Over the past 12 years I've been addressing the shortcomings of Larue Rifles by Rebarreling and enhancing them to a level that a 4K+ rifle should perform, mostly out of necessity for myself and other shooter's who want more out of their Precision Gassers and were tired of waiting on the promise of optional Calibers like the 6.5 Creedmoor and 6mm Creedmoor.
In this review I will be discussing the modifications and enhancements I've made to my personal Larue rifles that has truly transformed them to exceptional .3 MOA rifles with 100% reliability.
As many of us know Larue Large Frame Gassers have always been in a category considered as heavily proprietary, and seem to perform best when using Larue and Larue only part's.
Due to the nature of LaRue LF rifles being designed specifically to work best with LaRue products sometimes it can be extremely frustrating for Shooters who have already spent thousands of dollars acquiring non LT suppressors that don't seem to play well (depending on Flow design) with thier current rifles and in some cases require troubleshooting and tuning of the Buffering Mass and Spring Rates and even then it can still be finicky, especially when running multiple hand loads that may be at a lower pressure compared to factory ammo ultimately causing a variety of malfunctions.
The majority of malfunctions can be contributed to LaRue's Port Select Gas system. The (PST) can be extremely effective but offers a very narrow window of operation that can negatively affect reliability when introducing any changes that may push it out of its designed operational tolerances, it's just not a one size fit all design.
Unfortunately not many people understand how the (PST) Gas Block works. Removing the Larue PST AGB isn't difficult if you know what you're doing, there's tons of incorrect information that the ignorant regurgitate and pass on especially with the ARF.COM know- it -all's.
Most think the Larue PST AGB turns off/switches between two different sized gas ports, the smaller most forward Gas Port for Surpressed and the rear largest Port for unsuppressed. While that theory would make sense that's not how it works.
As mentioned above the Larue (PST) AGB and Barrels utilize two different sized ports that control the flow of gas. Keep in mind the actual Gas Block portion itself is only about 1" and the remaining is to house the parts for the port selector.
As shown below the Port Select lever actually only controls the smaller port, it doesn't even come close to the Larger port that ALWAYS remains open.
The Large port actually does double duty, when the (PST) is set in the Surpressed mode the single small port in the switch shown above in the Surpressed setting is rotated blocking off gas to the smallest gas port.
Once you throw the gas selector switch over to Unsurpassed the selector with the small port rotates over and aligns with the small Gas Block port allowing that extra gas needed to come up and to be fed/transferred back to the larger rear port feeding all the gas into one port and increasing the gas flow.
As you can see from the picture above when you shine a light in the port selector bore that runs directly underneath the gas tube and it runs the entire length of both ports.
Hopefully this clears up some of the details of the (PST) and its limitations.
The OBR
There's no denying when Mark LaRue came up with the design of the OBR he truly invented something quite special, with its 100% True Free Floating barrel design and 20 MOA monolithic one peice top rail, all incorporated into probably what is the most robust heavy duty receiver and handguard design that is damn near indestructible.
Over the years I've Rebarreled more Large and Small Frame OBR's than I can count. There are some slight differences between the two, they both directly attach the handguard to the uppper by four Torx screws but the Large frame uses a direct attachment to the handguard / Mono 20 MOA top rail and the small frame utilizes a type of tongue and groove design that secures the handguard by pinching the 10 MOA monorail in place.
Throughout all the Larue's I've worked on I've come across a few that where in fact not free floating due to the barrel nut making contact inside the handguard, mostly OBR's. It pays to remove your handguard and look for obvious signs of the barrel nut making contact. To alleviate this issue I just removed material from inside the handguard around where the barrel nut sits.
With the OBR having a shorter Handguard I decided to have Paul Ross turn me a Custom 18" 6.5CM Bartlein.
Starting from the Muzzle Brake to the Stock here is the build list breakdown as it currently sits.
Area 419 Hellfire Match 6.5 Muzzle Brake.
Custom 18" 6.5CM / 4 Groove Bartlein/ M110 Contour / Oversized Barrel extension for mandatory thermofit / 1-8 Twist / .875 Gas Block Journal/ 5/8x24 Threads and Rifle Length Gas System headspaced to the Updated Larue HP Small Firing Pin bolt, and have since upgraded to all Larue HP bolts.
Seekins Precision switch lever .875 Adjustable Gas Block. (Will be replacing with a Rifle Speed AGB). Again having the capability to fine tune the gas system over the Larue PST has been a fantastic upgrade that has solved any and all functioning issues no matter what ammo or suppressors are used on the rifle.
Battle Arms Development 60/90 Ambi Safety.
Ergo Grip
Raidian Raptor Ambi Charging Handle.
Due to the Short 18" 6.5CM with RLG I'm running a H3 JP SCS with the stiffest Red/Yellow Spring inside a Dark Hour 11 position Carbine Buffer tube that allows for ultra fine Length of Pull Adjustments when running a stock like the B5 Precision, I have since moved back to the Magpul PRS Lite Adjustable Stock.
JP Ambi Magazine Releases.
Triggertech AR10 Two Stage Diamond with Pro Curved Trigger Shoe.
The original barrel was a LW-50 Pre XTRAXN and shot decent with a
consistent .75 MOA average. As I'm sure everyone here has heard tales from LaRue Fanboys how thier OBR is a Sub Half MOA all day gun, but in reality the people who boast about their accuracy try to substantiate these claims by posting a few cherry picked groups. I don't think I've ever seen anyone shoot a 6x5 to show thier true MOA average.
The Upgrades on this have truly transformed the rifle in to what a 4K + Gasser should be with a honest Sub Half MOA average.
While performing load development the OBR still averaged Sub 1/2" MOA.
I ended up selecting 140 ELD /40.4gr H4350 / Lapua SRP Brass / CCI BR4 Primers. Most of my 6.5CM Bartlein Barrels that Paul Ross turned all shoot this load very well.
Part (2) .308 FDE PredatAR Coming tomorrow. 28MAR24
Part (3) PredatOBR .308/6.5CM Coming 29MAR24
