Is there a real difference between 55gr XM193 and let's say, some WalMart valuepack WWB 55gr ammo? I know XM193 is milspec, but what does that mean, precisely in terms of quality? Why is XM193 FMJ 55gr round more desireable than something like 55gr. Winchester WB ammo?

I have heard that the milspec stuff is more consistently loaded. Has anyone done a chrony test of the two (or three with Q3131A) rounds?

How about bullet construction? Does XM193 or Q3131A have a better bullet than WWB?

Thanks for indulging my curiosity.

The M193 round was the original ammo designed for use in the M16A1 during the VietNam era. The 1x12 barrel twist in the A1 kept the bullet right at the edge of instability so that it could do maximum damage on the target by yawing/tumbling on impact and fragmenting, and the spec on the bullet construction (balance, brass thickness and hardness rating, etc) was intended to ensure that result. Since it is a military round, it is purposefully designed to kill human targets.

M193 fragmentation only occurs within a limited range of velocity, and I believe tests show it will not occur below 2,700 fps. That equates to a max frag range of about 125 yards out of a 20" barrel (see the Fragmentation pinned post). Granted that is close range, but then remember VN was a close-range war.

US commercial ammo follows SAAMI specs for muzzle velocity, which for 55 gr FMJ .223 ammo is generally about 200 fps slower than M193. SAAMI FMJ rounds are designed for general purpose shooting at minimum cost, and in the defensive spirit of Political Correctness it is neither designed nor marketed for "killing" purposes.  Couple lower velocity with perhaps a thicker/harder brass jacket on the bullet designed to reduce production cost and you have reduced the factors which will ensure yawing/tumbling and fragmentation. And unless you do extensive testing of any SAAMI round on your own, you will have no idea what its terminal characteristics are going to be, whereas any round which meets the M193 milspec will, by presumption, give you the result the M193 was designed for.

So if you are considering SHTF, you want ammo which maximizes the probability that it will have maximum damage impact on the target, and unless you are into Tactical/LEO type ammo and your barrel has the twist rate to handle it , M193 is that choice.

Quoted: The M193 round was the original ammo designed for use in the M16A1 during the VietNam era. The 1x12 barrel twist in the A1 kept the bullet right at the edge of instability so that it could do maximum damage on the target by yawing/tumbling on impact and fragmenting, and the spec on the bullet construction (balance, brass thickness and hardness rating, etc) was intended to ensure that result. Since it is a military round, it is purposefully designed to kill human targets. M193 fragmentation only occurs within a limited range of velocity, and I believe tests show it will not occur below 2,700 fps. That equates to a max frag range of about 125 yards out of a 20" barrel (see the Fragmentation pinned post). Granted that is close range, but then remember VN was a close-range war. US commercial ammo follows SAAMI specs for muzzle velocity, which for 55 gr FMJ .223 ammo is generally about 200 fps slower than M193. SAAMI FMJ rounds are designed for general purpose shooting at minimum cost, and in the defensive spirit of Political Correctness it is neither designed nor marketed for "killing" purposes.  Couple lower velocity with perhaps a thicker/harder brass jacket on the bullet designed to reduce production cost and you have reduced the factors which will ensure yawing/tumbling and fragmentation. And unless you do extensive testing of any SAAMI round on your own, you will have no idea what its terminal characteristics are going to be, whereas any round which meets the M193 milspec will, by presumption, give you the result the M193 was designed for. So if you are considering SHTF, you want ammo which maximizes the probability that it will have maximum damage impact on the target, and unless you are into Tactical/LEO type ammo and your barrel has the twist rate to handle it , M193 is that choice.

 Great, thorough response, Joe.  Always nice to see someone take the time to be so helpful.  One question, if the 1 in 12 twist kept the bullet that close to instability, shouldn't the 1x7 break it up?

I'm not sure if a 1x7 would break it up, perhaps if the bullet were defective it certainly might.

What's more the issue with spinning the bullet too fast is that too much of the force imparted to it by the propellent goes to spin and that reduces the force applied to forward motion. That bullet may have the tendency to "nose up" and lose accuracy, distance and impact effect.

Think of what a football does if you spin it too slow compared to its forward speed. It will seem to have good forward motion initially but eventually its wobble will slow it down because of friction with the air. Yet if you try like hell to spin it, less of the strength in your arm will go to forward motion and she is likely to wormhole almost from the beginning of its flight.

Everything is a balance.

Supply/Ordnance was what I did in Uncle Sam's Army back in the early 70s, and we spent a lot of time learning about the care and feeding of the M16A1 and its ammo.

The twist rate has NOTHING to do with wounding.  Otherwise, mostly accurate information.  

The M193 WILL shoot just fine out of a 1/7.  I've shot it out of 1/7 twist M16s and it does fine.

Well to be precise, twist HAS to do with wounding. BUT it is a factor which is probably not measurable relative to all the other factors going in, like bullet and powder tolerances and the like.
55gr is not overstabilized out of a 1:7., it will follow the flightpath just fine.

Consider the fact that the very first twist rate for the M16 was 1x14.

Field test reports were that it created terrible wounds. Only one problem: you got about one-minute-of-barn-door accuracy with it.

If you can't hit 'em, you can't kill 'em.

As I said, everything is a balance.

Yes, but still, as far as I know and recall a 55gr out of a 1:7 wont (measurably) do less damage. Muscle tissue is  about two orders of magnitude denser than air, so if stabilized in air doesnt mean its stabilized in flesh at all, the difference is just too big. Did a thumb calc once, the twist needed to stabilize a bullet in flesh would need a twist about as steep as a regular screw-thread. As this is obviously not the case, the bullet with its (for flesh) low spin wont notice the difference. It will still yaw and fragment, given the right parameters as speed and bullet design.

And yes the twist was steepened to 12" as the bullets became unstable in cold air. Still I know of no accounts where this had detrimental effects on the wounding capabilities, but I am willing to learn .

Regards!

[edit] Three orders of magnitude.