November 07, 2011
The .223 (and its fraternal brother, the 5.56) do their terminal ballistic work in their full metal jacket guise by means of yaw and fragmentation. While efficient, it has its limitations. It is not easy to control the depth of the fragmentation process, and to make a bullet "weak" enough to fragment means it is not strong enough to penetrate. Also, the largest piece left, the flattened tip, doesn't track straight and doesn't weigh much.
Further, 55-grain full-metal-jacket ammunition, while it works exactly as it's supposed to on bare gelatin and light clothing, it fails on any intermediate barrier. Auto glass, window glass, sheet metal and wall board all cause the bullet to overturn, break apart and fail to generate sufficient penetration to do their job.
Ammunition makers have tried to solve these issues by bonding the core to the jacket, which keeps the bullet from breaking apart but also makes it expand like a deer bullet — and in the end making it less destructive than the fragmenting FMJ and also creating over-penetration problems.
Winchester has gone a different route with the .223 PDX1. The bullet is 60 grains, which is within the standard weight range and thus will work in all AR-15 barrel twist rates. Unlike the usual full-metal-jacket, though, the .223 PDX1 is an open-tip design.
The new design, called Split-Core Technology, uses two different alloys of lead. The front half of the core is made of a soft lead alloy and is intended to expand and fragment, producing the same wound as the full-metal-jacket. But that isn't all it does, as the harder rear half of the core doesn't fragment. The rear is a harder alloy and is bonded to the jacket — preventing it from separating from the gilding metal sheath it is in.
To test the ammunition, I selected a pair of rifles: One super-accurate LaRue Tactical OBR with a.223 Wylde chamber that handles 5.56 just fine and shoots .223 and 5.56 as if it were a benchrest rifle; and a converted M16A1 with a 16.5-inch barrel with 1:12 twist.
In the LaRue, the Winchester PDX1 bullet, which left the muzzle at 2,768 fps, shot at least as well as the bonded bullets offered as defensive ammo and better than many. While I can't really say it is sub-m.o.a. ammunition, it is clearly m.o.a. in accuracy — my accuracy test yielded a one-inch average at 100 yards — and certainly a lot more accurate than a lot of the .223/5.56 ammunition you could select for defensive use.
The 1:12 twist barrel of the M16A1 produced a velocity of 2,807 fps and did not show any signs of creating bullet instability. I can't say how accurate it really is because this rifle sports a carry handle, and since I learned long ago that mounting a scope atop the handle and trying to get good groups is a waste of time — so I shot it with iron sights. However, I got a 1.25-inch average with the irons at 50 yards; nothing wrong with that.
In photographing the test-firing, I noticed that I wasn't getting any images with muzzle flash. That's because Winchester uses the same powder in the .223 PDX1 that it uses for its FBI contract load: an efficient powder with a flash-suppressing additive.
As for performance, I visited Winchester and spoke to their designers, who showed me high-speed video of the bullet in gel tests. In the video, it is clear to see that while the bullet expands, fragments of it break off and create separate wound tracks, diverging from the initial impact line, just as the 55-grain full-metal-jacket load typically does. The harder-alloy base continues on in a straight line, delivering just a bit less than the one-foot minimum penetration that the FBI test protocols require.
Why fall short of the FBI requirements? Because if they set out to design a bullet to exceed that minimum, it wouldn't fragment and wouldn't create a wound track as large in diameter.
As do all compromises, the PDX1, at least in the .223, has to give up something in order to get something. For the 55-grain full-metal-jacket, the load gives up penetration for vigorous breakup and effect. If you are presented with an "open air" (no intervening barriers) shot, it will work quite well.
Counterintuitively, it also works well indoors, where the bullet rapidly breaks up on walls and other obstacles. The bonded bullets give up the rapid expansion/breakup in order to retain cohesion and permit penetration even after passing through intermediate obstacles. To do so, it has to forego the brisk fragmentation of the full-metal-jacket, with the added cost of over-penetration in some circumstances.
If, for example, you work around vehicles all day, you may want to be using a bonded bullet in your AR, as the full-metal-jacket loads will not do well on glass and sheet metal. However, the same bonded bullet will likely penetrate and exit any frame dwelling you happen to be in.
The Winchester .223 PDX1 offers some of each. In an open-air shot it will fragment while still penetrating to a useful extent. On an incidental barrier, it will penetrate the barrier while still retaining enough mass to penetrate the gelatin (or miscreant) behind.
It won't penetrate on sheet metal, wallboards and the like as well as a bonded bullet does, but it also won't over-penetrate on a frame dwelling to the extent the bonded bullets do. Wallboard barriers are not a big deal, as the PDX1 still produces 11 inches or so of gelatin penetration and 55 to 60 percent retained weight. Auto glass (which is a really difficult barrier for all bullets) shreds the front half of the core, and the rear then produces five to six inches of penetration, with about 40 percent retained weight.
So where does it fit? It's not a great long-range bullet because the 60-grain bullet doesn't have a terrific ballistic coefficient, and if it starts out at 2,750 fps at the muzzle, it'll drop 1.5 inches more than a 55-grain bullet at the same velocity. But at a typical defensive shooting range of 25 yards, that's not an issue.
It's not a varmint bullet either, nor is it a good choice if you need something that will drill through intervening barriers as if they weren't there. The bonded bullets offer much better penetration of chance obstacles than the 55-grain full-metal-jacket load does, but you do not always want that much penetration.
So where does this leave the Winchester PDX1? As a jack of all trades, the round offers you the most options, in the most situations, and does so without the sometimes severe shortcomings of the other loadings. As a general-purpose defensive loading in .223 — for a .223 Remington-chambered rifle in general and in particular an AR-15 — this is the load to have. If you know specifically what you'll need, ahead of time, then load up something else. But as the ammo to have in your magazines for general defensive, use this is the stuff to get.
The PDX1 is designed with a softer alloy up front, which fragments, ahead of a harder alloy core that's bonded to the jacket and provides penetration.
Caption 2: The PDX1 impacts a denim-covered gel block. In tests it penetrated just shy of the FBI one-foot minimum but won't over-penetrate wallboard, sheet metal and the like.
Caption 3: The front segment of the PDX1 fragments, creating myriad small wound tracks, while the harder rear core stays together and provides penetration.