6SLR vs 6CM

[LRPV]

Nomad, I'm pretty sure that Criterion will chamber with your reamer if you are so inclined. Of course it costs more to buy the reamer, but you would get the same Criterion quality you're already used to.

 

[Nomad47]

Thanks, LRPV. That is something that I am considering.

I'm also considering just going with a standard 243 AI. That would be the cheapest route for me to go. Criterion already offers that chambering. And there is a better selection of dies.

 

[Dgd6mm]

It gets tougher everyday deciding on a 6MM. The .243 AI Criterion pre-fit would be a good choice. 105 Hornaday BTHP's and slow burning powder may work well for you, there is always meloniting also.

 

[racesnake]

Wonder if the 6mm Rem or the AI version would respond to the slow burning powder/longer barrel life equation the way the CM does? Any comment?

 

[Nomad47]

Good question, Racesnake.

Thanks, Don. The 30 degree shoulders of the other three may be more accurate. But for what I would be shooting, the AI would probably be good enough - with a better selection of dies. I don't think a .308 go gauge would work for the AI, but I assume PT&G makes a 243 AI go gauge.

 

[NateG]

Wonder if the 6mm Rem or the AI version would respond to the slow burning powder/longer barrel life equation the way the CM does? Any comment?

Probably. There's nothing magical about the 6CM's design--just a way to get enough capacity to use the really slow powders. (It happens to be pretty easy to get shooting, as it turns out, too.) I've also heard a few folks raving about the barrel life in the 7RSAUM using H1000, rather than the more common 4350. (and a few muttering about how H1000 doesn't shoot as well as 4350 in the RSAUM, too) H1000 seems to be enough cooler and slower burning that the extra capacity required to make use of it is more than offset by the gentler-on-the-barrel powder and the life's pretty good.

The downside is that you're using more powder for a given bullet speed, and that means marginally more recoil and muzzle blast. But nothing's free when you're choosing your cartridge...

 

[Nomad47]

NateG, that last statement of yours couldn't be more true. To gain one thing, you must give up something else.

Actually, barrel life isn't all that important to me. Shooting 2000 rounds per year with the ability to replace a barrel for a little over $300 is why.

 

[LRPV]

I like the idea of Whitley's 243 improved 30*. He seems to do all the leg work getting everything worked out to where it's kind of a turn key wildcat. He gets the dies, has them for sale for a decent price for the most part. Midway shows 243AI Redding S FL with micro seater for $173 out of stock. Robert shows the same dies for the 30* improved for $220.

With all of the more than stellar comments on the 6CM regarding accuracy and barrel life it would be very hard not to pick it, but it looks like the 243 imp. 30 would be close enough to it to get the same results but maybe easier to get dies. There was some discussion of guys having problems using Lapua brass in some of the 6CM chambers so that would be something to nail down before the chamber was cut if it was me.

 

[Dgd6mm]

6CM dies are not that hard to get.
Ask for the .243 Egolf IMP.
3700 rounds down my 1st barrel that is not melonited and still shoots itty bitty. Not here to pimp one round over the other, just know the 6CM well. I would shoot any of them that was capable of using H-1000 to it's full potential. I like both of Robert's cartridges, between the 6SLR or the .243 Improved 30*, well that would be a tough choice.

 

[Nomad47]

Maybe I should re-title my topic "6CM vs 6SLR vs 243 Imp 30 vs 243 AI".

I think the four all have similar case capacity. Three have 30 degree shoulders, one 40 degrees. All made from the 243 case.

 

[Hoser]

I have been shooting the 6CM for several years.

For me, it works perfect. I use H1000, 115 DTACs, Lapua and Win brass.

I am using a mag fed rifle and the 30' shoulder still allows easy feeding.

One of these days I will have a AR-10 barrel chambered for it to stick in my OBR.

 

[NateG]

For what it's worth (which isn't much) the 6CM is a 31° shoulder. Not that it makes any practical difference... unless you happen to be grinding a reamer, of course.

 

[rcw3]

I have been shooting the 6CM for several years.

For me, it works perfect. I use H1000, 115 DTACs, Lapua and Win brass.

I am using a mag fed rifle and the 30' shoulder still allows easy feeding.

