I already did all that testing with the 3 twist when they first came out from Faxon.
The barrel is off the gun for a fairly long time and I will never go back to the 3 twist.
Barrel quality from Faxon was horrendous, when they brought out the first 3T huge pits, torn & galled rifling.
Your barrel may be of better quality hopefully, maybe they learned how to do the 3T better.
I have purchased a Faxon 450 bushmaster barrel twice because the first was bad rifling and inaccurate, the 2nd was a little better.
I will not recommend their barrels or the limited 3 T barrel.
Hornady is running an 8T on their 338 ARC...ever wonder why?
They have deep pockets and lots of testing equipment, plus bullet manufacturers to find the best combination.
I run the 6.5 twist, now on my 8.6 Blk after wasting countless dollars and time shooting the 3T...trying to make it work.
Damaging my muzzle devices, the magneto speed bayonet, working with the 3T and found it inaccurate and dangerous with lead jacketed bullets.
None of that occurs with tbe 6.5 twist, accuracy, much higher super velocities, and the total use of All bullets at their max velocities, the 3T does not measure up for versatility.
A 24" bolt gun I run cheap jacketed 200 gr Speer hot core at 2600 fps, 160 gr Barnes TTSX to 2800 fps, 300 gr Berger at 1943 fps, 350 gr Maker limited to 1000 fps by manufacturer in 3T runs ...but runs 1675 fps in 6.5 twist...as a few examples, why I do not recommend the 3 twist to anyone...I've been there done that.
But if you like yours keep shooting it and thanks for the effort in load development for the 3T, but I've already done that, and moved on.
H335 is a good powder for the 8.6 Blk in both twists but just like my earlier testing, you also confirmed the 3T can not match the super velocities of the 6.5 twist by hundreds of feet per second in most cases, and not even close with lead jacketed bullets or speed limited Maker subs like 1050 fps 3T vs 1675 fps 6.5 T with 350 grs.
That alone plus the accuracy increase is why my experience, with both twist rates, tells me to push people away from the 3 T.
For subs only, for me, I've shooting the 338 Spectre, while waiting on tbe 338 ARC reamer, for some time in tbe AR 15.
The tiny 338 Spectre has been very accurate, & very consistent, single digit velocity S/Ds plus a lighter AR 15 platform, with its 6.5 T barrel shooting everything from 160 Barnes to 350 gr Maker.
The 350 gr is a lot of bullet for this tiny case and Maker makes a 300 gr that's better suited and specifically made for it plus their Super Expanding 165 gr at 2100 fps might give one extra desired range.
Plus Hornady the the very similar 338 ARC coming one of these days, I already have the cases.
This should be a very accurate sub gun for the light AR platform and short barrels.
They are 8 twist barels with their two loads a 307 gr sub, which should expand at sub velocities, can also be utilized in the 338 Spectre, 6.5 T. But the 3 T, who knows?
Hornady engineers laughed at the ridiculous 3 T on video, and went with 8 T, which highly irritated "one" person.
After spending a ton of time and money on the 338 sub/ super combo, it's not easy to do both with the best outcome of either...but the 6.5 twist is a huge plus.
I believe the best subs, are the small capacity cases, like the 338 ARC or 338 Spectre are the way to go for subsonic shooting.
The 338 Spectre that I have in AR 15 is an absolute blast, super accurate, shoot the eye out of a hog at 75 yards all ten rds.
I expect the same from the 338 ARC.
But neither is much of a super cartridge.
The 165 gr at 2100 fps that's supposed to expand at 900 fps may be the LR bullet for these tiny cases.
Thanks for sharing your experiences, it was actually your earlier posts that were the basis of the loads that I'm working on right now. It’s clear you’ve done a ton of work testing both the 3T and 6.5T setups, and I respect the effort you’ve put in to get the best performance. I agree that the 1:3 twist is a niche chambering—it doesn’t match the versatility of the 6.5T for supers or lighter bullets. That said, it offers unique advantages for specific use cases like heavy subsonic and monolithic bullets where stabilization and terminal performance matter more than outright velocity.
I also wanted to point out that in my testing, I hit 2600 FPS with a 160-grain Barnes TTSX out of my 16-inch barrel. That matches the velocities you mentioned of 2800 fps for your 24-inch barrel after adjusting for barrel length, see the calculator screenshots (velocity on the far right).
This shows that the 1:3 twist can be used to achieve sufficient supersonic velocities. Additionally, I want to address a common misconception that I see with 8.6 BLK and fast twist in general. Fast twist isn’t inherently slower—it’s just redistributing some of the forward energy into rotational energy.
