The AR-10 was designed to handle the 7.62×51/.308 Winchester and other .308 “family” cartridges such as the .243 Win and .260 Remington. Our friend Dennis Santiago recently put together an AR-10 to shoot the accurate .260 Rem cartridge. Here is his initial report:
AR-10 Platform Chambered for .260 Remingtonby Dennis Santiago
I was very curious to see how the .260 works in the AR-10 compared to a .308. I’ve always thought about chambering a bolt gun in .260 but before doing so I thought it’d be good to try it using a less expensive entry point. With an AR platform’s easy interchanging of barrels, it seem like the best way to test out the .260 Rem chambering. So far, it’s most impressive.
DPMS LR-308 in .260 Remington getting function cycle tuned and zeroed
I took the AR-10-type .260 Rem a step closer to being ready for matches yesterday. The first order of business was to confirm which buffer spring to use with both the 123 grain and 140 grain bullet loads. My .260 Rem loads, on average, are using 4-5 grains less powder than the .308 loads. In a semi-automatic action that means less gas/energy to work the mechanics. The solution in an AR-10 platform is to either cut coils in the .308 spring or use a weaker AR-15 buffer spring; yup they are not the same. In this case, a CS flat spring for the AR-15 did the trick.
I also put a very nice NightForce Benchrest 12-42x56mm scope that came via friend Mark Gravitt on it and got zeros. This scope’s 1/8th MOA clicks are nice. The AR-10 had previously mounted a NightForce F1, a more “field tactical” 3-15X system. This 12-42X scope now sets this gun up as more of a target cannon. Field of view is limited when your minimum magnification is twelve. Maybe I’ll put an auxiliary red dot on it just to find the target.
Pet Loads: H4350 and Lapua 123gr Scenars Comment by Daily Bulletin Editor
Over a two-year period, this Editor put a lot of rounds through a .260 Remington. I did a ton of load testing with that Savage-actioned rifle (before it was rebarreled as a 6mmBR Norma). I tried two dozen load recipes with five different powders and bullets ranging from 100 grains to 142 grains. Hodgdon H4350 was my “go-to” powder. As many 260 Rem shooters have discovered, H4350 is a winner in the .260 Rem. This propellant delivered the lowest ES in my rifle and nothing beat H4350 for consistent accuracy with bullets in the 120-140 grain range. My most accurate load was with Lapua 123gr Scenars, pushed by H4350 and CCI 250 primers. The 123gr Scenars worked well jumped as well as seated into the lands. Best accuracy, in my 24″-barreled .260 Rem, was right about 2950 fps. Other powders work well, but H4350 is a very good choice for the .260 Remington (as well as the smaller 6.5×47 Lapua cartridge).
For many cartridge types, Hornady Superformance ammunition provides enhanced velocity compared to some other types of factory-loaded ammo. However, Hornady has found that there may be issues when Superformance ammo is shot in gas-operated guns with barrels under 20″, or with barrels fitted with suppressors. This is because the gas returning from the barrel port may cause the bolt to begin unlocking prematurely. Hornady has published the following information concerning the uses of Superformance ammo in direct impingment and gas piston self-loading rifles.
Internal Ballistics of Superformance Ammo in Semi-Auto Guns
Superformance™ ammunition is tested and is safely within SAAMI pressure guidelines. Gas operated (direct impingement or gas piston) firearms are perfectly safe to use with Superformance ammunition. However, Hornady ballisticians have conducted testing with a variety of guns (including guns equipped with suppressors), and our findings conclude that some systems work far better with Superformance ammunition than others.
It is recommended that to get the best functioning with Superformance ammunition in gas operated/gas piston semi-automatic or select fire guns, rifle length gas systems with 20 inch or longer barrel lengths are best for reliable firing and extraction. Any other configuration — particularly shorter barrels/gas systems — are best served with the installation of an adjustable gas system, ESPECIALLY if a suppressor is to be installed.
Due to the longer duration of peak pressure produced by Superformance, the post peak/declining port pressure at common carbine and mid-length gas port locations is still higher than that produced by standard propellant. This has a tendency to flood the system with a larger volume of gas, at a higher velocity, that tries to open the bolt of the gun too fast. It’s a timing issue. The cartridge case is still swollen from the application of pressure during firing while the gun is simultaneously trying to extract the cartridge case before it has had an opportunity to settle back to its original size, or more simply: the gun is still in the process or firing while it’s trying to extract the cartridge case.
If the firearm and the ammunition are not in sync, there can be what is commonly identified as “pressure signs” on the cartridge case. This is exhibited by the movement/marring of the head of the cartridge case, cratered primers, flat primers, ripped or ruptured cartridge cases, “popped primers”, and/or any combination of these effects. If any of these “pressure signs”; are apparent, stop firing immediately. If an adjustable gas system is installed, it is advisable to reduce the amount of gas flowing through the system by closing the gas port until the gun operates correctly.
