The best little cartridge you’ve never heard of
By Neil Schultz
For much of my 40-something-year shooting career, I’ve been an advocate of owning rifles chambered in ‘common’ cartridges. Much of my shooting in the late 70s, and through the 80s, was hence undertaken with a .30-06 then a .270, both very commonly used pig, goat, and deer rifles in that epoch. My regular hunting cobbers at the time ran rifles in .243 and a couple also carried the accurate little .222 Rem.
During the past couple of decades, I’ve sent thousands of projectiles away from the barrels of rifles in .308, .243 and .223.
The past few years, however, have seen me stray from my common-cartridge idiom and decide to add a few wildcats to the gun safe. The first was a nifty little .22 K Hornet, which has proven to be the ideal short-range fox cartridge. Other additions to the gun safes at home included a .22-250 Ackley Improved and a .25-06 Ackley Improved, both in long, heavy barrelled rifles. As accurately and effective as both of those rifles are, they are best suited to either shooting from a hide or being transported by a vehicle. Carrying them around the mountains becomes rather uncomfortable in short order.
Hence, I developed the desire for a rifle light enough to carry through the hills, inherently accurate enough for small targets (feral cats) but with enough punch to tip over the odd pig or fallow deer with a reasonably well-placed shot. It took very little to convince myself that a 6mm cartridge based on the .223 bolt face was where I should be looking. Ringing around a few local gunsmiths, I found that a 6mm TCU reamer was available just minutes from home, so that’s what the new project rifle was destined to become.
The TCU series of cartridges were developed by Thompson Centre Arms for shooting handgun silhouette competitions in their Contender pistols. A 7mm variant was first off the production lines in 1980, with the 6mm, then a 6.5mm following a few years later. As one would imagine, being purpose designed for competition these are inherently accurate.
Being an enthusiastic practitioner of buying Australian, I opted to have an old Sportco model 33 re-barrelled. A phone call to the great folk at Swan Firearms had an order placed for one of their superb barrels. I’m unlikely to ever want to shoot heavy projectiles through this rifle so a 1:10 twist 24” barrel was ordered.
The first view of the re-barrelled rifle had me smiling; it looked very sharp. Apart from its neat appearance with the thin 24” barrel, the light weight immediately impressed. Now to get some rounds loaded.
Like all wildcats, cases needed to be made up from other cartridges. The 6mm TCU cases were created by first necking up .223 brass to 6mm without any other changes. These were loaded with 80gr Rexem hollow point projectiles long enough to jam into the rifling to fire form into the finished TCU cases. With 50 of those fire-forming cases loaded, a trip to the local SSAA Ipswich Branch range was undertaken.
Running in the barrel was done as per Swan’s instructions, which took a total of 30 rounds, all sent down range while sighting in the scope, then just shooting groups. Results were pleasing, with all groups sub-MOA even though the barrel was not yet fire lapped. History has shown that (in my rifles) peak accuracy isn’t achieved until a 100 or so rounds have been put through a new barrel.
Now, with fire-formed cases on hand I began the interesting journey to find the load that would give the best possible performance in both knock-down power and accuracy, settling on 27.6gr of ADI 2206H under Rexem 80gr hollow points. These loads went through the chronograph at an average of 2950fps and delivered groups of 3/4” at 100 metres. That is just 200fps and 200ft-lbs less than a .243 running the same projectiles. That was a little surprising, considering the difference in case capacity between the two cartridges. My loads in the .243 are 38.3gr compared to just 27.6 in the TCU running the same powder and projectiles.
For the rig’s first outing, I had mounted a newly acquired Zero-Tech Thrive 4-16 scope via a 3/8 to Picatinny adapter that I had re-engineered at home (read ‘taken to with a hacksaw and file’) to allow easy loading and ejection. This combination of new, free-floating barrel, lightened trigger and rigidly mounted scope proved to be a winner. Groups shot over the bonnet of the ute in very windy conditions ranged from 1” to 0.4”, with a seating depth of 2.34” proving to be most accurate, delivering groups averaging .6 MOA.
I usually use a trip out west to conduct range work on loads or sight in rifles wearing new scopes, etc. This outing was no exception, so once various loads had been shot over the chronograph, naturally a short hunt was in order.
The property on which I was camped has a permanent population of bunnies, a few foxes and very occasionally a feral cat or pig. Oh, it also sees a few fallow deer passing though at times, too. Having a daytime optic perched atop the Sportco dictated an early afternoon start to enable shooting with natural light. Hopes were high for a fox as I commenced wandering around ridges covered with open box forest, button whistle hanging around my neck. I had no interest in any rabbits, which don’t tend to be too numerous in the rocky ridges anyway.
During one of the frequent stops to scan the scrub for a hint of ginger fur, a spot of colour caught my eye. About 250m distant something was moving slowly, almost totally concealed by undergrowth of wattles and hop bush. Cranking the Zero-Tech up to 16X, I braced against a box tree and waited for the wee beastie to show more of itself. The old heart rate increased significantly upon the observed stepping into a gap in the foliage, revealing itself to be a deer. Using tree trunks to block the deer’s view of my movement, a deliberate stalk was undertaken to close the gap. Every tree was used as a rest to steady the scope while I glassed and re-evaluated the distance. Daylight was fading fast, so I wasn’t going to dilly dally. Dropping below the deer’s horizon into a gully, I legged it along to emerge at just 80m or so away; perfect. Crosshairs centred on the deer, it became a waiting game, holding fire until the ideal shot was presented. A meat-saving point of aim saw the projectile hit just in front of the right shoulder, quartering into the vitals and at ‘the report’, he dropped in his tracks.
Due to the absence of an exit wound, I was curious about the performance of the 80gr hollow point sold as a ‘varmint’ projectile. When dressing the young spiker, an ideal meat animal, I found the remains of the projectile, lodged just under the hide of the offside rib cage. That is perfect, with all of the round’s energy dumped within the animal’s vitals. That is ideal for a pill designed for thin-skinned beasties, including cats and foxes along with our smaller game species.
Just a couple of weeks later I was farm-sitting for a friend on a mixed block of grazing and cultivation on the southern Darling Downs. Here was the mission for which the 6mm was destined, with cats, foxes and pigs on the feral hit list. Following the script to perfection, the opportunity to test the 80gr pills on pigs came on the first night. Happily, the little TCU received an A+ report card, with DRT results on pigs up to 60kg. Either shoulder or neck shots were used, depending on the pigs’ size and position, with both proving effective. I wasn’t keen enough to dig out any of the projectiles but penetration through shoulder armour indicated a well-constructed jacket for medium-sized game.
Having now been hunting with the 6mm TCU for a couple of years, it still impresses, punching well above its weight. Accuracy, efficiency and incredible muzzle energy from such a small package – it has it all.
