High velocity chamberings known for having exceptional accuracy.

[elkaholic]

First, IMO, there is no such thing as a "more accurate" case design/chambering than any other case design/chambering. The biggest factors in accuracy are quality/type of rifle components, quality of smithing and rifle build, and load quality/consistency.

That said, in theory, smaller case and lighter loads are less susceptible to barrel harmonics and this is probably why you see BR shooters with cases like the 6ppc and 6 BR. However, larger and higher BC bullets at higher velocities are less susceptible to environmental conditions. In a no wind situation, the 6 BR "might" out shoot a 300 WSM @ 1000 yds, but in a wind situation, especially variable, the 300 WSM will have the advantage. A lot of factors to consider when you are talking accuracy.

Anecdotal stories of my 257 Wby shoots bug holes, etc., don't mean that on average they all shoot bug holes better than any other rifle.

Next, in my 6-284, 61 gr of RL33 is about 100% capacity with a bullet seated near the bottom of the neck. There is very little room for that case to be improved and I don't see it gaining any more than maybe 3 gr of powder space. IMO, not worth the effort and you will end up shortening the neck which is already not long.

+1.......Rich

 

[IdahoCTD]

The big hang up for me is the barrel. I have been machining Rem takeoff barrels for many of my projects. Saves a ton of money. To shoot the high BC 105 Berger requires a 1 in 8 twist. All 243 takeoffs are 1 in 9 1/4. Plus they are 24" long. There are plenty of 1 in 8 twist sporter weight barrels for sale by outfits like Bartlein but they cost over $300. Considering barrel life the rifle would have to be saved for hunting only. No load development past getting one bullet to shoot.

If you want a wildcat bad enough you do what is necessary to make it happen.

9 1/4 twist barrels will stabilize 105 Amax's. I have a Rem. Varm. barrel I rechambered to 243 AI and I have no problems shooting 105 Amax's. Pushed fast enough I would almost bet the Bergers would stabilize in a 9 1/4 twist too. They aren't much longer than Amax's. The Amax is likely the only bullet that will hold together at the super high velocities of the 6WSM, 6 MachIV, etc too.

 

[AZShooter]

IdahoCTD,

I have heard that the 105 a-max are working in a factory rem barrel. Most of us have some elevation on our side which helps with a minimal twist rifle. I may do this chambering yet.

 

[Max Heat]

Can the 6-264 (aka mach4, aka incinerator) be loaded for high accuracy? My solution to throat erosion is to moly coat the bullets and the bore. And starting out with an extra-long barrel, just chop 1/2" off the back end and re-cut the chamber, every time accuracy starts taking a dive due to throat erosion. I'm thinking that'll add around 10X round life to the barrel.

It'll be a while (year or more) until anything starts happening with the next build, as I just recently completed my current one (7RUM). And there have only been 16 rounds through it so far. That does give me time to find some 240I brass and dies. Now that THAT's settled, I plan on going large on the next build after that. I will likely be going 338 bore, also with a large-volume chamber behind it, of course.

 

[AZShooter]

Based on what I am seeing with my bore scope setback results might work might not. I did read this positive note and kept it in my 6mm-284 documents:

"I do my own barrel work so changing out a barrel or setting one back that has throat wash is not a problem. I usually set a barrel back the length of the barrel tendon at around 1000 to 1200 rds, sometimes before, sometimes after - just depends on what it's accuracy is doing.
Each rifle has a different barrel on it so I am not biased on any particular barrel manufacturer. One wears a Hart, one a Krieger, one a Broughton, and one has a Bartlein. All shoot with excellent accuracy and very fast.
I also shoot moly in all my rifles and I feel that it does get me an extra 100 to 200 rounds out of the barrels.
I also keep and eye on the throat erosion with my Hawkeye borescope and it helps me determine if erosion may be causing a accuracy problem and/or if it's time to rechamber or rebarrel."

-------------------

I have read that some bench rest guys will setback ONCE with a shorter barrel life on second rechambering.

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The 28" 6mm-284 has crazing going out for over 8". There are also longitudinal cracks that are longer looking like a fissure that happens in the earth with an earthquake. Gun still shoots at 900 rounds but cleanup is very tedious.

