260 Terminator: Initial Review

The second cartridge from Defensive Edge with the Terminator designation, the 260 Terminator is based on the 260 Remington case and is designed to fire a 140 grain 6.5 mm bullet at 3000 fps while feeding through a standard-length detachable box magazine.

When Defensive Edge’s owner, Shawn Carlock, told me of his intent behind the 260 Terminator, I listened closely while the wheels started spinning in the back of my mind. A cartridge that can be fired from the same platform as its 260 Remington parent case while providing the downrange performance of the much larger 6.5×284 should pique anyone’s interest.

With my favorite 260 Remington beginning to show its round count and a scheduled PRS match coming up, I asked Shawn if he would be willing to chamber a barrel I had in 260 Terminator for some serious testing. He agreed, and a few weeks later we had an after-hours machining session. Three days later I was shooting tiny groups on paper with it and collecting data.

This article will cover the concept, design, and introduction of the 260 Terminator, as well as the initial performance testing I’ve done with it. Be sure to subscribe to the website for follow-up info throughout the year.

Shawn Carlock and Bob Carlock with a Defensive Edge LRKM

Defensive Edge specializes in designing, testing, and building long range precision rifles.

Located in Rathdrum, Idaho, Defensive Edge is probably best known for the popular long range hunting cartridge that bears its name, the 338 Edge. Defensive Edge (DE) builds a full spectrum of rifle packages suitable for any type of precision rifle shooting, but specializes in long range hunting platforms such as the Canyon Rifle and LRKM. Shawn’s dad, Bob Carlock, handles the rifle building. He is a master machinist and a true craftsman. In recent years, Defensive Edge’s compact chassis rifle, the LRKM, has been keeping him busy. A popular chambering when ordering the LRKM is the original Terminator cartridge, the 338 Terminator. Firing a 300 grain Berger OTM bullet up to 3200 fps, it’s potent long range medicine and is the basis for its 6.5 mm little brother.

Lapua 260 Remington case with a rough-formed 260 Terminator case

At first glance, the 260 Terminator looks like a 260 Ackley Improved (AI) with a different name, but the key difference lies in the +P throat design.

Patented by Shawn Carlock, the +P throat uses stepped rifling at the throat to change where peak pressure occurs while maintaining precision. Think of it as a running start for the bullet. As the bullet leaves the case it’s supported by a shallow section of rifling. This shallow section allows the bullet to be partially engraved and supported before reaching peak chamber pressure and slamming into the full-profile rifling. By experimenting with the depth and length of this step, an ideal balance of velocity potential and accuracy can be reached. I won’t profess to know everything about the concept, but I can tell you that it works very well. A side benefit seems to be less sensitivity to bullet seating depth and concentricity while handloading. The two previous +P throated rifles I’ve worked with were very easy to load for. This one is, too.

While the +P throat design allows all of this cool stuff to happen, the standard 260 Remington case needed some help to optimize those gains. Much like an Ackley Improved case, the 260 Terminator’s shoulder is blown forward, flattened out, and the body taper is decreased. Instead of 40 degrees, it uses a 35 degree shoulder. A quick test shows a fully-formed 260 Terminator case adds three grains of H20 weight over a standard 260 Remington.

The 260 Terminator and gear for the match.

The 260 Terminator chamber was cut in a Krieger Remington Varmint/Sendero contour barrel, finished at 26”.

This is my first Krieger barrel. For that matter, it’s also my first cut-rifled barrel. So far, it’s been quite impressive. Ordered from their Krieger Direct in-stock barrel inventory, it has a standard four-groove rifling profile and no fluting. It’s cut with a twist rate of 1-8”, which works very well for .264” projectiles in the 130-140 grain weight class. Finished at 26”, the blank is listed as weighing 4 ½ pounds. All machine work was performed by Shawn Carlock, including the installation of DE’s three-port muzzle brake. The importance of being able to stay on target during recoil mandates the use of an efficient brake, and DE makes a good one.

Defensive Edge 3-port muzzle brake.

The action used is a Remington 700 that started its career as a 260 Remington. Built for me by Defensive Edge several years ago, the original Hart barrel logged over 3,000 rounds before its accuracy degraded to > .5 MOA. It wears a McMillan A-3 marble-finished stock with equal parts olive, black, and tan. For a consistent cheek-weld DE installed one of their Kydex adjustable cheek pieces. A Jewel HVR trigger set at two pounds and Surgeon bottom metal round out the package.