One factor contributing to the velocity difference we observe is bullet weight. Heavier bullets, like a 225-grain compared to a 160-grain, as we know, require significantly more force to accelerate. In a 1:3 twist barrel, this difference is amplified because of the increased torque needed to spin the heavier bullet against the sharper rifling. The torque required to spin a bullet scales with its rotational inertia, which depends on both its mass and radius: Torque ∝ Mass × Radius². A 225-grain bullet has about 40% more mass than a 160-grain bullet, resulting in a significant increase in torque requirements to spin the bullet at that twist rate. In a fast twist barrel like 1:3, some of the energy is diverted to overcome this increased torque demand, which lowers forward velocity. However, this energy is not entirely wasted—a lot of it is converted into rotational energy (I'm not a Q-Fan Boy, but their marketing is still based in science). There’s a common misconception that the 1:3 twist wastes a significant amount energy compared to a slower twist like the 1:6.5. That’s not quite true—the total energy of the bullet should similar in either twist rate (slightly slower in 1:3 as there is more friction), but the energy is split differently. In a faster twist barrel, velocity (and forward kinetic energy) is slightly reduced because some of this energy is diverted to rotational energy: E_total = E_kinetic + E_rotational. Whether or not the rotational energy has an advantage is still up for debate, and we can all draw our own conclusions on that. What I believe happens, however, is that when those heavier projectiles are traveling down the barrel in a fast twist, they hit a wall in torque requirement. I think the pressure generated in standard cartridges (60k-ish PSI) pushing the bullet cannot overcome this rising rotational inertia requirement, and thus you see marginal fps gains past a certain point in these heavy projectiles. I don't think this is as big of an issue in lighter projectiles, as evidenced by the performance I was able to achieve today with the 160 Barnes TTSX. That 40% more mass causes a huge spike in rotational energy demands throughout the entire acceleration of the bullet. So in my opinion, in 1:3 twist, lighter is better for super sonic if your goal is velocity.
Rotational Energy:
E_rotational = (1/2) * I * ω²
Where:
- I = (1/2) * m * r² (moment of inertia for a cylinder-shaped bullet)
- m = mass of the bullet (in kilograms)
- r = radius of the bullet (in meters)
- ω = (2 * π * RPM) / 60 (angular velocity in radians per second)
I also wanted to address the definition of versatility because I think we’re approaching it from different angles. You’re talking about versatility in terms of potential load combinations and how the platform can be optimized for velocity and accuracy from a reloading/gunsmithing perspective. For me, versatility is about the cartridge’s application in the field—short barrel, under 300 yards, and the ability to run both supersonic ammunition and heavy subsonic loads. From a pure hunting perspective, that’s where I see the 8.6 BLK shine. I might be out in the woods and make game time decisions and choose to hunt a close range sit of 50-75 yards, or depending on the conditions/movement of game, I might need to stretch the rifle out to 200 yards. I don't want to carry two different guns depending on the conditions for the day, but two different types of ammunition is perfectly fine by me. To me, that's what versatility is, being able to do what I just described, out of a highly maneuverable, short barrel weapon, with a suppressor.
For any other application outside of hunting, I'm not sure why to even bother with 8.6 BLK, outside of just experimenting and having fun.
I do think that your 1:3 barrel from Faxon was a bad one. I’ve seen reports of quality control issues early on, but my FX-7 was manufactured in October, and has been nothing but flawless. I had my gunsmith who builds precision rifles for competition inspect the barrel, and he said "yeah it's pretty okay", which by my standards means it's probably pretty nice. (He didn't like the tooling marks on the action, for those who are considering buying an FX7, it shoots fine though). I think they’ve refined their manufacturing since the earlier production runs.
Finally, I am curious—why did you choose a 24-inch barrel for 8.6 BLK? It’s great to see what you’ve achieved, but with that length, I'm not sure where the desire to have subsonic capability comes in with a barrel that long. And if there is no sub-sonic desire, then why not just use .338 Federal instead of 8.6 BLK? Was it for experimentation or were you targeting specific performance goals?
I feel as though we agree that there are better cartridges for specific use cases. I plan on adding a .338 Arc to my arsenal for pure sub-sonic use. But that isn't what I got the 8.6 BLK for. I got it to do either subsonic or supersonic, at a moments notice, when the duty calls. And as far as I am aware, that was the original goal and vision behind the cartridge.
I appreciate the dialogue—it’s great to hear from someone who’s done extensive testing with both twists. While I’m sticking with the 1:3 for my specific use case, which again is hunting under 300 yards, out of tree stands and blinds, where the guns overall length with a suppressor is critical for maneuverability, and a few bucks more on monolothic ammo doesn't mean much in the grand scheme of hunting. I completely understand why others might prefer the 1:6.5 for its versatility in load development. At the end of the day, it’s about matching the outcomes to your goals.
Will change out to 1:6.5 tw down the road if I start hitting a wall with my satisfaction. But I doubt I will, part of the fun is seeing how much performance you can get out of what you have, right? To answer your question about why I went for 1:3, the answer is, "to have fun" 
