What everyone said, but add this...
In a nutshell, the argument for the 6.5 grendel (and also for the 6.8 SPC) is:
At SHORTER and MID ranges (out to about 300 or 350 yards or so):
1. It exhibits better external ballistic performance than the 5.56x45mm, particularly at those "MID" ranges (but not better than 7.62x51mm, but "good enough"), AND
2. Exhibits better intermediate obstacle penetration than the 5.56x45mm (but not better than 7.62x51mm, but "good enough"), AND
3. (
ARGUABLY) exhibits better terminal ballistic performance than the 5.56x45 (but at least equal terminal ballistic performance, or "good enough"), AND
4. (
ARGUABLY) exhibits EQUAL (or nearly so) terminal ballistic performance as the 7.62x51 (again, "good enough")
, all the while still maintaining the sacred "full auto controllability" of the 5.56x45mm, which the 7.62x51 can NOT do,
AND
At LONG ranges (out to 600 - 800 yards and beyond):
1. The 6.5 grendel is better than ANY other chambering that can be shoe-horned into an AR15 sized platform in BOTH external ballistic performance AND terminal ballistic performance (much better than 5.56x45, slightly better than 6.8 SPC, etc.), AND
2. Is even better than 7.62x51mm from any platform in BOTH external ballistic performance (!!!), AND even at SOME point of long-distance, terminal ballistic performance as well.
Sounds good right?
But the "problems" with that simple analysis that makes the 6.5 grendel seem like a no brainer are:
1. We are NOT limited to the AR15 sized platform. We have the larger ones. Particularly we as citizens/civilians are not constrained by the enormous cost of switching platforms/lowers/armory parts, etc.
2. Just because it's better than 7.62x51 at long ranges does NOT mean that it's better than OTHER chamberings that fit into larger platforms, such as .260 rem, which is superior to any/all of the above at long ranges, and next, for probably the most important factor of them all....
3. Long-Range, Long-Schmange!!! Who cares? A fighting rifle is a SHORT range rifle, period! The 5.56x45 does it all (except thick barrier penetration) at short and mid ranges, and there's never any need to take 400 yard plus shot - if there were, you'd be carrying a different rifle altogether - preferably a turnbolt in a
larger caliber than either 5.56x45 or 6.5 grendel (OR, if in the military, we would holler for the DM in the squad to take the long shot!). The only time this long range rifle is needed, for the 'standard' soldier/marine, is for military volley fire at long range -- but we as citizens/civilians don't ever need / use volley fire!
4. Finally, ye olde false dichotomy (or false trichotomy, etc.) problem, combined with OTHER concerns besides terminal performance, external ballistic performance, full auto controllability, platform size/weight, and ammo size/weight: The 6.5 grendel is not the only round in this same general class or categories of "tweener" rounds - there's the 6.8 spc, which exhibits supposedly better feed reliability (
extremely important issue), and any number of other already-invented or to-be invented wildcats in the 6.0mm to 6.8mm range, which would perhaps combine the best of (or even better than the best of), the ballistic performance of the 6.5 grendel and the feed reliability of the 6.8 SPC.
Bottom line, the 6.5 grendel, and the very similar 6.8 SPC
are indeed just about THE "shiznit" (in a 'standardized', non-wildcat round at least) for civilians in lightweight AR15 style platforms, *if (but only if) you must for some reason have a
just-one-do-it-all rifle*, including looooooong range performance. But a do-it-all gun should not be, and is not, limited to this small light platform. It should be bigger and shooter a better round than
either, preferably .260 Rem or similar. A lightweight gun is is fighting gun is a short-range gun, by definition, period. No need ever for long range shots for civilians (and only in the extreme rarest of circumstances is said full-auto controllability needed for civilians - since 1986). So the 6.5 grendel and similar are arguably a great idea for the militaries of the world (someday; when the inertia/cost factor is mitigated or overcome), but they are a real enigma wrapped in confusion for civilians, IMO. And so, as it stands the 5.56x45mm is THE perfect short-range (to mid-range) fighting chambering - can't be improved upon, except for ammo variations which have already to some extent, and are still being, perfected (that's the prevailing argument at this time, anyway).
And let's not forget that the 5.56x45 is *slightly* more controllable in full-auto than the 6.5 or 6.8 rounds, and the 5.56x45 allows the soldier to carry *slightly* more ammo than the 6.5/6.8 rounds, having lighter bullets. Again, both military concerns, but both weigh in favor of 5.56x45,
not 6.5/6.8.
Those are the basic argument outlines anyway....
And let's also not forget that the true best all-purpose round that hits the sweet spot for the AR15 sized rifles, is probably
not found from any chambering using
any of those 3 calibers: .224, .264, or .277 - rather, more likely, the sweet spot is .243/6mm, or possibly .257 caliber. I'm defining MY "sweet spot" here as a focus on *vast improvements in bullet BC, with only a slight loss of velocity" -- for whatever reason, conjured up by the "Bullet-Inherent-BC-Quirks" gnomes or gods -- probably something like a 6x45 meets that sweet spot the best.
Let's also not forget that punching through intermediate obstable, be they thin & hard like kevlar/steel layers, or thick & softer like sand, brush, small trees, is also mostly a military need, not a civilian need.. but, OK, potentially you could need that in a self-defense scenario.
So there are multiple reasons why the civilian analysis is very different from the military analysis (and your friend is undoubtedly talking about civilian use, becuase guess what - if he enlists, they won't let him use that 6.5 grendel weapon):
1. Inertia with the M16/M4 system - Cost of switching over (not an issue with us civvies) to a different platform
2. Weight of carrying a lot of ammo with mags (not an issue with us civvies)
3. Full-auto controllability (not an issue with the vast majority of us civvies, since who can afford a full-auto lower anymore?)
4. Intermediate obstactle penetration (COULD potentially be an issue with civilians, I suppose, but ordinarily would not be - for example, a soldier might need to shoot an enemy through a house/building wall, without clearly seeing his target. You and I as civvies won't need that, because if we can't see the target, then the target likely is not presenting a threat, in which case using deadly force would not be justified). So this is mostly a military concern, but granted it's somewhat of a civvy concern.
So the point is, what analysis works for the militaries is not necessarily the same analysis of what works for you and me and your friend. The only really important common concern is the weight of the weapon itself. Lighter is better, and in a very LIGHT rifle, a 6.5 or 6.8 round does put a little more punch on a hunting target like a deer than 5.56x45, if you want to hunt with an EBR.
I personally would like to see the
6x45 become standardized and more popular then either the 6.5g or 6.8s. I like the 6mm bullets for good reason, and a round like that maintains 90+% of the recoil-recovering abilities of the 5.56x45, maintains 90+% of bullet yawing induced wound channel capabilities of 5.56x45, with the right bullets, but puts better BC in the air and puts more weight and penetration on the target. That's for a short-range fighting rifle.
In any event, for a "JUST ONE" rifle, including loooong range capability, why not just get an AR10 style in .260 rem like I did and be done with it?