I think the 6mm-284 really is the largest cartridge to make a serious rifle. The Mach IV is too radical unless you have deep pockets or only intend to shoot it at big game.

-----------
I have a 257 weatherby with a 3 groove barrel that began to chew up Berger 115s at round count 450. ( I suggest you stay away from a 3 groove) Had to move to the accubond but lost the valuable BC. Still shoots at round count 800 but talk about ugly fissures/crazing!!! Way way up the barrel over a foot. Clean up takes a few days of soaking with bore tech eliminator. I am too busy to sit there pushing patches till it cleans up.

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I did a search for brass today. It may just take you a year to find what you need! Did find some norma 7 rem mag brass but no other brass that could make a mach IV.

 

[IdahoCTD]

Can the 6-264 (aka mach4, aka incinerator) be loaded for high accuracy? My solution to throat erosion is to moly coat the bullets and the bore. And starting out with an extra-long barrel, just chop 1/2" off the back end and re-cut the chamber, every time accuracy starts taking a dive due to throat erosion. I'm thinking that'll add around 10X round life to the barrel.

It'll be a while (year or more) until anything starts happening with the next build, as I just recently completed my current one (7RUM). And there have only been 16 rounds through it so far. That does give me time to find some 240I brass and dies. Now that THAT's settled, I plan on going large on the next build after that. I will likely be going 338 bore, also with a large-volume chamber behind it, of course.

1/2" isn't going to clean up much when the accuracy starts to fall off. Most likely you'll need to start with the 30" barrel with a 5-6" flat at the chamber and cut 3-4" off. The second go only seems to get about 50% more barrel life before it is totally done. If it was me I'd either have 2 barrels chambered at the same time or nitride the one barrel and hope for the best.

 

[Max Heat]

Ok, looks like my 1/2" idea was WAY off-base. I don't [yet] own a borescope, and I haven't put enough rounds through any given barrel yet to burn it out. Obviously I had NO idea what I was talking about. I would NOT be thrilled about having to reduce a 32" barrel down to 26", and only see 50% more rounds out of it, to boot. I've never done 3-groove, either. I have heard of barrels that have chromed out bores, but never a titanium nitride coating. I wonder how well it would work to extend throat life, if only used in conjunction with moly-coated bullets.

Rem brand 7RM brass not any good for forming incinerator cases? I have lots of those to work with.

Maybe 6-264 IS too "obscure" for me to want to mess with. But I'm going to [hereby] declare that NO chambering [within SAFE limits] will EVER be too radical for ME!

Since I already have a 7, my goal is a below 7 build (6.5/6.8 is too close), then an above 7 build (30cal is too close). And I ALWAYS "like to, anyways" go with the maximum chambering. I already bought a [used] set of 220S dies, thinking that was where I would be going on the small-cal build. But what I'm not so thrilled with, is the long-range wind-bucking capabilities of .22 (.224) caliber. But at least brass is readily available, and the chamber is a standard option when getting a barrel.

For the big-cal, I'm figuring on 338. But I want chambering that uses at least a 500J-based case, built on an extra-large (or whatever the correct name is) action. Capacity would have to be like 150-160gr minimum. I have yet to find any "standard" case offering, that fulfills THAT requirement. But what is the highest that the "readily available" [non-custom order] WC's go, on a .338 bore?

 

[AZShooter]

I know you could neck down 7 rem mag brass to 6mm. Might not be one step. A 264 win mag seater die would get it part way. Then the FL die with the sizer ball removed would be a little more. Finalized neck down might be done with a bushing die IF you were able to chamfer the neck edge or bump just the neck a tiny bit with a 25 cal or 6mm die so it would slide into the 6mm-264 bushing.

I mentioned using the reamer and a die blank to make a form die. Some extra sanding polishing of this die would allow you to go from 7mm down to 6mm then finish with your bushing die.


Don't know what you mean by: the WC? "readily available" [non-custom order] WC's go, on a .338 bore?"

 

[Max Heat]

I know you could neck down 7 rem mag brass to 6mm. Might not be one step. A 264 win mag seater die would get it part way. Then the FL die with the sizer ball removed would be a little more. Finalized neck down might be done with a bushing die IF you were able to chamfer the neck edge or bump just the neck a tiny bit with a 25 cal or 6mm die so it would slide into the 6mm-264 bushing.

