Thread: 5.56mm vs .223 cal chambers

Originally Posted by gunmaker

Since there is a growing interest in rifles which are marketed as 'military type' rifles. I thought a bit of advice on cartridges for those rifles is in order.
If you have purchased a rifle chambered for the 5.56 or .223 cal. ammo, take note, they are NOT in all cases interchangeable.
Rifles designated to shoot ammo in the 5.56 military chamber can safely shoot the 5.56 ammo and the .223 ammo interchangeably.
Rifles designated with the .223 caliber chamber should only be used with .223 ammo.
The .223 chamber and the 5.56 chamber are nearly identical, but NOT enough to allow the SAFE function interchangeably. The use of 5.56 cartridges in a .223 chamber can result in an over-pressure situation, with results that can be dangerous!
Please know your weapon and ammo, and practice firearm safety!

Hopefully, the old Dougster™ is in good shape (i.e., "safe") in that regard...

My Bushmaster: Bushmaster - Home Defense & Recreation Rifles

...but could you speak to the issue of 5.56mm "XM" ammo (and more specifically Federal's "American Eagle" XM193 ammo)? Do you consider it safe to use in my Bushmaster? This is one of the precious few bulk purchase 5.56 ammos that are available to me on a regular basis. It is regularly stocked by one dealer in Southern NH... so I don't have to wait for a "show" to buy it. However, the XM designation is giving me pause. Some seem to think it's alright... others not so much. I'd appreciate your thoughts.

Dougster™

p.s., Remember that mail order sales are effectively banned in MA for all intents and purposes thanks to our wonderful "moonbat" AG. -d

Originally Posted by gunmaker

If you look at the left side of your mag well, near the Bushmaster logo, you will most likely see '5.56'. That is the chamber designation, and your can use both 5.56mm and .223 cal ammo.
Federal is the manufacturer of 'American Eagle' ammo, and the XM193 and AE .223 are just different names for a very similar product. The "XM193 is said to be 5.56mm loaded to NATO mil-spec.
Remington markets a UMC .223 round that's as cost effective as the Federal, and the Winchester Q3131 ammo. I have found the UMC and Federal to be a bit more accurate than the Winchester. Having said that, you need to find what your rifle shoots best.
All good plinking ammo.

Federal AE specs:
Federal Premium - Rifle Details

Thanks GM... but I'm going to press you a little harder on that "XM" ammo issue if you don't mind.

Depending on who you talk with or what you read, the designation "XM" can mean either:

1) Military contract overrun ammo, or
2) Military reject ammo (i.e., "did not meet all mil-spec requirements for M193"), or
3) Military "for training use only" ammo.

For whatever reason, it can't be called M193. Pix of typical boxes are below (note that this is not American Eagle red box). If I understand correctly, most or all of this XM ammo is actually made by Lake City and merely sold through Federal distributors and dealers.

Some folks say it is perfectly fine for non-combat use and pay no attention to the XM designation. Other folks say that it does not meet all mil-spec requirements and that should be a red flag. In particular, some feel that they might be undercharged or overcharged. Field reports are all over the place. Some do fine with it, others not. Some even believe it is not safe to store longterm or to use in extreme hot weather.

Again, the reason this matters so much to me is that it is one of the very few ammos that I can buy locally (Southern NH) in bulk and at low bulk prices. My only other alternative in 5.56 is Prvi M193 (great stuff supposedly, but not made in USA and only available in bulk at certain shows.

As a side note, I'm up to my eyeballs in UMC, but most folks report it to be a dirty burning ammo. I guess I will find out soon enough. But in regard to Winchester Q3131 ammo, it's priced way beyond my budget.


Dougster™

XM is the military designation of Experimental Model...i.e. not standard at this time...

The Gun Zone -- A 5.56 X 45mm "Timeline" Prologue