Featured Proof’s CAMGAS Barrel System Iain Harrison January 25, 2017 A Cure for What Ails the AR-10 Photography by Straight 8 and White Cliff Productions Following the demise of the original AR-10 in 1960 and its subsequent runaway success when the design was reincarnated by Colt as the 5.56 AR-15, the first of Stoner’s direct impingement guns never got much in the way of development time and dollars, as compared to its little brother. When the great man joined Knights Armament in the early 1990s and resurrected the 7.62 gun as the SR-25, a highly refined logistics chain had already been in place for a quarter century. With so many spare parts already on the shelves, there was an assumption that whatever he came up with would use existing parts whenever possible. At the time, two gas system lengths were prevalent; the rifle-length one present on the M16A2, and the carbine-length version developed for the 10-inch barrel of the CAR15 carbine variants, subsequently used in the M4. It wasn’t until the 21st century that further refinement of the gas system led to the adoption of the mid-length and, more recently still, the intermediate-length gas system. Why should this matter? Well, your rifle’s gas system is the engine that drives its action and picking the wrong one is like throwing a 1.6-liter, four-banger under the hood of a Lambo, or shoehorning an LS1 into a Vespa. There are lots of variables to balance; moving the gas port closer to the chamber on a long-barreled gun provides not only much more pressure, but also increases the amount of time the system is pressurized, as it takes an additional few milliseconds for the bullet to reach the muzzle once it’s past the port. Greg Hamilton, a Weapons test specialist for Proof Research has 10-plus years in the firearms industry with some of the best and most recognizable names in the accuracy business. Conversely, drilling the gas port closer to the muzzle decreases the pressure it sees, as well as reducing the time under the pressure curve. Once you’ve arrived at the perfect combination of gas port diameter, and distance from the chamber (or dwell time) for one particular caliber, barrel length and ammunition type, expecting the same formula to work when you change all three variables is asking a lot. About five years ago, I built a 22-inch barreled .260 Rem AR-10, using the best technology available at the time, figuring that the combination of high ballistic coefficient bullets, low recoil impulse, and 21 rounds on tap would be the perfect solution to any long-range problem. Despite its adjustable gas system, the rifle cycled more violently than a comparable .308 gun and the telltale case head swipe on its ejected brass indicated the bolt was opening when there was still residual bore pressure. Resorting to the usual Band-Aid fixes of a heavier buffer and recoil spring reduced, but never eliminated the problem, so when Proof Research announced their Caliber Specific Gas System, or CAMGAS, I figured it was worth a look. Built on a Mega Arms .308 receiver set and equipped with Proof’s signature carbon-fiber-wrapped barrel, the test gun showed that unlike the AR-15, there’s been some significant improvements to the large frame platform in the past half decade. The most significant change Proof’s engineers made was to shift the gas port 2 inches closer to the target. By doing so, they took account of the slower burn rate of powders typically used in the .260 Rem, which generate peak pressures further down the bore and in a rifle-length gas system result in the problems I’d encountered previously. Further refinements can be found in the rifle’s Lantac Dragon muzzle brake and the same company’s enhanced bolt carrier group. The E-BCG is a work of art. Coated in proprietary UCT nickel boron, it gleams like the bumper on a ’56 Chevy and is slicker than snot on a Teflon doorknob. AR-10 bolts have traditionally been plagued with the twin problems of primer flow and slam fires, with the second of these addressed by the addition of a firing pin spring (itself cursed with a short service life). Lantac took a different approach, eliminating the spring, but lightening the pin by reducing its diameter at non-critical locations — pierced primers are a thing of the past due the smaller tip radius and correspondingly reduced hole in the bolt face. In order to compare the old and new guns head to head, comparable SIG Optics, variable first focal plane scopes were mounted up, and both varieties of magazines stuffed with PRIME 130-grain HPBT match ammo. After a couple of rounds to get on paper, both rifles were shot for groups at 100 yards and the old AR-10 turned in a respectable average group size of 0.65 inch, measured with calipers. The Proof Research gun shot 0.50-inch groups repeatedly, which is remarkable consistency for factory ammunition. The biggest difference between the two rifles, however, was in terms of their ability to stay on target throughout the string. The AR-10 bucked and shuffled, while the Proof/Mega combo recoiled straight back. At longer ranges, the ease with which it was possible to spot strikes through the scope meant for instant corrections in case of a miss, and a second round was on its way as soon as the trigger could be reset. It’s not until you shoot both guns side by side that the difference becomes acutely noticeable and anyone who shot them at our range session left with a distinct preference for the carbon-fiber- barreled gun. It would seem then, that the combination of components selected for the Proof Research .260 Rem work symbiotically in a way my old AR-10 couldn’t manage. The use of a longer gas system in particular solves the biggest headaches of timing the carrier group and turns the large frame rifle into a vary controllable tack driver, able to make use full use of the 6.5mm diameter bullet’s ballistics. Proof Research CAMGAS Barrel System Caliber: .260 Rem Barrel: 22 inches Twist: 1:8 Rifling: 4-groove cut Weight: 2.8 lbs CF 3.6 lbs SS MSRP: $940 URL: www.proofresearch.com Complete Rifle as Shown: $3,183 Featuring: Mega Arms MATEN Receiver Set: $900 Lantac E-BCG Heavy: $345 Lantac Dragon Brake: $160 Magpul PRS GEN3 Precision-Adjustable Stock: $255 Explore RECOILweb:Dueling Tree Target Stands From Birchwood CaseyPreview - Latest In Collapsible ButtstocksHow to Pepper SprayChasing Muzzle Velocity Standard Deviation and Extreme Spread for Precision Rifle Shooting NEXT STEP: Download Your Free Target Pack from RECOILFor years, RECOIL magazine has treated its readers to a full-size (sometimes full color!) shooting target tucked into each big issue. 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