Goldilocks 6mm between 6CM and 6UM?

[eric1115]

What's the best way to hit 3kish fps with a 108 from an 18" barrel? Don't need or want the 3300+ and associated headaches of the UM, and would be happy with CM velocity from a 24" barrel. But since getting my first, I've decided that I want to use suppressors on everything. Bonus points for standard bolt face and taking advantage of Tikka mag length, as it would be sweet to be able to rechamber Tikka .243 8 twist and go.

Extra bonus points for something with good quality brass and chamber dimensions for good brass life. It would be nice to be able to fire form 200ish pieces for barrel break-in and speed-up and be set for the life of the barrel. Head stamped brass would be best of all obviously.

6x55 Swede? .243AI (seems like it's still not quite there, but probably easiest option)? 6x284 may be a little much but maybe not if loaded mild? Fast twist 6mm rem?

I know 6CM will realistically do what I need, but I like to daydream.

 

[hereinaz]

It’s really 6 creed, 6xc, .243 ai, etc for the case size and dimensions. Otherwise you get to the point it climbs the curve of being overbore.

 

[atmat]

How far are you trying to shoot? Even a 16” suppressed 6creed will get you to further distances than most should shoot animals while maintaining 1800 fps for expansion.

 

[eric1115]

No argument there, I know a 6cm will do it ok. I've never shot an animal past 600. I practice out to 1k, and I can shoot out to 1400+ at my range.

I suppose part of it is that I shoot my 7mm RM (2850, .680 G1 and my .308 (2800, .530 G1) at those ranges and see a noticeable difference in hit rates. Going to a short 6CM at 2700 or less, .546 G1 seems like a step in the wrong direction, and I suppose I was hoping to get some of the benefit (danger space, slight wind advantage) of the UM with only some of the downside.

 

[ARK_Ginger]

Just rambling here, but I had a similar thought and concluded either a 6 PRC or 6x284 would both be a good fit.

 

[amassi]

6prc
Way more brass availability than the 284
Simple set of bushing dies
Easily hit your velocity goal
No Fireforming, load and shoot


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[Dioni A]

22 creedmoor is what your looking for. The BC on the 88 ELDM is better than the 108 and it can push it 200-300 fps faster with less recoil.

 

[ARK_Ginger]

6prc
Way more brass availability than the 284
Simple set of bushing dies
Easily hit your velocity goal
No Fireforming, load and shoot


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PVA also offers the 6 PRC in a prefit.

 

[eric1115]

22 creedmoor is what your looking for. The BC on the 88 ELDM is better than the 108 and it can push it 200 to 300 ft per second for it faster with less recoil.

I have definitely considered that too. It seems like 22cm, 6.5-284/6.5PRC, 7PRC all push similarly proportioned heavy for caliber bullets at good but reasonable speeds, and we seem to be missing that cartridge for the 6mm (I think due to bullet options as much as anything, a 120 eldm is what we really need to get that .285-.295 sd, .330+ G7 6mm)

 

[Dioni A]

I have definitely considered that too. It seems like 22cm, 6.5-284/6.5PRC, 7PRC all push similarly proportioned heavy for caliber bullets at good but reasonable speeds, and we seem to be missing that cartridge for the 6mm (I think due to bullet options as much as anything, a 120 eldm is what we really need to get that .285-.295 sd, .330+ G7 6mm)

Does seem like the world is missing a Magnum 6mm that's commercially available and not insanely overbore

 

[6mm Remington]

6mm Remington

 

[Dioni A]

6mm Remington

Doesn't come with the right twist to work with long heavy bullets and I'm assuming Remington is your only option for brass. Its not really a performance gain over the creedmoor either. Once you try and run it on a short barrel with a 108 your getting into pretty anemic performance.

 

[Ice-kub]

I was just googling 6prc, thinking of a rebarrel of the 7wsm

 

[Bfish22]

Just rambling here, but I had a similar thought and concluded either a 6 PRC or 6x284 would both be a good fit.

That’s funny. I just bought a 8 twist tikka 243, and before it even got to my ffl, was already thinking of rechambering it to either the 6prc or 6x284….

 

[amassi]

That’s funny. I just bought a 8 twist tikka 243, and before it even got to my ffl, was already thinking of rechambering it to either the 6prc or 6x284….

6x284 just swap bolt stops to the long action and get some king action mags and your off tot he races


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[Bfish22]

6x284 just swap bolt stops to the long action and get some king action mags and your off tot he races


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Yep!

 

[eric1115]

6x284 just swap bolt stops to the long action and get some king action mags and your off tot he races


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That's certainly a big part of what appeals to me about that chambering. Seems fairly painless, though I've never dealt with a wildcat that needs fire forming, neck turning, etc.

 

[hereinaz]

IMO, if you want magnum, run a 25 PRC or 25 SST and get the added benefit of extra bullet weight.

I agree with the 22 creed running heavies, I know guys that are loving the 22 GT.

But, if you want a fast 6mm, the prc or 284 seem easy. The 6 SST is a possibility. You can get an idea about velocity on the Sherman Facebook page snd some discussions.

 

[amassi]

That's certainly a big part of what appeals to me about that chambering. Seems fairly painless, though I've never dealt with a wildcat that needs fire forming, neck turning, etc.

Just talk to your smith about reamer dimensions
There a ton of 6-284 reamers a “no turn” reamer should t be hard to find


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[PathFinder]

Fire forming the 6UM is very easy, but the 6 PRC is a fine option if you want to avoid that.
Either cartridge can be put on cruise control with H1000 and lighter bullets. Not sure what the difference would be over the life of the barrel but probably 100 rounds at least vs high pressure N570 loads.