The Bear’s 6mm Super LR Varminter
Here’s a high-performance varminter built up by our friend Barry 0. (aka TheBlueEyedBear) with metal work by fellow AccurateShooter Forum Member ‘Preacher’. This handsome rifle features a BAT SV action in a laminated walnut LowRider stock from Richard Franklin. The 30″ Krieger barrel was chambered for the 6mm Super LR, a .243 Win-based wildcat developed by Robert Whitley. Whitley figured out a simple way to give the venerable .243 Win a longer neck and a 30° shoulder angle. The longer neck lets you run both long and short bullets at optimal seating depths. You can throat a 6mm Super LR to position long-shank 115gr DTACS above the neck-shoulder junction, and you still have enough neck to seat 90gr to 108gr bullets into the lands. Barry’s 6mm Super LR can launch heavy 6mm bullets at 2950-3050 fps, with no pressure issues. That makes the 6mm Super LR an appealing choice for match shooters and tactical competitors as well as varminters.
6mm SUPER LR (2010 project)
by Barry O. (aka “TheBlueEyedBear”)
Late in 2009 I decided I wanted to build a new long range varmint rifle for the 2010 season. My first knee-jerk reaction was to go with the perennial choices of the 6mm Remington Ackley Improved (6mm Rem AI) or the .243 Winchester Ackley Improved (.243 AI). I started my investigation on these two cartridges and found an AccurateShooter.com article written by Richard Franklin that outlined the advantages of the 6mmRem AI over the .243 AI. After that read, it looked like the 6mm REM AI was the way that I would go. I really liked the idea of having the additional case neck length that was provided by the 6mm Rem AI that would help in providing a greater selection in bullets.
I immediately started to shop the AccurateShooter Forum classifieds for components for this build. As I usually do, I looked for the best components that I thought would make this a real shooter. And I adhered to that old saying, “buy the best and cry once”. Shortly thereafter I found a Richard Franklin LowRider stock that “Preacher” had for sale. After some real serious bargaining (think I knocked $.05 off the asking price) J I made the purchase from Bruce. I then found a BAT SV action, RB/LP/RE at Bruno Shooter’s Supply and purchased that. The remaining items followed shortly thereafter including a Nightforce NSX 12-42x56mm scope that I got at a great price. I think the reason for the good buy was the NP-1 reticle. That was quickly changed to NP-2DD to match my other four scopes in my collection. There was still one problem with the scope: it had over 40X max power. IMHO, I believe that scopes with that much magnification are better suited for Benchrest matches.
Choosing Final Components — And a Smith
I also purchased a Jewell trigger, BAT trigger guard, BAT rings and base, and a Graco recoil reducer (I hate recoil). Oh, and I ordered up a 30″ Bartlein 5R, .237 bore, 5R barrel. There are many good barrel-makers, but it is hard to go wrong with a Bartlein cut-rifled barrel.
Then came the chore of finding a gunsmith that could do the work in a reasonable time frame. Of course that would mean a completion date of yesterday. Like everybody else, I am always in a hurry for my new gun. Anyway, I had no luck finding a “quick-fix” gunsmith. I was chatting back and forth with ‘Preacher’ when he mentioned that he was thinking about building a new varmint rifle. Before you know it we agreed that Bruce would do my metal work in return for the reamer and a few pictures of dead presidents. This was working out well since Bruce did the bedding for the SV action in the stock I bought from him.
