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View Full Version : Has there been a necked-up 5.56/6.5 round made?


ABNAK
10-08-17, 20:13
Kind of like a 5.56 case was necked up to .30 caliber for 300BLK. Has one been done with a 6.5 bullet?

I would think that using a 300BLK-like round in 6.5 would be cool. 6.5 flies very well and you should get a tad faster velocity from it. Obviously would have to fit into an AR magazine.
steyrman13
10-08-17, 20:38
Kind of like a 5.56 case was necked up to .30 caliber for 300BLK. Has one been done with a 6.5 bullet?

I would think that using a 300BLK-like round in 6.5 would be cool. 6.5 flies very well and you should get a tad faster velocity from it. Obviously would have to fit into an AR magazine.

I would think that would be the issue. I mean they have the 6.5 Grendel but 6.5 bullets are pretty long for such a skinny case. I'm not sure you have the volume available for the length of bullet to diameter of case ratio. I could be wrong
ABNAK
10-08-17, 20:55
I would think that would be the issue. I mean they have the 6.5 Grendel but 6.5 bullets are pretty long for such a skinny case. I'm not sure you have the volume available for the length of bullet to diameter of case ratio. I could be wrong

Hadn't thought about that. Good point.

Grendel won't fit in a regular AR mag though like 300BLK will.
MisterHelix
10-08-17, 21:21
Yeah, 6.5PCC...but it's not a very popular wildcat.

The 6x45 and 277 wolverine are also worth considering if you're wanting to stick to the .223 parent case.
sucker76
10-08-17, 21:28
There have been several. Here is what I found.
25-45 Sharps
6mm/TCU
6.5mm/TCU
7mm/TCU
30/TCU
6.5PCC
It looks looks the TCU family was intended to be used in the Thompsons with barrels <16". The 25-45 Sharps had some OK advertising a few months ago but I haven't seen from it since. I think it's claim to fame was a deer hunting caliber in an AR. Some states have a .243 (6mm) minimum. I haven't read too much about the 6.5PCC.
markm
10-10-17, 11:00
What would be the upside to this? It strikes me that any gain in bullet BC would be more than offset by velocity loss.
ABNAK
10-10-17, 18:35
What would be the upside to this? It strikes me that any gain in bullet BC would be more than offset by velocity loss.

Honestly I was curious. Looked at the 277 Wolverine for shits and giggles......110gr bullet at ~ 2500+ fps. Not too shabby (granted that was a 16" barrel, obviously an SBR would be lower). This is essentially a 6.8SPC in a .223 case. They are not as aerodynamic as the true 6.5 clan can be but it was interesting nonetheless. Doubt I'll be converting anytime soon but the premise was interesting.

I hear talk that the U.S. military's next cartridge will be of the 6.5 variety. If they can load one with enough "umph" in a .223 case that negates bolt and magazine changes = cost saver? I dunno......
MarshallDodge
10-17-17, 09:34
A friend, who is a big Thompson Contender fan, has one chambered in 6x45. He does pretty well on the prairie dog fields with a 70 grain Speer bullet. I have seen him make headshots on a steel silhouette at 500 yards with it.

223 is just so versatile and cheap to shoot as it is, and the 6x45 only offers minimal gains in performance although it does well in short barrels. One solid reason for the 6x45 is that in some states there is a minimum caliber requirement for big game and the larger diameter bullet can get you there. On an AR, all you would need is a barrel swap.
yellowfin
10-22-17, 21:31
Better than the .277 Wolverine would be that 6x35 that Knights cooked up but for some reason never SAAMI'd.
Bimmer
10-22-17, 23:42
Call me stupid, but I think a .32 or .355/9mm straight-wall (or only very slightly tapered) cartridge based on the .223 would be neat... Kind of a modern day .30 Carbine.

Obviously it wouldn't be good long-range, but it might be a good SBR cartridge.
Arik
10-23-17, 09:32
Call me stupid, but I think a .32 or .355/9mm straight-wall (or only very slightly tapered) cartridge based on the .223 would be neat... Kind of a modern day .30 Carbine.

Obviously it wouldn't be good long-range, but it might be a good SBR cartridge.Reminds me of the Soviet 9x39. 7.62x39 case necked up to .356 9mm 260gr.

Slow, subsonic for short range sniper rifles or SBRs

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Eurodriver
10-23-17, 09:40
I hear talk that the U.S. military's next cartridge will be of the 6.5 variety. If they can load one with enough "umph" in a .223 case that negates bolt and magazine changes = cost saver? I dunno......

Where do you hear these things??
ABNAK
10-23-17, 17:07
Where do you hear these things??

Many different places to include here on M4C. Not that it's going to happen anytime soon, but that if/when a new cartridge is adopted it would likely be of the 6.5 variety (not in a necked-up 5.56 case, that was a question I was asking).
vicious_cb
10-23-17, 17:31
Many different places to include here on M4C. Not that it's going to happen anytime soon, but that if/when a new cartridge is adopted it would likely be of the 6.5 variety (not in a necked-up 5.56 case, that was a question I was asking).

That died with the interim combat rifle. There is zero reason to incur a weight penalty with a heavier round than 5.56 when you can't even produce soldiers and marines who are capable of utilizing that extra capability.
ghostly
10-23-17, 18:19
.25 caliber is the right balance.


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