Why hunters are shifting to smaller cartridges

It wasn’t so long ago that the magnum craze was upon us, with many figuring the extra power and velocity out of a large rifle cartridge was frequently needed. Now, there’s a trend towards smaller, easier to shoot cartridges that allow good shot placement thanks to mild report and recoil. Perhaps improvements in both terminal performance and aerodynamics, as well as new powders allowing smaller cartridges to perform better, have played their part. Many of these diminutive cartridges are being loaded with long, heavy-for calibre, high ballistic co-efficient (BC) bullets which perform well at distances such as 600m, especially on targets. I’m more interested in using extra-short, mild cartridges for hunting up to about 270m, in areas where the terrain and vegetation don’t really necessitate longer shots.

My extra-short action Sako S491 was rebarrelled to 6.8 SPC II in 2007, and since then I have used the rifle as my primary pig gun, but also on goats and smaller varmints as well. The 6.8 SPC II, together with the .308 Win, are my two-favourite hog chamberings. What the extra-short 6.8 SPC II loses in power to the .308, it makes up for in consistently good shot placement. I’ve also been using two rifles in 6mm on smaller deer, varmints, goats and boars. After hearing good reports of extra-short mild cartridges in 6mm, such as the 6 SPC – the less powerful .223 necked up to 6mm, and the newer 6 ARC, I contemplated whether a 6 SPC using medium weight 90gr projectiles might surpass my 6.8 SPC II using 110gr bullets.

So, I decided to build an ultra-light rifle in 6 SPC with a 56cm barrel, the same length as on my Sako 6.8 SPC II and test it with the chronograph, on targets and in the field on game, and compare the two cartridges. The performance of the 6.8 SPC II, which has the same bore size as the .270 Win, on game up to medium size has been superb. Nevertheless, the 90gr 6mm bullets, especially the 90gr Sierra Tipped GameKing with its high BC of .490 and better sectional density, might possibly be even better than the heavier, larger diameter 110s in the 6.8. Especially around the 220-270m mark, which is about as far as I would use either of those cartridges.

Although the 6mm ARC has become a popular factory chambering, I chose the 6 SPC for its flatter trajectory up to 270m with 90gr projectiles for hunting. Also to use a lightweight scope on my rifle to simply point and shoot, without wasting precious time adjusting turrets.

The SPC case has a 23-degree shoulder, feeds better in some rifles and allows five rounds in the magazine, rather than four with the 6mm ARC. Plus, I also have lots of parent 6.8 SPC cases to run through the 6 SPC full-length die to easily form the 6 SPC cases. Usable case capacity when using projectiles up to about 90gr is similar with the 6 ARC and 6 SPC. Longer projectiles start to encroach on powder capacity with the 6 SPC as they can’t be seated out as far due to magazine length restrictions, but I won’t use heavier than 90-95gr.

I had a Total Solutions Engineering 56cm, one in 8″ twist stainless barrel attached to a Howa mini-action and housed in a Pendleton Composite Stock. The flimsy plastic bottom ‘metal’ was replaced with Oregunsmithing aluminium internal magazine and hinged floor-plate bottom metal. Oregunsmithing make a magazine and follower which is specific to the SPC case. The spring on the trigger only allowed a minimum 3¾ pound trigger pull, so I modified the spring to give a 2¼ pound trigger, which is great for a walk around hunting rifle and the same weight as the adjustable trigger on the Sako. I then mounted a Swarovski 3-9 scope in lightweight Talley rings, with the total weight a mere 2.72kg.

My accuracy loads for the 6 SPC, with limited load development because of the shortage of components, are: 28gr AR2208 with Sierra 90gr TGKs at 2810fps and 28.5gr AR 2208 with Speer 90gr Hot-Cors at 2790fps. With this, always remember to start 10 per cent lower in powder charge and gradually work up, checking for pressure signs. Due to the pointy shape of the high BC Sierra TGKs, the reamer was specifically designed with a short throat so that accuracy would not suffer by having the bullets jump a long distance to the rifling. The Sierras are seated at 2.425“.

In comparison, the accuracy loads for my 6.8 SPC II using AR2219 with 110gr projectiles give the following velocities: Nosler AccuBond 2790fps, Barnes TSX 2800fps and Sierra ProHunter 2820fps. Velocity, using temperature stable powders, is therefore similar in both my rifles. Higher speeds (approx. 100fps more) can be achieved in the 6 SPC with double-based powders such as LEVERevolution, but hot Australian summers and availability are deterrents.