On top, a Nightforce ATACR 5-25×56 F1 rides in Nightforce medium-height Ultralight rings. Mounted on a Nightforce 40 MOA steel rail, that combination provides 87 MOA of turret travel up from a 100 yard zero. To keep the reticle plumb, a Defensive Edge ring cap scope level is mounted to the rear ring and an Accuracy 1^st ACD rides forward of the turret housing.

Initial load testing for the 260 Terminator showed excellent accuracy potential and a muzzle velocity range of 2950 to 3030 with 140 grain Berger bullets.

With the Rock Lake PRS match coming up in three weeks, I decided to focus on bullets I had on hand, in quantities large enough to develop a load and shoot the match with. Shawn also gave me access to the files of data he had produced during the initial development of the cartridge. He’d been working on the 260 Terminator since late 2014, so I had a good road map of data to follow. Before I could begin though, I needed some 260 Terminator brass.

The jig built by Bob Carlock to form 260 Terminator cases.

Starting with 230 pieces of new Lapua 260 Remington cases, I went through the process of forming them into 260 Terminator.

The first step was to fill the case with a mixture of WSF powder and corn starch. Then the neck is sealed with a wad of paper towel. Rather than directly fire-forming them in the rifle, I used Defensive Edge’s forming jig.  It consists of a bench-mounted barreled action chambered in 260 Terminator, complete with an air nozzle to clear the residual corn starch left after firing. The whole process is simple and efficient, doesn’t waste expensive bullets or barrel life, and because the jig’s chamber was cut with a 260 Terminator sizing die reamer, the cases were ready to be loaded after sizing the neck.

Shawn provided me with a set of dies in a 260 Terminator-labeled Redding die box. The sizing die reminded me of a Redding FL bushing die. Using a Newlon Precision die blank, Shawn chambered it with a 260 Terminator sizing reamer. The top of the die has a cavity for a standard Redding neck bushing. With Lapua brass, I used a .293” bushing for a projected .001” neck tension. The seating die is a Redding Competition Seating die with the support sleeve modified for the Terminator’s body taper.

I asked Shawn if there was any complicated voodoo crap involved with reloading for the 260 Terminator. I suspected not, because we think alike when it comes to the subject of reloading for our long range precision rifles—we would rather spend more time shooting and less time loading. We have little patience for any part of the process that doesn’t produce measurable results. He assured me it would be simple, and he was right. I was shooting the rifle that afternoon.

Lapua brass was used for the 260 Terminator testing.

Shawn’s initial testing used Remington brass. Because I was using Lapua brass, I knew I wouldn’t have the same capacity.

Previous experience told me I would have to reduce my loads by two grains to offset the reduced volume of the Lapua brass. To zero the rifle, I loaded up a string of rounds using Berger 140 grain Hybrids seated to the lands, CCI 250s, and H4350. Starting at 46.0 grains and ending at 47.5, I fired four groups, all under .5 MOA. With 47.5 grains of H4350 and a Berger 140 grain Hybrid, muzzle velocity reached 2990 fps with a fresh barrel. At the time, I abandoned H4350 and the 140 Hybrids because of powder compression and seating depth issues, but because of a later development they will be included in the next phase of testing.

I need to take a step back and remind everyone that this round was developed as a high-velocity alternative to the 260 Remington, and was designed to be fired from a standard-length detachable magazine. That means that any load development must take into account that the overall length (OAL) of the round must be limited to approximately 2.870” to fit in a magazine such as an Accuracy International AI-3902. That magazine and its 5-round cousin, the AI-3901, are very popular among folks shooting rifles using a DBM platform, so that’s what I was testing for. With H4350 and 140 Hybrids, I had reached the limiting factors of case capacity and seating depth (the bullet tips were dragging on the front plate of the magazine), so I switched powders to one I had never used, Alliant RL-26, and started testing it with the 140 Hybrids.

I ran into the same ceiling with the Hybrids while using RL-26. At 49.5 grains, I was still under 3000 fps and running into a compressed load while seating to the lands. I pushed it up to 50.5 grains with a 12” drop tube, but couldn’t reliably seat the bullets off the lands and clear the magazine. The two bullets I could seat landed in the same hole at 100 yards @ 3030 fps. I backed off to 49.5 grains of RL-26 with the 140 Hybrid at 2940 and loaded the last of the new brass to try at long range. While testing this load at distance, something peculiar happened. I kept having to increase the velocity in my Kestrel Elite to match drops at 800-1200 yards.

