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Old March 5, 2014, 07:45 PM   #1
Eppie
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I would like a Hot Rod 6mm.....so which one?

I've started to focus more on target and competitions for extreme distance and extreme accuracy. I have a good .308 but I've begun lusting after those hot rod 6mm. I do reload, but with so many choices I feel like a kid in a candy store that can only have one.

My first rifle wan an M-16, so I'm very partial to box magazines. The big constraint is that the loaded cartridge may not exceed 2.95" in length.

So which one???

Please help me decide.
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Old March 5, 2014, 09:24 PM   #2
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About as "hotrod" as is practical is the 6mm06 or 240 Wby. Any more powder space is an inefficient barrel burner.
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Old March 5, 2014, 09:33 PM   #3
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6x284 is as hot as you can get and maintain any barrel life, though not much. I had one and on last re-barrel it became a 6BRNorma.
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Old March 5, 2014, 09:34 PM   #4
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Neck down a .338 lapua to .243

But seriously a 6mm-06 would be cool. The cartridge should push high BC bullets to high velocities. 105 grains to 3200+fps. That's actually slightly faster than what I'm seeing for the .240 weatherby (which will push a 100 grain bullet about the same speed) you could probably stretch it even more, with a Akley improved case and chamber, if you wanted/needed to.
The cases are fairly similar, if I'm not mistaken, close enough to form both from 25-06 brass, from what I'm told.
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Old March 5, 2014, 10:01 PM   #5
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Barrel life for a tack drivin' 6x.284 (one that shoots no worse than 1/4 MOA at 100 yards) will be about 400 to 500 rounds. The 6.5x.284 barrel life in match rifles shooting that well have a barrel life of 700 to 800 rounds. I think a 6x30-06 would be about the same.
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Old March 5, 2014, 10:05 PM   #6
Eppie
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Thanks for the response guys. I should have included more info, My first rifle wan an M-16, so I'm very partial to box magazines.

The big constraint is that the loaded cartridge may not exceed 2.95" in length. My apologies I will correct the opening post

Quote:
reynolds357 said: 6x284 is as hot as you can get and maintain any barrel life, though not much. I had one and on last re-barrel it became a 6BRNorma.
Good one, that is a hot number no doubt. But, there is no way I can get that in a box magazine.

Quote:
JD0x0 said: Neck down a .338 lapua to .243
If I ever wanted to see a bullet tear itself apart that a sure way to do it.

Quote:
But seriously a 6mm-06 would be cool. The cartridge should push high BC bullets to high velocities. 105 grains to 3200+fps. ....you could probably stretch it even more, with a Ackley improved case and chamber, if you wanted/needed to.
I think .243 AI is a little too long to fit in a mag also.

Here's what I was comparing. What am I missing?



The 6.5 are there instead of the 6mm. Ammoguide didn't have those cartridge to represent.
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File Type: jpg Comparison 11.JPG (144.0 KB, 174 views)
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Old March 5, 2014, 10:30 PM   #7
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go with a 6mm Remington and be done with it.
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Old March 5, 2014, 10:39 PM   #8
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Pathfinder is likely right in his suggestion. I just read a good article by a fellow that ordered a 6.5-284 for testing and was sent a 6-284 by mistake. Since that was what he had, he wrung it out pretty well and found that the muzzle velocities were no better than the 6mm. Still, logic dictates that more powder (to a point) will generate more MV, so there may be a bit of advantage to the 6-284, but probably not much.

Why not go with a 6.5mm instead?
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Old March 5, 2014, 10:43 PM   #9
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I have a 6mm Rem, and given my experience with it as well as your stated parameters, it would be my choice.
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Old March 5, 2014, 10:44 PM   #10
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You can do can do 6x284 in box magazine

they did this 284 in a Badger magazine.

http://www.6mmbr.com/gunweek095.html
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Old March 5, 2014, 11:30 PM   #11
Eppie
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Ok Guys,
You're right a 6 x 284 works in a short action. But here's what Sierra's manual says, you need to read it yourself or you wont believe me.



