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Back to the Future: The 308 MCH
This 1988 wildcat compares favorably with modern short fat cartridge performance.
By Michael C Henniger
The 308 MCH wildcat design is eighteen years old. It was copyrighted in February 1988. A short fat 30 caliber cartridge based on a 404 Jeffrey parent case, it was intended to duplicate the highly accurate PPC cartridges but scaled up to 30 caliber in order to fit in short actions for a lighter, quicker handling and very accurate rifle.
Back in 1987, a friend of mine, Phil Fischer of Portland, Oregon was producing custom magnum actions from surplus large ring Mauser military actions. As a by-product of his process, the parts necessary to make short Mauser actions were also produced. But Phil never made a short Mauser action. Existing cartridges to fit a short action lacked the power to justify a large ring Mauser action. Phil’s regular clientele wanted the big boomers! I thought a custom made short action Mauser would be really sweet. If a better cartridge was needed to justify such a project, why not invent one?
The 6mm PPC, developed by Louis Palmisano and Ferris Pindell in 1975, is arguably the most accurate cartridge ever invented. In 1987 it dominated bench rest shooting as it has ever since. Originally formed from 220 Russian brass, the 6mm PPC is short, fat, and has a small rifle primer and small flash hole unlike the large rifle primers found on many American cartridges. These design elements seemed to contribute to efficient and consistent combustion, which in turn gave superior accuracy. The 6mm PPC's case capacity, case size to bore size ratio, and its internal ballistic properties were in an ideal relationship. So the 6mm PPC design seemed to be a good place to start in seeking a more powerful short 30 cal cartridge.
I chose a bullet diameter of .308 due to the excellent 168gr Match King. The percent diameter increase from 6mm to .308 inch is 127 percent. I began searching for a rimless “parent case†that was 127 percent larger than the 6mm PPC base, which would also fit a rifle with a conventionally sized bolt face. There was only one practical candidate, the 404 Jeffrey; a rimless British cartridge designed for dangerous game in bolt action rifles.
The final 308 MCH design is very close to an oversized 6mm PPC. I was particularly pleased with the proportional relationship between the small rifle primers in the 6mm PPC compared to the large rifle primers used in the 404 Jeffrey. Duplicating the uniform ignition of the powder column in the 6mm PPC was an import criterion for the new cartridge. The final design with the Sierra 168 gr Match King had an over all length,COL) of 2.8 inches. Case gross water capacity is approximately 60 grains, neatly between the capacities of the 308 Winchester and the 30-06 Springfield. The final case dimensions and the name “308 MCH†were copyrighted in February of 1988.
To chamber a rifle and make ammunition for a new cartridge you need reamers of the proper dimensions and headspace gages. A blueprint was sent to reamer maker Hugh Henriksen of Talent, Oregon.
Hugh is a highly regarded reamer maker in bench rest competition circles who was known for the tight accurate chambers his reamers produced. Being in demand, he was not known for fast turnaround times. Six months after I ordered the reamers and gages, I moved. Although I filed a forwarding address with the post office, which is kept for six months, I did not remember to tell Hugh. When my turn for a reamer finally came, his correspondence to me was returned by the Post Office. This story almost ended right there, eighteen years ago.
After Winchester introduced the 300 Winchester Short Magnum, the designer of similar cartridges who held several patents filed a patent infringement lawsuit. Attorneys for Winchester searched for similar cartridge designs among all the known wildcat designs in an effort to show these patents should not have been granted. The attorneys found my design through contact with Hugh Hendrickson. My design was included in Winchester’s defense materials because it preceded the 2004 patent dates by 16 years.
Winchester’s attorneys had Hugh make the reamers, had RCBS make dies to form cartridges and to reload 308 MCH ammunition. They had Ward Dobler of Dakota Arms build a rifle. The 308 MCH cartridge was then tested by a ballistic laboratory to determine pressure and velocity performance.
In the end, the parties settled their lawsuit without a trial. As a result of their settlement, I received the form dies, a two die set for reloading the 308 MCH, 85 formed cases, and a Ruger M77 Mark II short rifle action which had been re-barreled with a Lothar-Walther stainless steel barrel in #3 taper with a 1 – 10 inch twist. Also included were the lab tested velocity and pressure results for the 308 MCH using the 168gr Sierra MK, Federal primers with Hodgdon’s Varget and Vihta Vuori N-150 powders.
The results of these tests are summarized in Table 1.,Cases formed from different head stamps will have slightly different results due to case volume variations.) This testing did not attempt to determine accuracy.
Bullet Primer Powder/ Charge Low Pressure High Pressure Aver. Pressure Low Vel. High Vel. Aver. Vel.