One of these days I will have a AR-10 barrel chambered for it to stick in my OBR.

I would not recommend a 6CM or .243 Imp 30Ëš using H1000 in an AR-10 - - that powder has such a slow burn rate that your port pressure will be so high (even with an extended gas port) your gun will hammer itself very hard when cycling unless you have a puny little gas port - - and if you have a little gas port like that, then the rifle will be marginal for cycling properly with other powders like H4831SC or H4350 - - been there, done that. I have an AR-10 upper that I set up for use with H1000 and it won't even cycle properly with H4350 and with H4831SC it is marginal, yet it cycles pretty hard with H1000. For an AR-10, set it up to work with faster powders than H1000 and stay there - - besides, H1000 generates a huge muzzle blast and a lot more recoil because of the sheer extra volume of gas being expelled from the muzzle of the rifle - - just the wrong set up for the application IMO.

Robert

 

[CanusLatransSnpr]

Nomad, the 308/243/260 go gauge is actually used as a no go gauge in the ackley improved chamberings based on this parent cartridge. Just snug the barrel up till you can only turn the bolt about 1/4 turn on the 308 go gauge, perhaps a little less, and check for a crush fit on a piece of virgin brass. It wouldn't hurt to strip the bolt of the ejector and firing pin for this process either. There should be a slight ring on the go gauge where it meet the neck/shoulder junction in the chamber also! Hope this helped??

Mike

 

[Dgd6mm]

No need to re-title Bill. Back to your original questions. Both the 6SLR and the 6CM use Winchester brass without issues. Robert's 6SLR is simple to form brass from what I've viewed in the video, just lube and run thru the die. The 6CM will run a 115 gr. bullet fast and of course a 105 even faster using H-1000, not sure how fast, but accurate also at 1000 yards. Both of these cartidges WILL do the JOB. No PRE-FITS available. Like I said TUFF choices.

 

[Nomad47]

Don, my 6-284 has 300 rounds of mine thru it plus another 50 according to the seller, so I have some time to decide. I like the 30/31 degree shoulders but I guess I would have to buy a reamer if I want one of the manufactures to do a pre-fit. My other choice would be to find a 'smith with the reamer & willing to do the pre-fit.

Mike, "Hope this helped." Yes, indeed, it helps a bunch. Thanks. I'm thinking the barrel can be screwed down to hit the go gauge. Then the bolt could be opened and the barrel torqued. There is a little creep as the barrel gets torqued and that should make it just right. It should be easy enough to check.

 

[CanusLatransSnpr]

I think you're on the right track there sir! It would be easy to check. As I said, just plop in a virgin piece of brass and close the bolt slowly and you should feel some resistance indicating a crush fit as the chamber contacts the neck/shoulder junction of the brass! Headspaced this way eliminates the need to load bullets long to keep the cartridge up against the bolt face also. It still couldn't hurt to load a bullet a few thou into the rifling anyways!

Mike

 

[Nomad47]

That is an excellent point about the fire forming, Mike. And so what if the headspace would happen to be a couple thou off from spec - case capacity wouldn't be affected that much and the f/l die could easily be adjusted.

 

[CanusLatransSnpr]

If you were a couple thou "long" on the headspacing then yes a full length die could clean that up but, if you were a couple thou tight? The die would bottom out on the shell holder before the shoulders were bumped back. I have a .243 McGowan barrel that was headspaced tight and it is a sob to bump the shoulders back on! That being said, I'm going to do what you're proposing. I'm going with a criterion .243 A.I. and I have the 308 Win go gauge coming from Sinclair/Brownells. When I get that go gauge and the tools to swap barrels, believe me I'm going to adjust the headspace on the std. .243 Win! In that situation I would just put a piece of scotch tape on the back of the go gauge and then it became a no go gauge where I would adjust to where the bolt only closed 1/4 turn! Hope I made sense?

Mike

 

[CanusLatransSnpr]

As I think about it more, the bolt closing on virgin brass will tell the story! If you can't close the bolt on virgin brass? It's too tight and conversely if the bolt slops down in the locked position with no resistance? Then its too loose! You have to swap back and forth from the headspace gauge and brass till you get the sweet spot.

Mike