I mentioned using the reamer and a die blank to make a form die. Some extra sanding polishing of this die would allow you to go from 7mm down to 6mm then finish with your bushing die.


Don't know what you mean by: the WC? "readily available" [non-custom order] WC's go, on a .338 bore?"

Sorry, WC was short for "wildcat". I was asking about available right off the shelf (already made), without "special" order.. That sentence was referring to the 338 build, which will come AFTER the 6mm build, but it does apply equally to the 6 build.

Some of the more popular wildcat dies [and brass] are "off-the-shelf" available, aren't they not?

Would the reamer that you speak of also be required for chambering the barrel, or can the barrel be ordered already having the proper chamber?

Why isn't it just called the 6mm Remington Magnum?

 

[AZShooter]

Max heat,

PM sent

 

[Jud96]

Sorry, WC was short for "wildcat". I was asking about available right off the shelf (already made), without "special" order.. That sentence was referring to the 338 build, which will come AFTER the 6mm build, but it does apply equally to the 6 build.

Some of the more popular wildcat dies [and brass] are "off-the-shelf" available, aren't they not?

Would the reamer that you speak of also be required for chambering the barrel, or can the barrel be ordered already having the proper chamber?

Why isn't it just called the 6mm Remington Magnum?

The 6.5 Remington Mag necked down to 6mm is called the 6mm Remington Mag.

 

[Max Heat]

The 6.5 Remington Mag necked down to 6mm is called the 6mm Remington Mag.

But then THAT begs the question: Is the 6.5 rem mag based on a necked-down 7RM cartridge?

I tend to think the answer would be no. But as of right now, I have not "researched" it. If it was, the 6mm Remington mag would, for all intents and puroses, BE the 6-264/mach4/incinerator, right?

I think it might be time to start summarizing now.

I know some say caliber makes no difference in accuracy. But if you do buy into the idea that it does, 5.56-6.5/6.8mm seems to be where it's at (up tp 1000yd), going by the BR guys. I do like 5.56, but it fades out past 300yd. As previously stated, I already have a set of swift dies on hand, plus brass & barrel chambering for swift is commonly available, without any special ordering. That looks like what I will end up falling back onto, if I can't come up with a 6mm/.243 cartridge that is hot enough to do 3750fps out of a 30" barrel, without getting into special orders/obscurity.

 

[MontanaRifleman]

But then THAT begs the question: Is the 6.5 rem mag based on a necked-down 7RM cartridge?

I tend to think the answer would be no. But as of right now, I have not "researched" it. If it was, the 6mm Remington mag would, for all intents and puroses, BE the 6-264/mach4/incinerator, right?

I think it might be time to start summarizing now.

I know some say caliber makes no difference in accuracy. But if you do buy into the idea that it does, 5.56-6.5/6.8mm seems to be where it's at (up tp 1000yd), going by the BR guys. I do like 5.56, but it fades out past 300yd. As previously stated, I already have a set of swift dies on hand, plus brass & barrel chambering for swift is commonly available, without any special ordering. That looks like what I will end up falling back onto, if I can't come up with a 6mm/.243 cartridge that is hot enough to do 3750fps out of a 30" barrel, without getting into special orders/obscurity.

Most, if not all the belted mags are based off the 375 H&H, which is the only belted case in which thhe belt actually serves a purpose. And that purpose is to headspace off of.

The 6.5 Rem Mag was actually based off the 350 Rem Mag. The larger 264 Win Mag is the necked down version of the 7 Rem Mag. Exact same dimensions. The 6.5 RM is a good bit shorter than the 264 WM with a slightly steeper taper. Case capacity diff is 69.3 vs 80.7

 

[Jud96]

Most, if not all the belted mags are based off the 375 H&H, which is the only belted case in which thhe belt actually serves a purpose. And that purpose is to headspace off of.

The 6.5 Rem Mag was actually based off the 350 Rem Mag. The larger 264 Win Mag is the necked down version of the 7 Rem Mag. Exact same dimensions. The 6.5 RM is a good bit shorter than the 264 WM with a slightly steeper taper. Case capacity diff is 69.3 vs 80.7

+1 MontanaRifleman said it like I would have. Basically the 6.5 RM is the short mag version of the .264 Winchester.