Intrigued by truly big 6mms - and their absence in the shooting world

[Calvin45]

If I ever get into wildcatting and custom to semi-custom builds one of my first pursuits will be a "big 6" of some kind. 6mm-06, 6-06ai, 240 Gibbs, 6-6.5 rpm, .240 incinerator/6mm Mach 4 (7mm rem mag parent), 6mm wsm, 6-6.5 prc....lots of possibilities. Something bigger than a .240 wby or 6-284.
It seems like this is conspicuously among the only bore diameters that don't have any truly "stupidly overbore" representatives emerging among commercial offerings. (Give the Wikipedia article on the .244 hh magnum a read, a hotrod before
Hot rods were cool).
Why is that? What do you think?
Also, am I alone in thinking, practicality be left behind, a 6mm-6.5 weatherby rpm is especially intriguing?

 

[Deleted member 103481]

With cartridges like the 26 nosler and the 6.5-300 wby many people are already unwilling to drop down into that much of a burner for bullet weights that commonly are considered marginal for elk/moose sized game.

A 6 burner makes that problem even worse, as not only do most discourage their use on large game, but many states don't even allow it. Now you're left with a long range antelope cartridge, that will burn out in what 600 rounds?Further, even the best, longest, sexiest 6mm bullets on the market have a BC less than an average 6.5mm offering.

That's what I think, for the little that's worth lol

 

[Stiltsville]

Built a 6mm (not .240) 244 H&H a few years back with 26" bbl on a 700 Magnum action. It was a rocket ship and few bullets could survive it. The Barnes 6mm could and it was a deadly killer.

Sold it on to an Australian for "Roo" hunting.

 

[Calvin45]

With cartridges like the 26 nosler and the 6.5-300 wby many people are already unwilling to drop down into that much of a burner for bullet weights that commonly are considered marginal for elk/moose sized game.

A 6 burner makes that problem even worse, as not only do most discourage their use on large game, but many states don't even allow it. Now you're left with a long range antelope cartridge, that will burn out in what 600 rounds?Further, even the best, longest, sexiest 6mm bullets on the market have a BC less than an average 6.5mm offering.

That's what I think, for the little that's worth lol

Sensible thoughts. The counter argument that might be made is that in many places the 6mm is the minimum legal caliber for big game hunting. Seems the big 22s are quite popular and the big 6.5s as you've stated, so I'm at a bit of a loss as to what's up with the 6mm bore.

 

[Deleted member 103481]

Sensible thoughts. The counter argument that might be made is that in many places the 6mm is the minimum legal caliber for big game hunting. Seems the big 22s are quite popular and the big 6.5s as you've stated, so I'm at a bit of a loss as to what's up with the 6mm bore.

Yeah that would make sense. I think the 22 hot rods are varminters? Maybe they only want to blow up the woodchucks so much?

I big bad 6 would be a kick butt long range yote cartridge

 

[Stiltsville]

Two facts that seem to be invisible:
1. Barrels are cheap.
2. Nitriding triples barrel life.

 

[Calvin45]

Two facts that seem to be invisible:
1. Barrels are cheap.
2. Nitriding triples barrel life.

No experience with nitriding but am starting to gain experience treating bullets and barrels with hexagonal boron nitride. Not sure how that compares but the tests of others sure do indicate prolonged barrel life. That combined with modern powders that erase copper fouling, so problematic with small bore hot rods in the past, and I agree with you fully here. It's a non issue to my mind. Wanting a high performance cartridge and then worrying about barrel life is kind of like guys buying huge trucks and complaining/asking how it does on gas mileage.

 

[Stiltsville]

Right you are.

 

[AZShooter]

I made a 6mm-264 win mag. Had the 7 Rem mag reamer ground to 6mm. Rechambered a 26" 243 Rem takeoff. Used necked down 264 win mag brass.
I already had a 6mm-284 in a heavy 30 barreled package shooting 105 Bergers at just under 3500 fps.

Had a Rem LA and wanted to make a sporter package I could use for hunting deer or antelope. It didn't work out so well. Due to twist I had to use a shorter bullet. Chose the 95 gr Berger. Worked up to 3650 fps. Accuracy came and went. The issue was perhaps the use of a rough factory barrel. The amount of powder burned in the barrel would cause fouling quickly as I was working up a load. I used CO2 to keep things cool. The fouling with less than a dozen shots would cause the groups to get larger fast. Never felt I could use it as consistency would change with so few rounds through the barrel.

FYI I made a 24" sporter 6mm-284 with another 243 Rem takeoff. Got 3465 fps with 95 gr Berger. Difference was consistent accuracy past 20 rounds.

Ross Seyfried wrote an article on his version the Mach IV. First barrel had to be thrown away due to a hard carbon ceramic like substance building up on the first barrel due to not cleaning it every dozen rounds or so.

He stated that he could get 4205 fps with IMR 7828 and 70 grain nosler BT and 4150 fps with 75 grain x bullet. IIRC this article was back in the 1990s.

Would love to read about it if you attempt using a larger case than a 6mm-284. Let us know how it works out for you.

 

[Quintus]

I love the .240Wby with Partitions or TSXs and 70 b-tips for the non-edibles. I think a 6mm X 6.5Prc would be the cats 6.

 

[highdrum]

A 6prc and 6x284 and 6-06 are all basically the same case @ 70gr. 6saum 6-06ai step up by about 3-4gr. 6wsm would be about 77gr. Everything else would be over 80 and way overbore. Anything over mid 70gr will just be more heat and loss of more barrel life. I would look at a 6 sst Sherman case, it's already been built.

 

[Stiltsville]

My 244 H&H w/27" bbl pushed the 80 gr TTSX @3750 fps. A death ray.

 

[Gibbshooter43]

I shot my first big six; a 240 Gibbs, almost 40 years ago. It was owned by a man who became a life long friend and shooting buddy / reloading mentor. I was hooked. Not having the funds to do a custom build, I looked for years to find a good used one. I made do with AI'ing my 243 and a couple years ago finally located the 240 Gibbs I'd be searching for. Built on a Mauser action with a 26" Shilen barrel, it's already accounted for two very nice Idaho whitetails, one of which is in my avatar.

 

[DJ Fergus]

Sensible thoughts. The counter argument that might be made is that in many places the 6mm is the minimum legal caliber for big game hunting. Seems the big 22s are quite popular and the big 6.5s as you've stated, so I'm at a bit of a loss as to what's up with the 6mm bore.

I have a good friend with a 6mm-06. I contemplated a 6mm-284. I have a 25-06, 6.5 creedmoors and various larger calibers. I rolled all these ideas around in my head and I came up with this: I could build a 22 caliber to run bullets that matched the highest b.c. of the 6mm bullets and run them just about as fast in a creedmoor capacity case as I could run bullets of the same b.c. 6mm bullets in an 06 or 284 case with less recoil. I went with a 22 creedmoor. Now granted, I don't have as much ft/lbs energy but wind tradjectory and bullet drop are near identical. All this being said, I would still love to have a 6mm-284. It's just a little farther down the list of my wants than it used to be.