We've been looking forward to testing TacomHQ's Structured barrel for some time now and finally got our hands on one. Imagine a barrel that shoots as good as a 1.6" straight contour heavy benchrest barrel but weighs less that an M40 and much less than an MTU contour. For you handloaders out there imagine a barrel that shoots each load as well as the last. In essence, that's what TacomHQ has done.
For those of you not familiar with the concept here's a brief explanation from the horse's mouth..... (skip to 2:10)
Though the Structured Barrel design shines in larger calibers we wanted to test something smaller. While the 6mm Creemoor is the latest preferred caliber in PRS and similar competitions, it struggles with barrel heat and throat erosion like all the overbore cartridges. We wanted to test the effect on barrel life, as well as the cooling properties of the design.
The main claim of the manufacturer is that the structure of this barrel design works with physics to gain the rigidity of a massive barrel without the weight. By drilling a multitude of bore-holes around the center of the barrel three things are accomplished. First, a drastic reduction in weight. Second, an impressive increase in surface area to aid in cooling. Third, an increase in rigidity. This last claim might seem counter-intuitive but it is true. The strength-to-weight ratio of this 1.6" barrel is much higher that a similarly sized non-structured barrel.
Time to get nerdy. When you fire a normal rifle barrel, especially one on the lighter side, the barrel vibrates or flexes. It's easiest to think of this as occurring in two dimensions, up and down, though a barrel can flex in any direction. One way shooters overcome this detriment to accuracy is by shooting heavier barrels. While this factor alone increases accuracy it comes with a obvious cost. Anyone who has carried an MTU barreled rifle knows how unpleasant these are to carry. Also, these heavy barrels can make a rifle very front heavy and harder to shoot. The muzzle velocity of a load fired through this barrel will exit at a certain point in this flex. The more flex, the harder it may be to find an accurate load.
Essentially, what we try to accomplish when finding a perfect load for a customer's rifle is to locate the top or bottom of this flex. Just as a ball thrown upward has its least velocity when it stops to begin its descent, so it is with the barrel of a rifle. By finding this slow point, or harmonic node, we can decrease our group size by reducing the angular effect of the velocity variations inherent in every load. Put differently, the group size of a load with an SD of 10 fps that is near this "node" would likely be smaller than the group size of a load with an SD of 8 fps that is not near the "node". The latter load's velocity variations would be more obvious on the target as the velocity of the barrel's muzzle, transferred to the projectile, would lead to greater dispersion down range. (If you'd really like to geek out on these concepts, visit Varmint Al's Website. But don't stay on his website for too long. You'll go mad! (GIF Credit to Varmint Al)
The design of TacomHQ's Structured Barrel attempts to mitigate this harmonic flexing by using the same principle as a structural I-beam. When under load, the top plate of the beam is in compression and the bottom is in tension.
With holes drilled around the bore of the barrel, when one hole experience compression, a hole on the other side of the barrel experiences tension. The forces counteract and result in a muzzle straying less from its original/natural point of aim.
To attempt to observe this phenomenon we performed a crude ladder test at 100 and 400 yards. We started at a very low charge of RL 16 and increase each shot by 1/2 grain increments. The idea was to try to detect the harmonics of the barrel in the resulting group size. (Factory ammo, along with high quality handloads, had already been tested in this barrel, all with POI deviations from each other being less than 1/2 MOA at 500 yards.)
The velocities of this ladder test can be observed at the end of the video above. The extreme spread was 125 fps and the resulting group was 0.49 MOA (mostly horizontal). The shot low was the fault of the shooter. He's not perfect. We performed similar testing with different ammo and saw the same result.
This was by no means a definitive result. So we tried the same ladder test at 400 yards. Interestingly, the same 1/2 MOA horizontal dispersion was observed, but now the the vertical dispersion followed as the velocities would predict.
Conclusion: This barrel is more harmonically quiet to a degree one would be unlikely to see from a barrel of similar weight. More testing will be needed but we are satisfied that TacomHQ is on to something here. So satisfied that we ordered a 375 Cheytac barrel from them to go on a Stiller 408 single shot action. Look for that and more videos and articles to come.