6SLR vs 6CM

[Nomad47]

WHEN my 6-284 barrel wears out I want to switch to one of the above mentioned cartridges. But, which one. From what I have read on here, the SLR does not need fire forming and works well with cheap Winchester brass. On the other hand, the CM guys say barrel life is great.

How do the two compare for case capacity, velocity, accuracy, ease of finding an accurate load, die availability? Do any of the barrel manufacturers offer either cartridge as a Savage Pre-fit?

I plan on a 28" 8 or 8.5 twist. And will shoot hBN coated 105 AMax for varmints and hBN coated 105 Hybrids for target & informal competition.

 

[NateG]

You summed up the pros and cons pretty well. The extra capacity of the 6CM buys you all the usual things you can get with extra capacity--or, you can run the much slower powders (e.g., H1000) and get the same (or a bit better) performance and much, much longer barrel life. The primary advantage of the SLR is no fire forming. For what it's worth, I've got a 6CM and really like it. (For across-the-course highpower. I'll probably shoot it at long range, too, but recently I've been using my palma rifle exclusively)

One caveat: with the 6CM, get a .237" bore. I'm not sure if the 6SLR is picky about the bore dimensions (.236" or .237"), but the 6CM seems to be. However, my experience is that the 6CM (with the .237" bore) is not picky at all about loads. I've shot a 100-9X or better at 600 with three or four different loads with three different bullets (Berger 108s, 115s, and 105 hybrids), including a fire forming load with thrown charges.

Also, there's not much harm in going to the faster twist (7.5") for the 105s, and it does give you some options in case you end up wanting to shoot the 115 class bullets. I had planned on shooting 105 Hybrids, but as it turned out, my gun liked the 115s, so that's what I run instead. (Not to say the 105 Hybrids didn't shoot well... but the 115s were what the gun preferred) And if you're planning on the 105 Hybrids, you might want to go 8" rather than 8.5", since the hybrids are a bit longer than the rest of the 105 class.

 

[offgrid]

I've shot both.

Started with a 6SLR, gave up on the barrel at 970rds.

Have 2300rds on the 6CM, shooting very well. Guessing the barrel will go another 1000rds? I shoot steel matches with fellow Colorado member Hoser, I believe he pulled his last 6CM barrel at 3400rds. In hindsight wish I would have paid more attention to what Hoser was doing and chambered a 6CM from the get go.

 

[22BRGUY]

Hi guys
I'm looking at these also...My understanding is that the SLR case has very slightly more case capacity than the CM....On Whitleys site about the 6.5's, it seems the SLR has about 2 gr. more water capacity. Am i seeing this right or did I misread it? Its hard to understand how a +- 2 gr capacity difference could make that much difference in barrel life....
Thanks guys

 

[NateG]

The 6CM has more capacity. The 6SLR gets to the sharper shoulder angle (30°) by making the neck longer (and keeping the shoulder-body junction in place, so no fire forming, but possibly requiring neck turning). The 6CM gets to it's sharper shoulder angle (31°) by keeping the neck-shoulder junction in place, and moving the shoulder-body junction forward (so fire forming is required, but neck-turning is less likely to be necessary). So the 6CM gets a bit more capacity--and that little bit of capacity is (generally) used to get the slow powders up to a reasonable pressure, and using the slow, lower energy, powders is what buys you the extra barrel life.

Both have advantages over the other... but for me, fire forming isn't a big deal, since I have 200 yard standing stages where I can fire form for "free". For a prone-only shooter, having to fire form may be more of a concern and may be worth the other side of some of the tradeoffs.

 

[22BRGUY]

Thanks Nate...I just double checked on 6mmar.com on the 6.5 SLR vs 6.5 CM and looked at the pics and thats where it says the SLR has more capacity. Maybe it comes out different for the 6.5's vs the 6's. Your info is helpful tho and thanks

 

[rcw3]

Started with a 6SLR, gave up on the barrel at 970rds.

Probably a bum barrel - that's way too early.
Robert

 

[NateG]

Thanks Nate...I just double checked on 6mmar.com on the 6.5 SLR vs 6.5 CM and looked at the pics and thats where it says the SLR has more capacity. Maybe it comes out different for the 6.5's vs the 6's. Your info is helpful tho and thanks

That's the 6.5 Creedmoor. The 6CM is the 6mmCompetitionMatch, which, like the 6SLR, is based on the .243 Win. The namespace collision between the 6CM and the 6.5Creedmoor (which sometimes gets abbreviated as 6.5CM) can be a bit confusing, to say nothing of what happens if you neck a 6.5Creedmoor down to 6mm...

 

[22BRGUY]

My dumb Nate...thanks for clarification.....Is there anywhere that you might know of that I can see a pic or diagram of the 6CM?
Thanks much again
Dennis

 

[NateG]

My dumb Nate...thanks for clarification.....Is there anywhere that you might know of that I can see a pic or diagram of the 6CM?
Thanks much again
Dennis

I posted my version of it here: http://forum.accurateshooter.com/index.php?topic=3783720.msg36128855#msg36128855

The canonical version of the 6CM has a shorter freebore (by .060" or so), and is slightly tighter in the case head diameter. Mine was cut longer to take advantage of the bigger AICS mag box (I use a R700 in an Eliseo RTS, rather than a Tubb gun which has a shorter magazine) and the body is a bit bigger to allow Lapua brass to extract easily. I think there's a print of the original version attached somewhere in the 17 pages of that thread.