Research Points to New 30° Long-Neck Variant of .243 Win
While all this searching was going on I came across an article on AccurateShooter.com about .243-based Wildcats and Robert Whitley’s SUPER LR (originally called the ‘Super X’). I read this article and was instantly hooked. [Editor’s NOTE: Whitley’s goal in creating the 6mm Super LR was to create a simple-to-make wildcat that could drive the 115s to 2950-3000 fps comfortably, but that would be less of a barrel-burner than the .243 Win or .243 AI. The long neck would also allow a throating to suit a wide range of bullets.] I went to Robert Whitley’s website and continued reading about the 6mm Super LR cartridge. This read revealed some very interesting data for a .243 cartridge, along with some very impressive numbers! The Super LR has a 30° shoulder angle vs. the 20° shoulder angle of the .243 Winchester parent case. And, the Super LR has a case capacity of approximately 53-54 grains of water weight versus 55 grains H20 for the .243 Winchester and 49 grains H20 for the 6XC. Whitley had found that his 6XC could not reach the optimal 2950-3000 fps velocity range for the 115gr DTACs. He felt he need a cartridge with more “boiler room”. As Robert says: “The 6mm Super LR has the case capacity of a .243 Win but the long neck and 30° shoulder angle of a 6XC — it’s the best of both worlds.”
QuickLoad Projects Good Velocity with Moderate Pressure (54525 psi)
Here is my QuickLoad output for 43.59 grains of Hodgdon H4831sc with Berger 108gr Match bullets, seated OFF the lands, at a 2.800″ cartridge overall length (COAL). Note that I am using a 53.0 grain case capacity with is slightly different than the 54.0 grains Robert Whitley lists. You should measure the H20 capacity of your own cases after forming and full-length sizing. Note: The pressure and velocity numbers are only a software projection, and this chart does not guarantee that a similar load is appropriate in your gun. Many variables can affect pressure. For example, my barrel has an 0.237 land diameter. A barrel with an 0.236 land spec could show more pressure with this load. Additionally, pressure levels can change with different powder lots, different primers, and different COAL.
Brass Forming is Easier with Domestic Brass
The 6mm Super LR was the cartridge I was looking for — something with the capacity of a .243 but with a more efficient, modern shape. I immediately called JGS and ordered my reamer for the SLR. When the reamer came I sent all the components to Bruce and in no time it seemed like he had the build complete. I had sent him some rounds for test firing that had been formed and loaded based on Whitley’s writeup except for the fact that I used LAPUA brass. DON’T do that!! I took so much time forming the brass, turning the necks, and still they turned out NOT to be the right match for this cartridge. Pay attention to what Robert says about the Lapua brass. Domestic (US-made) brass forms more easily. Lapua brass is thicker in the shoulder than domestic brass, so, when you form the longer neck from the shoulder material, it takes more effort AND you get a ridge or donut. Whether because of this, or something else, the rounds that I formed with Lapua brass just would NOT perform as well as the rounds I later made with domestic brass.
Bruce had some Winchester-brand brass available and he loaded some rounds that worked well for his test firing. When I received the rifle from Bruce I prepped some Remington brass I had purchased then weight-sorted them. With the thinner shoulder-walls in the Remington brass, it is much easier to create the longer neck and 30° shoulder. This was my first experience using something other than Lapua or Norma brass in a long, long time. After the sorting process, I was pleasantly surprised with the Remington performance (for the first go-around of shooting). We’ll see how they hold up.
Hodgdon 4831sc with Berger 108s Works the Best
Another thing I soon learned, Robert was quite accurate in his choice of powder; Hodgdon 4831sc. When I was first trying the 87gr V-Max I thought maybe the IMR 4831 would deliver a little more ‘poop’ to the load. This was evident in my target: it looked like ‘poop’. Bullet holes were inconsistently and randomly scattered all over the place. I switched back to H4831sc and you guessed it — the groups really shrank up. I then moved up in weight to the Lapua 105gr, the BIB 108gr BT, and the Berger 108gr BT.
I got really good results from all except the BIB 108s. I just could not pin them down. Perhaps they require a slightly different twist barrel. The tangent-ogive Berger 108gr BT turned out to be the magic ‘pill’ for this build. This load of H4831sc with Berger 108gr BT (non-VLD) bullets really shoots. My next experiment will be with the new 100gr bullets from Cutting Edge. They are shorter than the previous 100-grainers and should work well with my .120 free-bore. I am really excited to try the new Cutting Edge bullets with their (advertised) high BC of 0.560. Cutting Edge claims this G1 BC has been verified by 1000-yard chronograph testing.