So we need to move past the 6 x 284 and the 6-06. The 6.5 x 284 maybe king but the 6 x 284 is a bit too rich and finicky for my liking.
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Old March 6, 2014, 01:45 AM   #12
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Have you considered a 243 WSSM?
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Old March 6, 2014, 08:51 AM   #13
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Quote:
Scorch said: Have you considered a 243 WSSM?
That one escaped me, it's not listed in the Sierra manual, but I found it in the Nosler book.

The thing that jumps at me is that with a .535 bolt face, if I'm not happy with it I'm sort going to be very limited in choice of calibers to rebarrel. The other thing is that when you get into the 105-115 grain bullets the velocity comes right back to 3,000 fps. So there isn't much gained, if anything over the .437 bolt face cases.

I guess I should include the 105 Berger hybrid as basic criteria. That's what I'm planning on using.
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Old March 6, 2014, 02:32 PM   #14
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Eppie, Since you already figured out which bullets/velocity why don't you call Sierra get their advise.
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Old March 6, 2014, 02:41 PM   #15
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I would go with the 6mm Creedmoor (not a 6mm CM which is the 6mm Competition/Match),6mm XC, or 6x47 (the 6x47 has a small rifle primer). All three of these are shorter than the .243 Win. which is based of the .308. Their shortness would allow you better bullet seating in your magazines.

There is also the 6.5 RSAUM 4S which is talked about extensively at Sniper's Hide.

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Old March 6, 2014, 03:33 PM   #16
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Eppie,

You could ask Brian Pflueger how his 243 AI build worked for him.

Based on your responses so far I think that the 243 AI is where you are heading.

But if you build on a Savage action, you can swap bolt heads and use a 243 WSSM, and get the same velocities as the 243 AI.

Or you can get a 243 WSSM upper from Oly Arms, and if you want to rebuild it into something different later, swap barrel and bolt.

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Old March 7, 2014, 05:03 PM   #17
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Quote:
Jimro said: Eppie, You could ask Brian Pflueger how his 243 AI build worked for him. Based on your responses so far I think that the 243 AI is where you are heading.
Hi Jimro,
I've agonized over the 243AI, or the 6CM (Competition Match), however according to the bulletsmiths at Sierra (see above) the 6 x 284 reached the point of diminishing returns, so the 243AI having even larger capacity should suffers from the same problem.



I think the choice comes down to the 6CM or the 243 Improved 30degree. The difference between the two is 1 degree shoulder angle. That's pretty irrelevant. I'm leaning to 6CM (Competition Match) because it's easier to say than ".243 improved 30degree".

In the final analysis the .243 can only be improved by changing the shoulder angle so that brass last longer and powder so that the barrel last longer. Of course if you're a company selling rifles and ammo neither of those two is a consideration when designing a case.

I wonder how long before someone comes out with a ".308 improved 30degree"
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Old March 7, 2014, 08:06 PM   #18
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Eppie,

All overbore rounds have reached the "point of diminishing returns" but that doesn't stop them from actually having performance gains as compared to other rounds.

Compare the 280 Rem, 7mm Rem Mag, and 7mm RUM. The most efficient case is has the least capacity, and as you get bigger cases you have to get substantially bigger to get better performance (if you are operating in the same pressure ranges as these three are).

The 243 Win is already maxed on pressure, so case capacity must be increased to increase performance. But you don't get enough case capacity increase from the AI process to get a serious jump in performance (although there will be an increase).

Your particular set of requirements, 6mm and short action, are a bit peculiar but they are what they are. You could neck down a 270 WSM to 6mm and stuff it full of some ultra slow ball powder like WC872 under a 115gr DTAC and jump up farther in the point of diminishing returns to gain extra velocity over 3k fps.

You would probably only get about 800 to 1000 rounds before accuracy was degraded due to your bore getting burnt up and sand blasted by powder, but you could do it.

It's all in what you decide you need from a ballistic standpoint. For what it is worth the standard 243 Win does just fine in the long range department.

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Old March 7, 2014, 08:21 PM   #19
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Jimro, here's what I've been chewing on. I'd like your opinion.
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Old March 7, 2014, 08:50 PM   #20
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I haven't read that entire paper but I'd be most curious why the .243AI doesn't meet their criteria.

They want 3,000fps with either 107 or 115gr bullet and suggest N167, N170 or H1000.