However, I haven't had a chamber cut with the new reamer yet, though I've got it sitting in my basement waiting for a) my current 6CM tube to wear out, and b) the huge lead time on my order for a new tube. I'm currently using the standard version which plays very nicely with Winchester brass and the AICS mags, despite the extra room. (Even for the short 60 grain bullets on the 200 yard line)

 

[22BRGUY]

You're awesome Nate and thanks much again. Now you've got my wheels turning about necking that up to a 6.5 in a bolt gun.......hear the squeeks?
Best to you
dennis

 

[NateG]

I think Joe (the 6CM creator) tried it, and didn't end up pursuing it very far. I think the issue was that in order to get the benefit of the slow powder, you needed a much larger capacity--and a 260-improved-sized case (which is what you would have) doesn't have enough capacity. Which makes sense, since the 6.5-284 has a bigger body diameter than the 260, and is a bit longer as well. You don't see many (any?) folks running H1000 in the 6.5-284 to try to get better barrel life. Probably because the capacity isn't there to get the pressure up into the ballpark--and the result is low speeds and probably inconsistent speeds as well.

That's not to say that you couldn't build a 260 improved, but it wouldn't have the things that make the 6CM so gentle on barrels. (The ability to use a bunch of very slow/low energy powders and still get the pressure into the right envelope to get good and consistent performance)

 

[Nomad47]

Thanks, guys. A lot of good info so far.

So it appears that H1000 is the powder of choice for the 6CM. Do either of the cartridges do well with H4831sc and 105 class bullets? Does the 6CM do best with one particular brand of brass? How about die availability? And, to repeat, do any of the barrel manufacturers chamber either as a Savage Pre-Fit? I think Preacher has a 6SLR reamer and will do a Savage Pre-Fit.

 

[NateG]

I haven't played with 4831 much, but I would imagine it'd be a good choice... provided you're willing to give up some of the barrel life--which would reduce a lot of the appeal of the cartridge for me. Whitley likes it in the 6SLR, and the two are similar enough that I would expect it to work in the 6CM as well.

I don't know of anyone selling pre-fit Savage barrels in 6CM, but I would imagine there are plenty of gunsmiths who can do it... all they'd need is the appropriate reamer/gauge. Dave Bruno in PA certainly has the reamer to do it. Chad Dixon (IIRC) is another name that often comes up in regards to building 6CMs, but unlike Bruno whom I can recommend, I've never had him do any work for me.

 

[Nomad47]

It looks like dies and go gauges could be a little hard to get. I was just at PT&G's site and I searched for 6mm CM and 6CM. Nothing for a go gauge. Or will some other go gauge work?

 

[offgrid]

It looks like dies and go gauges could be a little hard to get. I was just at PT&G's site and I searched for 6mm CM and 6CM. Nothing for a go gauge. Or will some other go gauge work?

I believe Dave Bruno is stocking Redding FL bushing sizers. You could also check to see if Redding has a FL sizer in stock, and have your favorite Redding dealer order it for you, they will not sell direct. I'm using a Redding 243 Comp seater, works well.

Ya', H1000 is the powder to use.

Chad Dixon chambered my 6CM. Having another one chambered next by a local gunsmith who recently purchased a reamer from PT&G.

 

[Dgd6mm]

Bill,
I bought my Go Gauge from PT&G. I have 2 barrels that go on Savage actions and 1 on a Hall. Dave Bruno chambered my 6CM's and he headspaced the first one. I FF brass and made a go gauge out of a ff piece. I've had no problem with this but once in a while I swap the barrels from 1 action to another and just decided a go-gauge would be nice to have.

 

[Nomad47]

Whew!! I just finished reading ALL 17 pages of the 6CM topic.

I am interested in the 6CM but I won't rule out the 6SLR or the 243 Imp 30. But whatever it is that I end up with I have two requirements.
1. A Go gauge. (I think I read somewhere that the 243 Imp 30 uses a .308 Go gauge.) Don't know squat about the other two.
2. The barrel chambered so I can screw it on one or both of my Savages (one is a small shank and the other a large shank) using my tools and barrel nut.
I wish Criterion offered either in a Pre-Fit. I guess y'all can see I don't want to spend a bunch of money on this project.

 

[rcw3]

FYI - 243 Imp 30Ëšdoes use standard 308 "go" gage - I designed it that way so it would be real easy for just about any smith to chamber a barrel for it (every smith I have ever known has a 308 Win "go" and "no go" gage). We also carry dies in stock for it. You can use 6CM loads in it with the same results, H1000 powder, etc. and it's case capacity is minutely larger than a 6CM.

Robert

 

[Nomad47]

Well, Robert, that is good news. Now if you could convince one of the barrel makers to offer it in a Savage Pre-Fit. . . . . I just don't feel like spending $300 plus to buy a barrel, then another $200 plus to have it chambered.
I have 3 Criterions and 1 Shilen (all Savage Pre-Fits) that shoot well (that means good enough for me) and all were less than $350 chambered.