A quick check with my MagnetoSpeed chronograph showed the muzzle velocity had increased from 2940 to 3030 fps.

Why? I hadn’t done anything differently. I stopped cleaning the barrel 150 rounds ago. What the hell? After inquiring with a few trusted users of Krieger barrels, I concluded that I was experiencing a common phenomenon found when using cut-rifled barrels—they “speed up” after firing enough rounds through them. In this case, I picked up 90 fps after firing 100 rounds or so. It explained why I wasn’t getting the same results as Shawn, who was using a 24” Hart barrel. He started at 3000+ fps and stayed there. With that settled, I still wanted to see if I could get more velocity, maintain accuracy, and gain some more clearance in the magazine.

With 10 days to go before the PRS match, I sized all of my once-fired brass and broke open a 500-count package of Berger 140 grain VLDs.

Alliant’s RL-26 and Berger’s 140 grain Hunting VLDs provided the winning combination.

The Berger 140 grain Hunting VLD is one of my favorite bullets.

I’ve fired thousands of them through three 260 Remingtons and a 6.5-284 into rocks, steel, deer, antelope, and varmints. They flat out work. Using once-fired annealed brass and 49.5 grains of RL-26, I fired four groups with differing seating depths. The winner, at .010” off the lands, produced 3030 fps and bughole precision. It also gave me a ton of room in the magazine, coming in at an OAL of 2.850”. I took a gamble and loaded every case I had with that recipe. It was magical. The trajectory validation phase was as smooth as they come. The drops matched the solver, which matched the bullet B.C. and velocity. I had perfect conditions for video-proofing and a rock-solid, repeatable zero. For my take on trajectory validation, click HERE.

Here are a couple of videos of long range shooting with the 260 Terminator:

Three-shot group fired with a 140 grain Berger VLD seated .010″ from the lands, and 49.5 grains of RL-26.

Before the PRS match, there was one more important test to perform. We didn’t know how temperature stable RL-26 was so I had to find out.

It was good timing, because our little slice of heaven here in the northern Idaho panhandle was experiencing daytime highs in the 80s. I suspected the match would occur during similar conditions. I loaded one magazine with five rounds and sealed it in a plastic bag before tossing it in the refrigerator. I loaded another mag and placed it outside with direct exposure to the mid-day sun. Not exactly a scientific test, but a realistic one. Two hours later, after confirming an outside ambient temperature of 80 degrees, I fired the cold rounds. A half hour later, I fired the magazine that was baking in the sun. The results were encouraging. It looked like I might have to adjust a little for very cold conditions, but hot-soaking the ammo didn’t seem to affect it. The testing I’ve done lately confirms that.

Five-shot group fired during temperature sensitivity testing of RL-26.

The PRS match went off without a hitch. I fired around 160 rounds in two days, with most stages requiring 12 rounds in two minutes or so.

It’s a tough environment for barrels and a great testing ground for a new cartridge. I had zero malfunctions and had no problem self-spotting impacts. Looking at my data from shooting in a few matches last year with my standard 260 Remington using 140 grain Berger Hybrids, it was clear that the Terminator gave me a huge ballistic advantage. Splitting the corrections between the turret and reticle for multiple targets was much easier, and wind errors were fewer. It certainly didn’t keep the barricades and PRS-style tempo from kicking my ass, but in the hands of a practiced tactical shooter its advantages are obvious. The ROs also appreciated the ease of spotting hits from the hard-hitting 140 grain bullets.

With the match behind me, twice-fired brass soon became three times fired as I returned to the mountains of North Idaho.

With Idaho’s spring bear season in full-swing and ground squirrels peeking out from their winter hibernation, it’s the beginning of shooting season for me. At this time, there are 655 rounds logged through the 260 Terminator. Long range accuracy is impressive, with most of the bullets landing between 450 and 1300 yards.

In the next three weeks or so, all of my brass will be four-times fired and the next phase of testing will begin. In addition to general longevity testing, it will include accuracy testing of bullets in the 130 grain class. Also, I’m going to revisit that H4350/140 grain Berger Hybrid load. With the unexpected velocity increase from a seasoned barrel, I believe that combo has some potential. Look for updates as I continue this project, and don’t forget to subscribe to the website.

For more information on the 260 Terminator, feel free to contact me through Panhandle Precision. For more information about Defensive Edge or having your own 260 Terminator built, contact Shawn Carlock at gunsmith@defensiveedge.net or call 208-687-2659.