In the field, the ultra-light weight of the 6 SPC rifle makes it wonderful to carry, especially up hills and on longer walks. The Sako 6.8 SPC II at 3.43kg with scope is still a good carry weight though, especially after the modifications. And the medium weight Sako is slightly better for consistently getting good shot placement when shooting off-hand or from a poor rest, simply because of the extra weight making it easier to shoot well. The muzzle of my 6 SPC barrel measures .570“ whereas the fluted barrel on the 6.8 SPC II measures .600“. At the bench the 6.8 SPC shoots tight 5-shot groups, whereas the 6 SPC hasn’t shot as well on average with the limited load development and possibly the barrel not fully run-in.

Having five rounds in the magazine with pigs is an advantage both rifles have. The question though, was whether I could tell any difference between the two chamberings at various ranges? I have both rifles sighted-in 57mm high at 90m with the 6.8 wearing a Kahles 2-7 scope as opposed to the 3-9 Swarovski on the 6 SPC.

On a recent hunting trip, four large pigs and a goat were all shot at less than 100m with the 6 SPC. When shot through the shoulder, or through the ribs angling up through the vitals when facing away, the 90gr TGKs performed exceptionally well, killing them on the spot. However, when shot through the ribs into the lungs on broadside shots, the 90gr TGKs, which have a thick jacket, exited through the opposite side ribs with only moderate expansion. This also occurred on a lung shot boar with my .240 PSP launching the 90gr TGK at 3240fps, so the moderate expansion isn’t a result of the 6 SPC’s lower velocity. In this respect, the 6.8 SPC 110gr bullets (ProHunter, TSX and AccuBond) perform better in stopping pigs dead, whether shot through the shoulder or the lungs.

I also have a 6 SPC load for the softer 90gr Speer Hot-Cors which I have used successfully with lung shots. However, I doubt if the Speers will perform as well with shoulder shots through heavy bone as the TGKs do. I prefer the shoulder shot on most game when I can get it, plus the TGKs have a much better BC, so I’ll persist with them until I get the opportunity for longer shots.

At 270m, the 6mm 90gr Sierra TGK with .490 BC at 2810fps muzzle velocity is down 16.5cm, with 19.3cm wind-drift in a 16km/h crosswind. The 110gr 6.8 AccuBond, with a lower BC of .370, is down 18.5cm and wind-drift is 22.9cm. These figures favour the 6mm bullet, but not by a huge amount. The higher BC 6mm bullet also retains more of its velocity, which means it impacts at a greater speed on longer shots.

Reduced loads in 6.8 using AR2206H work well on varmints if you want them for the table, but a windage and elevation change to the scope is required from full-power loads. The 6 SPC is great on varmints such as rabbits and crows due to the reasonably small, slightly expanded bullet hole, but still killing them on the spot with properly placed shots.

A favoured extra-short varmint cartridge is the .222, which launches a 50gr BlitzKing at around 3160fps from its 56cm barrel. The .222 uses fragmenting varmint bullets at higher velocity and is more destructive on small game. However, the stouter 6mm 90gr bullets do not destroy as much meat if you want to eat, say, rabbits, when not headshot. 

My .222 is sighted-in 3.8cm high at 90m as opposed to 5.7cm at 90m for the 6 SPC. Sighting the 6 SPC any lower than 5.7cm at 90m reduces its effectiveness for longer shots on medium game. Less allowance on small varmints for trajectory needs to be made with the .222. Nevertheless, the 6 SPC is fine on varmints, though a bit more expensive to run with the Sierra 90gr Tipped GameKings than the .222 using 50gr Sierra BlitzKings.

Once again, my Sako AI .222 is heavier at 3.51kg with scope than my 6 SPC and the .222 has even less recoil than the 6 SPC cartridge. This makes the .222 better at precision shots at small varmints such as crows when shot off-hand or at medium distances from an imperfect rest.

The 6 SPC, like a 6mm and .257, fulfill the dual-purpose role of a varmint and medium game (up to and including fallow deer) cartridge just about better than anything else. Being such a mild, extra-short cartridge, it can be housed in an ultra-light, relatively short rifle. This has some advantages if you are climbing a lot or walking long distances and carrying your rifle in your hands for a quicker shot.

The larger cartridges certainly do have their place, but for hunting a lot of game, extra- short mild cartridges such as the .17-.222 and .222 for varmints, and 6 SPC and 6.8 SPC are fine for 95 per cent of shots, and in many cases give a greater level of satisfaction.