For a 257 caliber AR-15, what would you choose and why or, put another way, what are the pro's and con's of the cartridge options listed and similar ones like the 25-45 Sharps without getting into hard to source and work with cases.

I have a 6.8SPC and 300 Black Out so, I'm not really thinking about a 277 Wolverine or 7 Raptor though, Arne makes a really strong case for the 7 Raptor which is pretty easy to source in terms of dies, barrels, etc. However, it is a bit redundant with my 6.8SPC and 300BO.

I am favoring the quarterbore options over something like the 6x223 as I like the bullet options I have a bit better and is a bigger step up from the 223/5.56 premium loads and make the wildcat route more practical and useful. Plus, the extra oomph on a Feral Hog is really helpful.

I'm leaning towards the 223/5.56 case-based options pretty heavily as I don't see enough benefit from a 204R/222 Mag case to be worth the additional effort sourcing cases and similar impacts. I'm also wanting to avoid the 7.62x39, 6.8SPC and, Gendel cases and related magazine and bolt issues.

I have had the 257 TCU recommended to me but, that is one odd poorly documented option. I have been led to believe it is very similar to the 257 Raptor (which is in work) and the 257 Ocelot. I don't get the 25-45 Sharps other than the marketing hype and expect it to go the way of the 376 Steyr and other boutique rounds, comments about neck length, case volume, case shoulder issue and, other similar things also are a factor on this one.

Who has experience with rounds like this? What recommendations or lessons learned do you have? Any strong recommendations for one over the others? I am thinking about an 18" Ranger profile barrel. I'm looking for something effective but not super harsh so, I'm shooting for 2600~2800FPS with common bullets and a 16"~20" barrel.

TIA,
Sid