With a 24" barrel, QuickLoad says the .243AI can do 3,000 with the 107 or 115 using H1000 and not exceed 60k psi. QL doesn't have N167 and N170 is much too slow, even a 110% compressed charge doesn't reach 3,000.

There can't be that much difference between them. Here a pic of them side by side, and they're both made by fireforming a .243Win case.

http://forum.accurateshooter.com/ind...h=880906;image
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Old March 8, 2014, 12:17 AM   #21
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Hi Brian,
You have to remember that they are thinking from an XTC perspective and the rapid fire requirements of 10 shot strings.

I believe their main issue with the .243AI is the overall length. It's too long to fit in the mags.

The difference between the .243 and 6CM is that the 6CM holds 2 more grains of water. Another thing I found out is that most people shooting 6CM use a 28" barrel to get those velocities.
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Old March 8, 2014, 01:18 AM   #22
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Eppie, I suspect you're thinking of 6mm Remington AI, when referring to .243 AI (.243 Winchester Ackley Improved).
The actual .243 AI runs the same basic OAL as .243 Win, and works with any 'standard' short action. The 6mm AI, however, is based on the 7x57mm case, which is notably longer (and requires an intermediate or long action).


And, don't let barrel length get into your head, too much. The bore and groove finish will have more impact on velocity than the actual length.

I have owned a 22" and a 25.5" .243 Winchester.
One of my brothers owns 18" and 22" .243 Winchesters.
And, my father just jumped on the bandwagon with a 24" .243 Win.
We have all shot the same Remington 100 gr factory load, as well as a Federal 100 gr load, and a Winchester 100 gr load. The difference between the barrel lengths only differs 33 to 140 fps. With a difference of 7.5" .... only 33-140 fps.
And with handloaded Hornady 95 gr SSTs on top of IMR 4064?... 40 fps.

Unless you drop some serious change for a high end barrel, or have someone hand-lap a decent quality barrel, anything over 20" is a crapshoot. It might get you a little more velocity ... or it might not.
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Old March 8, 2014, 01:31 AM   #23
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Quote:
Hi Brian,
You have to remember that they are thinking from an XTC perspective and the rapid fire requirements of 10 shot strings.

I believe their main issue with the .243AI is the overall length. It's too long to fit in the mags.

The difference between the .243 and 6CM is that the 6CM holds 2 more grains of water. Another thing I found out is that most people shooting 6CM use a 28" barrel to get those velocities.
You're definitely confusing the .243AI and the 6mm Rem AI.

The .243AI and the 6mm CM are both formed from standard .243Win cases and according to the diagram up above, the CM has less shoulder angle. It's case capacity should be between the .243Win and .243AI.

Besides, 2gr is nothing. You can gain or lose 2gr of water capacity just by switching brands of cases.
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Old March 8, 2014, 09:56 AM   #24
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Quote:
Brian Pfleuger said: You're definitely confusing the .243AI and the 6mm Rem AI.
Quote:
FrankenMauser said: Eppie, I suspect you're thinking of 6mm Remington AI, when referring to .243 AI (.243 Winchester Ackley Improved).
The actual .243 AI runs the same basic OAL as .243 Win, and works with any 'standard' short action. The 6mm AI, however, is based on the 7x57mm case, which is notably longer (and requires an intermediate or long action).
You're both right. My apologies, somewhere along the way I went off the rails. A good night sleep restores balance.

Brian and Frankenmauser, all your comments are right on the money. The plain .243, the .243AI, the 6CM and the .243 Improved 30 degree are all from the same case, same length. The difference is only is shoulder angle. The 6SLR is from the same case, but the shoulder is slightly lower than the .243 Improved 30 degree so that it can have a longer neck.

It's all very interesting and can be confusing. I think there is some merit over the shoulder angle, but whether it is 30, 31 or 40 degrees will probably never be determined conclusively.

Certainly buying dies is much more straight forward with the .243AI than any of the others. But, as I learned in my old marketing classes, a catchy name can make a big difference in perception and acceptance of a product. That certainly would apply when dealing with the custom rifle crowd.



Brian, if you send me one of your cases, I'll get the others and make a nice picture comparing all four flavors for future reference. Send me an e-mail or pm.
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Old March 8, 2014, 10:13 AM   #25
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Find mr. taylorce1 on here and buy his rifle, lol. He's already done all the work!
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