Good Evening,
The first phase of testing is complete with regards to using a 6.5 TCU for HP Silhouette. The rifle is deadly accurate and the recoil is, hey what recoil:-) We had our monthly SB/HP Silhouette match in misty Sacramento, CA today. Conditions were muy bueno and a good time was had by all. Cool and misty in the great Terminator State on the Best Coast.
Any way, after years of shooting silhouette starting with Big Bore pistol silhouette back in '79, sure seems to this boy that recoil is the # 1 bane of HP Silhouette. Next in line on the bane scale is wind deflection. What to do, what to do, to drive down both of those scalawags? Well, the manly mantra is "Shoot The BC's." What is meant by that is shoot the highest BC bullet available in your caliber that will stabilize and shoot accurately. Marginally stabilized bullets follow funny paths through their all to short free-flight lives. You don't what to go there, no way Jose!
Now that the above spiel has set the stage, on to for why the 6.5 TCU for HP Silhouette. The abridged version starts with a review of the obvious, that is the most popular caliber for those in the know in silhouette is the 6.5mm. The reason is that caliber, given the readily available bullets in that caliber, offers the best balance of tradeoffs between, ram knockdown performance, wind deflection and recoil. Formally stated the optimum balance of tradeoffs for HP Rifle Silhouette is that load that will deliver 95 to 98 percent ram performance with minimum recoil and wind deflection. The selection of 6.5mm bullets delivers on that optimization goal. There is actually a better caliber, but shooting it requires the design and purchase of costly bullet dies to manufacture a short animal bullet.
If you accept the above paragraph, the next question is which 6.5mm cartridge is optimum. Since we accept that 140-grain VLD's out of 8-twist barrels is the standard, which also qualifies as a readily available optimum solution, the next question is what MV is best for the rams? From much testing and match shooting it seems that between 2,700 and 2,800 fps is about optimum. For the short animals most are shooting 107 Sierras or 108 Lapuas. Those of you that are shooting the 95-grainers are OK as long as there is not much wind, but out here they are not a good choice as wind deflection is enemy # 2 and we are often in mortal combat with enemy # 2.
So, the above begs the question, which cartridge? First the minimum size cartridge that will produce a 2,700 to 2,800 fps MV with a 140-grain VLD is about right. The 6.5 x 08 is over capacity and therefore falls into the overbore category. That means that one will collect more recoil and sustain accelerated barrel throat erosion compared to a smaller capacity cartridge. The 6.5 BR, if throated properly is an excellent choice, the 6.5 TKS is in my NSHO is just about right concerning the optimization process. So, why the 6.5 TCU, which has holds only 29 to 30 grains of N150 if the reamer is designed to shoot the 140 VLD's compared to the 6.5 TKS which can hold 35 grains of N150 and produce 2,775 fps with a 140 VLD. The answer is; there was an old BSA 223 bolt-faced action and a bunch of spare parts to build a rifle with as well as an old JGS 7 TCU reamer that had been collecting 25 years worth of dust. The reamer was reworked by Dave at Pacific Precision. Dave did an excellent job and quick too. AND, most importantly it sounded like fun.
And, fun it is to shoot. One can shoot the rifle with a light, small-bore style grip, as there is so little recoil. The C, P & T load is 26 grains of N140 that launches a 140 AMAX to 2,250 fps. The reason that bullet is shot for the short animals is that the chamber is designed for seating that bullet so the base of the boattail is at the shoulder/neck junction for max case capacity. Also, it should be noted that that round has less recoil and wind deflection that the typical 107 Sierra load launched at 2,700 fps. Why that is so is food for another discussion. The ram load is 29 grains of N150 with the same A-MAX bullet. This load produces a MV of 2,520 fps. That is a marginal MV for rams. If the rams are not bent and set properly and there is no wind holding them up, the rams should just about all go down. The Lapua cases only hold 29 grains of N150, but the Remington cases that still need to be fire-formed should hold 30 grains. This case is so efficient due to its small size compared to the bore that 1 grain of N150 produces an extra 90-fps. So, 30 grains of N150 should produce a MV of just over 2,600-fps with no excess pressure.
This little puppy is a joy to shoot. Several of the guys had a go at giving it a try at the range today. I'm thinking that there will be more of these rifles on the line in the future for those that are more interested in fun than punishment at the ram line. For a youngster or petite woman or any of you old guys that are suffering from shoulder pain from too many years of recoil abuse I'm thinking that the 6.5mm TCU, if throated properly, could be in your collective futures.
All the best,
Dan Theodore
