The 6mm Super LR — .243 Winchester Made Better

In our Forum recently, there was a discussion about “improved” cartridges based on the .243 Winchester parent case. One popular such cartridge is the Super LR, a 30° long-necked wildcat. The 6mm Super LR was developed by Robert Whitley, who wanted something similar to the 6XC, but with “more boiler room” to push the 115-grain bullets comfortably at 2950-3050 fps.

To illustrate the Super LR for interested readers, we dug into our archives and found a report on a 6mm Super LR varmint rifle belonging to Barry O. (aka “TheBlueEyedBear”), a long-time AccurateShooter Forum member. A few years back, Barry put together an impressive 6mm Super LR long-range varminter on a BAT SV action. Barry actually sourced many of the components for this rifle through our AccurateShooter Forum Free Classifieds. CLICK HERE to read all about Barry’s Super LR BAT-Actioned varmint rifle, featured in our popular Gun of the Week Series.

CLICK Photo to Read Full Story

The Richard Franklin walnut LowRider stock (above) for Barry’s rifle came from fellow Forum member “Preacher”, who also did most of the metal work. The gun is chambered as a 6mm Super LR.

6mm Super LR Cartridge Design and Loading Advice
by Robert Whitley, AR-X Enterprises
Conceptually, the 6mm Super LR is like a long-bodied 6XC (case body about .120″ longer). The Super LR has a long neck (.321″ vs. the .263″ long neck of the parent .243 Winchester case). The Super LR also has a 30° shoulder angle vs. the 20° shoulder angle of the .243 Winchester parent case. The Super LR has about 54 grains of H20 capacity, compared to 55 grains for the .243 Win and 49 grains H20 for the 6XC.

The Super LR has sufficient case capacity to shoot the 115gr 6mm bullets in the 2950 – 3000 fps range without being “on the edge” of maximum pressure. If you do not need to run sustained fire in long strings, you can “hot rod” things more. Testing has shown that the Super LR can run the 115s up around 3100 fps without issues. With the 105-108 grain 6mm bullets, the 6mm Super LR can push them up in the 3150-3200 fps range with the right powders. In addition, if you like to shoot the 105-108 grain bullets close to the lands, or engaging the lands, the Super LR cartridge case neck is long enough to give most of them a good bearing surface purchase, even if the chamber is throated for the 115gr bullets. That gives the 6mm Super LR cartridge great versatility.

The 30° shoulder angle of the 6mm Super LR is another good feature of the Super LR. Not only does it help to avoid the throat-torching effect that people associate with the .243 Winchester (because of the .243’s short neck and 20° shoulder angle), but the 30° shoulder angle has also been a hallmark of some very accurate cartridges such as the 6 PPC, 6mm BR, 6XC, and 6.5 x 47, to name a few.

The 6mm Super LR wildcat is easy to make. Robert Whitley figured out how to reform domestic .243 Win brass with one simple pass through a Redding 6mm Super LR full-length sizing die. Robert has commissioned these dies from Redding. Call Robert at (215) 348-8789 to order.Learn more about the 6mm Super LR on Whitley’s www.6mmAR.com website.