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.
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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.
What is the difference between this cartridge and the 243 Ackley Improved?
The 243AI has 40 degree shoulder and less neck.
The standard .243 should chamber in the AI for fire forming, the Super LR will not chamber .243 Win, you need to die form those. The AI will be more likely to have greater throat erosion, and as per article less bearing surface.
Ackley did both, the 30 degree and the 40 degree long before Whitley
The 6mm Super could push the 115-grain bullets comfortably at 2950-3050 fps. I would have thought the 6 mm dasher could all but do that?
Just add H1000 and away ya go!
The 6mm Dasher is again short necked. It IMO loses one of the great advantages of the 6BR parent case. The 6MM Super actually adds to the neck in comparison to the .243 Win parent.
I started out with a, take off, Shilen target barrel, chambered in the 6mmRemBR ( Lapua ). I was told that it was a 1 in 14 twist. So when the BR couldn’t be made to cycle through my M-98’s box magazine, I created my own 6mm Wildcat. It’s a 6mm x 300 RCM with extra case taper and a 26 deg. shoulder.
Because of Hornady’s once in three years, production schedules, I have had to make cases out of Nosler 350 Rem. Mag. virgin brass. Finally, some 6.5mm Rem. Mag. virgin brass has shown up. All of these bulge out ahead of their belts and blow out slightly at the shoulders. My case taper has to be ironed into the Rem Brass before firing.
I too, have shorty necks. I should have left Hornady/Ruger’s 30 degree shoulders. They look neat, until I fire form them.
Now the new kids on the block are the newbies 6.5mm PRC, and the 6.5mm GAP 4S. Both of these can be necked down to 6mm, but for what it’s worth, I still like my design, as it cycles through a military Mauser’s magazine. ( Feed rails are slightly ground away to do this ).
I also did a 7mm version and in a 3.3 inch Mauser Mag. I equal the 7mm RSAUM, when that puppy is in a true short action, ( 2.83″ ), when shooting 175 gr. semi spitzers. ( Pull Downs ), so I don’t know exactly which product #.
An ancient Mauser military 7mm barrel was trimmed to 23 inches, and I cut off two tenon threads, to make a crude 2R chamber. But it’s a terror out to our club’s 500 meter gong. But so is the Rem. 7mm RSAUM.
The 6mm Rem. is 57mm, mine is 53.94mm, the 300 RCM is 53mm, the 6.5mm Rem. Mag., and the 6.5mm x 284 Norma are 55mm long.
But consider that these imp. 243’s are all 51mm or less. Shilen said that when their 6mm Rem BR is shot out, the barrel will be toast for some 12 inches. The big bruisers will burn their throats quicker, but you can set them back, re-chamber, and you’re off to the races again, or at least, as ‘lope and yote’ killers.
The real sleeper, IMO, after all of my trials, would be the 55mm long 6mm x 350 Rem. Mag. wildcat. I too would have that reamer ground back to 30 degree shoulders. But in this case, pardon the pun, the belt would still be what head spaces this modified case. So the new 30 deg. shoulders depths, wouldn’t be that critical. My RCM’s .530″ case heads do center these belted jobs, against my Mauser’s claw extractor, but I still have to play with false shoulders in order to safely fire form them.
The 6mm x 350 Rem. Mag. uses a belt, so there’s no sweating, pushing back those shoulders to 30 degrees, and leaving the case a mite short.
Maybe I’m just dense, but these results weren’t that obvious, when I started this project. And neither of the two newbie Hornady 6.5mm’s were around, a few years ago. And both of these 6mm x 6.5mm wildcats/improved barrels can be re-bored and re-rifled, to their parent cases’ factory chambers, down the road.
All of these shorty 243’s will take longer to burn out, but when they do, there’s a 6.5 C.M. in your future, if your magazine cannot handle a 257 A.I.
At least, I can have all of my test beds re-bored and re-rifled out to the 300 RCM, and end up with true 300 Magnum performance, without all of their noise and recoil. My new donor rifle is a Ruger Compact Magnum L.H. which has been a pleasant surprise. It still needs a standard length L.H. action to load three rounds down in the magazine. I figured that in a 6mm, two down are plenty, as it’s no way, any bear gun.
FWIW, with enough meat in the barrel, I can work out to a .430″ wildcat chamber, with just enough shoulder for my PT&G GO Gauge to hang up on. But so will the .416 x 350 Rem. Mag. And these were well known gunstock splitters.
All of Remington’s short belted cases used 25 deg. shoulder angles. And IMHO, this means that the new Hornady 6.5mm PRC, just necked down to 6mm, is poised to rule the varmints’ roost.
To this end, I necked down one each of George’s GAP 6.5mm PRC, and 6.5mm GAP 4S virgin cases, made dummies, and mailed them back to Kansas City, for GAP to peruse. I haven’t heard back to date.
I also have been bugging Ben S. at Hornady’s custom die desk, over a 7mm RCM with a 0.321″ long neck, but they have since gone with their two newbie 6.5’s.
I guess with suburban sprawls, target matches are trumping varmints, and open country Big Game. My 18 inch long barreled Ruger Compact Magnum rifle may be their last real stalking rifle, development. Both my 6mm x 6.5mm PRC, and 6mm x 6.5mm GAP 4S dummies feed O.K. through this CRF Compact Magnum Rifle.
Sadly, it’s only my 300 RCM ammo, and my wildcats, which jam up the feeding, when you put three rounds down into it’s magazine. So now, I hope that I’ve touched all the bases for anyone, here, wanting to make up a CRF rifle in one of these 6mm short mag. hotties, without running into any SAAMI’s Delta problems.
Hornady has been sneakily putting less and less case body tapers into shorter and shorter RCM based cartridges. is this like the 8mm Mauser, and 308 Win. not quite going into the 30-06G’s chamber???
I need to find a good gunsmith to re-chamber my 243 win bolt rifle to the 6mm Super LR. Can someone recommend them to me?
Thanks
Hi.What does LR stand for.
Cheers