With the installation of an adjustable gas system, gas pressure can be metered to a point that enough gas is applied to open the bolt, but at a slower rate to allow the cartridge case to return to its original diameter prior to the movement of the bolt, and thus allow for proper extraction.
Pressure VS Gas Port Location
Due to the longer duration of peak pressure produced by Superformance™, the post peak/declining pressure at common carbine and mid-length gas port locations is still higher than that produced by standard propellant. However, there is very little difference in port pressure between Superformance™ and standard propellants at the rifle length port location.
Superformance and Suppressors
The use of suppressors on rifles creates yet another dynamic in firearms design that is not commonly understood or communicated. Consider the suppressor on a firearm the same as a muffler on a car. The suppressor works as a filter for the gas (noise) that is escaping the barrel during firing. As a “filter”, it takes longer for the gas to leave the confines of the firearm, and thus, it creates back pressure. This back pressure, ESPECIALLY in a gas operated firearm forces an extensive amount of gas back through the firearm’s operating system that may create too much thrust too early during the firearm’s cycle of operation.
To counteract this back pressure, the use of an adjustable gas system is advised. By metering the gas system to ensure that it will cycle the firearm correctly and not flood the system with gas/pressure, the gun will work properly and will still benefit dramatically from the increased velocity potential of Superformance ammunition.
There were many semi-auto “tactical” rifles on display at MEDIA Day 2013, but one that caught our eye was the new MR762A1 LRP from Heckler & Koch (HK). The HK MR762A1 LRP (“Long Range Package”) looks similar to the H&K G28 rifle, Germany’s new Designated Marksman Rifle. But the G28 has a steel upper receiver, unlike the MR762A1, which evolved from the HK 417.
Bedecked with quad rails up front, this black and tan rifle screams “tactical”, yet it is surprisingly comfortable to shoot. The grip is comfortable in the hand and the thick rubber buttpad on the adjustable buttstock did a good job of mitigating recoil. Jason said the trigger was crisp and the gun was very accurate. With a gas-piston system (rather than direct gas impingement), this rifle runs very clean. The proprietary, polymer HK magazine worked perfectly with zero feeding issues. We liked these better than the metal mags we’ve tried on other makers’ AR10-type systems.
The MR762A1 is a direct descendent of the HK416/417 series, only in a semi-automatic rifle configuration developed for civilian users. The MR762A1 LRP employs the same HK proprietary gas piston operating system found on current HK rifles and carbines, using a “pusher” rod in place of the gas tube in the original M16/AR15/AR10 design. According to HK, the op-rod design “virtually eliminates malfunctions common to direct impingement gas systems since hot carbon fouling and waste gases do not enter the receiver area. The MR762A1 stays cleaner, reducing heat transfer to the bolt and bolt carrier, and drastically reducing wear and tear on other critical components.”
The MR762A1 uses the same 10- and 20-round translucent polymer box magazines made for the HK417; a 5-round magazine is also under development. Additional accessories and add-ons for the LRP variant of the MR762A1 include an ERGO Pistol Grip from Falcon Industries, the same Blue Force Gear sling used on the HK M27 IAR supplied to the USMC, and an OTIS cleaning kit. The rifle package, complete with one 20-rd mag and one 10-rd mag, is shipped ready to use with the scope attached in a 42″-long Model 1720 Pelican case.
A “pimped-out” Turnbull Manufacturing TAR-10 (AR 10-platform) rifle shattered the all-time SHOT Show Auction record with a high bid of $136,024.00. Proceeds from the auction conducted last week will go to support the NSSF’s Hunting Heritage Trust. This unique Turnbull TAR-10, chambered in .308 Winchester, has features rarely seen on an AR-style rifle: color case-hardening, hand engraving, gold inlay, and select walnut “furniture”. The upper and lower are made from 8620 carbon steel that has been color case-hardened with the Turnbull bone charcoal process.
The gun has been elaborately engraved by Adams and Adams, with extensive gold inlay. The butt-stock, fore-end, and pistol grip are select fancy walnut.
“We did our best to make this a very special rifle and we had hopes of beating the all-time record of $83,025.00, but we never imagined the bidding would surpass $100,000 and then soar to more than $136,000.00,” commented Doug Turnbull.
“Our objective in creating the TAR-10 was to show that the AR platform is more than just a military rifle. We wanted to emphasize that these types of rifles can be made to look like any other custom rifle in terms of appeal,” commented Turnbull. The rifle, as sold, was equipped with a Zeiss 1.5-6x42mm Victory HT scope. Regular production Turnbull TAR-10 rifles will be the same as this special SHOT Show rifle minus the elaborate engraving and presentation-grade wood.
