Has there been a necked-up 5.56/6.5 round made?

[ABNAK]

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]

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]

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]

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]

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]

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]

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]

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]

Better than the .277 Wolverine would be that 6x35 that Knights cooked up but for some reason never SAAMI'd.

[Bimmer]

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.