun with your new rifle.