Here’s a simple tool that may benefit you AR15 and AR10 shooters out there. The G&G Tools’ Bolt Cleaner and Polisher uses a radiused scraper with a cleaning pad to remove stubborn carbon from the tail of your AR bolts. The G&G Tool is offered in both a .223 version and a .308 version, both priced at $29.99. There is also a more basic (scraper only) unit for $19.99.
There are other ways to remove carbon (soaking in solvent and scraping with a knife), but G&G’s tools make the job quick and easy. Credit The Firearm Blog for finding this device. Watch the video below to see the tool in action.
With a standard AR-15 we’ve never had problems with the standard coil-spring-equipped buffer system (other than the annoying spring noise). But with the AR-15’s big brother, the heavier-recoiling AR-10, an enhanced buffer system is welcome. A upgraded buffer won’t reduce recoil force, but it can soften the perceived recoil pulse, allowing the shooter to get back on target more quickly while reducing shooter fatigue over an extended string of fire.
Buffer Technologies of Jefferson City, MO, has introduced a new hydraulic buffer for AR-10-type rifles. Priced at $99.95, the hydraulic buffer weighs 0.38 pounds, has a 5.8-inch compression length, and fits AR-10s with full-length buttstocks. The buffer, crafted from black-oxided steel and black-anodized aluminum, is optimized for use with the .308 Winchester cartridge.
Buffer Technologies claims that its hydraulic buffer can help prevent failures of internal parts and optics by reducing shock and taming recoil. According to Rob Parham, Buffer Tech’s Military/LEO Sales Director: “Our new buffer makes a great gun even better, while protecting the valuable accessories on the firearm. This product is great in assisting target acquisition and allows for quicker follow-up shots.”
The basic AR15, with upgrades to barrel, trigger, optics and “furniture” has evolved into an extremely effective varminter, chambered in .223 Rem, or a .20-caliber such as the 20 Practical. Hunters have also adapted the AR10 platform, with its ability to fire a .308 Winchester-sized cartridge, for use on deer and Elk. Now ArmaLite has “re-introduced” a handy, compact AR10 carbine that should be ideal for hog hunters.
The folks at ArmaLite received many requests for a lighter, more compact version of the AR10. Armalite responded: “We did a small limited run and we’re pushing its use as a varmint hunter… especially good against wild boars. One of our ArmaLite gunsmiths got the idea from some buddies in Texas who are using their Ts against the wild hogs. This AR-10(T) Carbine combines the light weight and compact size of the carbine with the accuracy of the Target Model.” This AR10(T) carbine features a 16″, 1:11.25″ twist barrel, fitted to a forged, flat-top receiver with built-in Picatinny rail. With a compact 37.5″ length, the gun weighs 8.6 pounds (3.9 kg). Included with the rifle are one 10-round mag, and one 20-round mag. MSRP is $1892.00.
Defying its reputation as a stodgy, conservative organization, the IBS will allow AR-style rifles to compete in their own class at IBS benchrest matches next year. Both AR15-platform and AR10-platform rifles can compete in this new, provisional class.
This will NOT displace any of the current classes (e.g. Sporter, LV, HV, Unlimited), nor change any rules for current classes. The “AR Experiment” will last for one year and then the IBS will determine whether to make the class permanent. IBS President Jeff Stover stressed three points:
1. This is an experiment for a one-year trial.
2. Clubs MAY have an AR class, but they are not required to do so.
3. The IBS Nationals are NOT affected — there will be no ARs at any Nationals
The IBS has distributed proposed draft rules, and the IBS plans to adopt final rules on March 1, 2010. Here are some of the key proposed rules:
Timney Triggers now offers a true drop-in trigger for the AR10 rifle platform, similar to Timney’s successful drop-in trigger for the AR15. The new AR-10 trigger is a self-contained, 100% drop-in unit that can be easily owner-installed (no professional gunsmithing required). The new trigger is a single-stage design with pull weight factory-set at 4 pounds. The trigger module installs using your rifle’s original hammer and trigger cross-pins. The MSRP is $234.95, but we expect the trigger to be available for $210 or so from other vendors.
The new trigger is solidly built and precision-machined. The housing is lightweight, 6061 T6 aluminum alloy, anodized for durability. The hammer is EDM-machined from S7 tool steel for superior hardness and impact resistence, and the hammer is Teflon + Nickel coated to provide greater lubricity and a smooth pull. Other components are EDM-cut from A2 tool steel, then heat treated to Rc 56-60 for longer service life. For more information on Timney Triggers, call (866) 484-6639, or visit TimneyTriggers.com.
Here’s a simple tool that may benefit you AR15 and AR10 shooters out there. The 
Defying its reputation as a stodgy, conservative organization, the IBS will allow AR-style rifles to compete in their own class at IBS benchrest matches next year. Both AR15-platform and AR10-platform rifles can compete in this new, provisional class.