Sierra 168gr M. K. Fed. 210 N-150 / 47gr 51,600 53,600 52,440 2699 2750 2719
" " N-150 / 49gr 56,800 58,500 57,260 2811 2828 2818
" " N-150 / 51gr 60,300 62,700 61,100 2893 2918 2904
Sierra 168gr M. K. Fed. 210 Varget / 48gr 55,400 57,100 56,280 2773 2800 2787
" " Varget / 50gr 59,900 62,000 61,160 2885 2909 2901
" " Varget / 52gr 64,500 66,600 65,380 2982 3007 2995
With any rifle, some component combinations are better than others. Working up loads for accuracy, velocity and pressure is the only way to prove the value of the 308 MCH. Due to variances in case weight in the four head stamped sample, I purchased 50 new Norma 404 Jeffrey cases to form into the 308 MCH. These would be used for the load testing.
Forming the 308 MCH takes thirteen steps: form in dies #1, 2, 3, 4, 5, trim, ream the neck to 308, outside neck turn, anneal the neck & shoulder, fire-form, re-trim to length, outside neck trim, full length resize. The form dies push the shoulder back and reduce the neck diameter to its final size. Like all bottleneck cases, the 308 MCH headspaces on the case shoulder. It is therefore critical that the 404 Jeffrey cases be fully bottomed out in the form dies to ensure the shoulder is pushed back to the proper position. Form die #5 is also the trim die. The wall of 404 Jeffrey brass is much thicker at the new location of the shoulder and neck of the 308 MCH, so the neck wall thickness of the 308 MCH must be reduced. An inside neck-reaming die accomplishes this task. ,The photo shows the results of the case forming steps with a 300 WSM shown on the far right for comparison.) Outside neck turning uniforms the neck wall thickness.
Annealing,softening) the case neck and shoulder will make the final full length sizing job easier. Brass strain hardens due to cold working and a lot of brass was being pushed around during the initial forming operations. As a result, the necks and shoulders of each case will be work hardened making full length resizing difficult. To make the brass soft again, it must be heated to about 750-800 degrees then quenched in cold water to stop the process from overheating the cartridge base.
The process of annealing the brass is both time and temperature sensitive. At 600 degrees the case is softened in 40 minutes or so. At 800 degrees it takes only seconds. Over 900 degrees and the zinc will start to flow out of the brass alloy ruining the case. The bottom of the case must not get too hot or the case will be ruined.
After annealing the cases, the cases are fire formed by using 15 gr. of a fast pistol powder and a filler such as Cream of Wheat. The case shoulder thickness is 18 to 20 thousandths and has only been roughly formed by the dies. Fire forming cleans up the shoulder, which will slightly change case dimensions. In some cases, a portion of the shoulder will form a slight “dough-nut†at the neck shoulder intersection. Therefore, inside reaming may be needed for some cases. Final trimming to length and neck turning is followed by a full length re-size and the cases are now ready to load.
Before actually shooting the rifle, installing a scope was necessary. An early 6X Redfield Bear Cub was available. I liked the look of the old Redfield Bear Cub. The scope was sighted in using the 48gr Varget load listed above. The accuracy at 100 yards was encouraging, but flyers revealed a need for further accurizing the rifle.
Keith Christiansen of Yacolt, Washington did the accuracy work. By free floating the barrel and pillar bedding the action, the negative effects of barrel heating and recoil are reduced. Keith also replaced the stock trigger with a Dayton trigger adjusted to three pounds with no discernable creep. Also at Keith’s suggestion, the 6X Redfield was replaced by a 25X Lyman LWBR target scope. The new scope was bore sighted, and then it was back to the 100 yd range.
Since the 308 MCH design is an extension of the 6mm PPC, its accuracy potential was expected to be high. Determining the real truth meant shooting with a variety of powders, bullets and primers. There is no “published†loading data for the 308 MCH so my only guide was the limited testing shown in the table above. I picked Benchmark, H4895, Varget, Reloader 15 and H4350 as the powders for my initial tests. For bullets, I used Sierra’s 155, 168, and 175 grain Match Kings. I used cases formed from Norma 404 Jeffrey brass, culled by weight to between 237 – 238 grains, and Federal 210 primers. I did outside neck turn the cases as the rifle’s chamber has a tight neck. After testing fifty powder and bullet combinations, the best loads for 100 yd. accuracy were:
Bullet Primer Powder/ Charge Low Vel High Vel Aver. Vel Ext Sprd Std Dev 5 Shot Group
Sierra 155gr M. K. Palma Fed. 210 H4895 / 49.0gr 3,008 3,038 3,020 30.00 20.00 0.625
Sierra 168gr M. K. " RL-15 / 49.5gr 2,950 3,000 2,975 28.11 28.28 0.950
This is all very preliminary. There are other good powders and bullets to try. The weather here in the Pacific Northwest has turned making shooting at the range spotty. But all in all, this is a fun project with potential for both hunters and target shooters.
More to follow in the spring.
Mike Henniger