Conclusion — I Love this Rifle (and I Hate Recoil)
Once I switched to domestic brass, and focused on the Berger 108s pushed by H4831sc, the gun demonstrated excellent accuracy. And the 6mm Super LR can drive big 6mm bullets to serious velocities. But this gun doesn’t beat you up. As I mentioned earlier I HATE RECOIL! So, this gun was built with a Harrell’s Muzzle Brake, Graco internal Recoil Reducer, AND a Limbsaver recoil pad. In combination, those three components dramatically reduce recoil. With my new 6mm Super LR, I can see bullet impact — something important when varminting at long range. That’s a pretty nice accomplishment when shooting an 108gr bullet at over 3000 fps.
I would like to give a special thanks to Bruce Griehm (aka ‘Preacher’) for all the work he did putting this rifle together for me. It was kind of ironic that I purchased the stock from him initially then ended up sending it back to him for the build. Also thanks to Robert Whitley for all the work he put in to developing this cartridge and especially the many hours Robert devoted to load development. I am NOT one of the ‘gifted’ shooters who appear so often on this site, so the hard work from these guys is deeply appreciated.
Specifications for this 6mm SUPER LR build:
BAT Machines SV Action — Right Bolt, Left Port, Right Eject
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.
6mm Super LR Dies are Available from AR-X Enterprises
If you already have a 6XC Redding Comp Seater for the 6XC, you can use that for bullet seating, but you may have to re-adjust the die position due to differences in neck length and throat position. In addition, if you already have a 6XC die set, you can run properly-lubed .243 Win cases in and out of a 6XC sizing die with the die approximately .120″ up from the position it would normally be used. Using a 6XC die set for the 6mm Super LR is a little bit tricky, but it can be used, although the sizing die does not hit the bottom .120″ of the brass on re-sizing. Since factory 6mm Super LR sizing dies are available, the best option is to purchase and use them.
Forming 6mm Super LR Cases
For an easy “no neck-turn” brass option with no initial trimming either, use a chamber reamer like one of those shown on this page with either Winchester-brand .243 Win. brass (my favorite) or Remington-brand .243 Win. brass. Both of these have shoulder metal that is right around the same thickness as the neck metal of the brass, so that when you re-form the shoulder of the case there are no “donut” issues. Imported .243 Win. brass (Lapua and Norma) and Nosler Custom .243 Win. brass all have shoulder metal that is considerably thicker than the neck metal, and reforming these to the 6mm Super LR makes a “donut” at the base of the neck that requires the cases to be neck-turned after forming.
I have experimented with all types of .243 brass with the 6mm Super LR, and honestly, the Winchester or Remington brands of .243 Win brass perform very well. First off, it’s easy to reform these brands to the 6mm Super LR case (just run the cases through the full length sizing die, and that’s it, no neck turning or initial trimming necessary). Secondly, these brands of brass are very reasonably priced and readily available. Finally, with some basic weight-sorting of the brass, and the culling out of an oddball case here and there, it’s easy to wind up with batches of brass that exhibit very high quality and consistency.
Loading for the 6mm Super LR — .243 Win Data Works
The first testing done with the rifle was with H4831SC powder, and a load of 43.5 grains seemed very accurate at 100 yards with the DTAC 115s. When this load was chronographed, the muzzle velocity of the 115 DTACs was right around 3000 fps (right in the target velocity range). The load seemed to be “good to go”. I note that Barry O. has also had excellent luck with H4831sc using the Berger 108s.
For more information on the 6mm Super LR, visit Robert Whitley’s website, 6mmAR.com and navigate to the Super LR page. There you’ll find more load tuning info, multiple reamer prints, and tips for bullet seating with various freebore lengths.