Thoughts on selecting .223/5.56MM ammo

My primary defensive carbine is a Colt AR-15A3 Tactical chambered for 5.56MM NATO. This rifle has a barrel length of 16 inches and a twist rate of one turn in nine inches (sometimes designated 1:9 or 1/9). I've done a fiar amount of online research into what sort of ammunition I should use. Two primary sources for info are the Ammo Oracle and the Arfcom AR-15 Ammo Forum.

Based on these sources it appears that the heavy bullet loads at 5.56MM pressures (see the Oracle for the difference between .223 and 5.56MM specs) are the most effective, because they fragment the most reliably. They are also the most expensive, and I like to practice with something more equivalent to my defense load.

Aside from wanting to practice with the same or similar load as to that which I'd rely on for defense, I have to take into account the 1:9 twist of my Colt. The heaviest loads require a 1:7 twist to stabilize. A 1:9 may be able to stabilize bullets up to about 69 grains but beyond that it's doubtful.

I'm avoiding M-855 spec ammo (62 grain with steel penetrator) because (a) it does not fragment as reliably as M-193, and (b) it's more expensive. If I thought that I'd need the extra penetration then I'd buy some, but absent a Hurrican Katrina type SHTF event, I don't.

So, my primary pick is Federal Lake City XM-193 of which I've laid in a stash. Future availability of this load appears to be questionable, however. So, for practice purposes I have Federal American Eagle .223. This is about 100 FPS slower than M-193 spec ammo but for practice out to 100 yards it's not significant, and my Colt runs good with it.

I'm not an ammo snob and if Wolf .223 ran well in the Colt I'd use it for practice. Many people have had good luck with Wolf in their ARs, however I am not one of them. When I tried it I got several bolt over base failures to feed. I do have about half a case left and it runs well in my Mini-14, so that's the gun in which I'll use it up. Note that I do not recommend Wolf for defensive use, because the bullet jackets are thick and the FMJs don't fragment, while JHP fragmentation is uncertain.

Winchester's Q3131 and Q3131A loads are essentially identical to Federal XM-193 and should be interchangeable from an end user's point of view. They may be more available than the Federal in the future.

Federal has posted the results of gelatin tests of several different .223/5.56MM loads on their website, here (PDF file). What I found interesting about the gelatin results is that although the 55 grain American Eagle load has a longer "neck" on the permanent cavity, overall disruption appears to be roughly equivalent to the fancier "tactical" loads. So, if true M-193 spec ammo availability dries up in the future, the AE .223 55 grain FMJBT loads look like a good substitute for civilian defensive use.

The good news with respect to M-193 spec ammo is that a batch of Guatemalan surplus M-193 just hit the US; AIM Surplus has it. Also, Wolf is now importing M-193 made by Prvi Partizan in Serbia. PP ammo was imported into the US under the Hansen name back in the 1980s before the whole Balkan shitstorm of the '90s, and was very good. I shot up a bunch of it in .303 British and 6.5x55 Swedish. So, I am optimistic that the Wolf Gold M-193 will be good as well. Along with a friend I'm planning to go to the Valley Forge Gun Show on March 12th, and hope to pick up a few boxes to try out. If it shoots as well as I hope, I plan to add more to my stash.