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Determining the best chamber for your 6.5mm Creedmoor RPR replacement barrel

Posted by BOLD APP on

LRI's RPR replacement barrels offer the RPR owner the unique opportunity to make an already great rifle to an exceptional one.  With little more than a few basic hand tools, this upgrade elevates the platform to a performance level mirroring custom rifles costing thousands more.

Cartridge choices for the RPR are limited only by two things; bolt face diameter and Cartridge Over All Length (C.O.A.L).  Any short action cartridge with a rim diameter of .472" can be adapted to the RPR with nothing more than a barrel swap.  So long as the cartridge fits in the magazine, your all set.

The 6.5mm Creedmoor is the clear favorite among shooters and for good reason.  Ammunition is relatively easy to source, affordable, and the performance is exceptional.  LRI offers two chamber variations for the RPR in 6.5mm Creedmoor.  Our tooling is optimized for the 140 grain Berger Hybrid and the 140 grain Hornady A-Max and 143 grain Horndady ELD-X.   

Both the Amax and the new ELD-X, are designed to function in the A Max chamber.  This is a good thing as it means existing rifles can transition with predictable results.  The 140 grain Berger Hybrid is also a very popular projectile.  Especially at longer distances.  The ballistic coefficient is quite good which translates into a flatter shooting bullet.

Chambers for these bullets are tailored for maximum performance.  When designing a chamber for a rifle like the RPR, the magazine length becomes the constraint.  If the rifle is to be used as a repeater then the cartridge length cannot exceed what it allows.  

The Meplat (tip), Ogive ("cone"), and boat tail (back end) of a projectile all play critical roles in performance and have a major impact on chamber freebore dimensions.  If we compare the Berger (left) with the Hornady (right) we can easily see the differences in bullet overall shape.  This photo has been edited to exaggerate the transition point between the ogive and bearing surface intersection of the bullet.  This "gauge line" is what determines the freebore length in a chamber because of magazine length constraints.

Freebore is the governing factor.  This is nothing more than a portion of the barrel that is void of any rifling.  It allows for some of the bullet's bearing surface to extend past the neck of the case.  With different bullet designs, freebore can be tailored to deliver the best performance.  This is not to say however that a particular projectile demands its own special reamer.  Bullets, while different, share a lot of common traits that usually only require a couple different options.

In the case of the Amax/Hybrid the freebore is quite a bit different.  The Amax has more bearing surface than the Hybrid.  This means the gauge line is further away from the base of the bullet requiring a longer freebore to optimize the case capacity.  The Hybrid's gauge line extends further back so freebore will be shorter.

The overwhelming question were asked is how does a shooter run both bullets?  

 A Berger will have more "jump" to reach the lands in the Amax chamber.  If we seat the bullet further out to reach them, It can exceed what the magazine allows for a C.O.A.L.  An Amax must be seated further into the case to safely chamber in the Berger setup.  This reduces case capacity and positions the bullet in a location generally understood as less than ideal.  

One possible exception to this scenario is a barrel that has some mileage on it.  If we start with the shorter freebore Berger setup and shoot for awhile it's very typical to see accuracy start to bleed off due to throat erosion. This erosion is the heat/pressure from the powder charge chewing away at the start of the lands inside the barrel.  

It's conceivable that once the Berger no longer reaches the lands, a swap to the A max might bring some accuracy back and extend the usable life of the barrel.  -No promises, but it would be worth the effort before investing in a new barrel.

Hopefully this helps to answer some of the questions surrounding this topic.


Chad D.






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