There are some issues to be aware of with 6.5G. The taper is too high for the AR platform (which was designed for the relatively straight 5.56) so everything in the feed geometry is subtly the wrong shape, just like with a 7.62x39 AR
Grendel has a lot less taper than 7.62x39 --a lot of people wrongly assume it is 6.5x39. The feeding issues --which are real-- stem the hard limitations of the AR platform; Grendel is just barely too wide for proper feeding from double-stack mags which is why there is so much sideways pressure on the shorter feed-lips (the part of the round held by the lips is further to the side than for narrower cartridges, and therefore more sideways force is needed to resist the mag spring's force) but too narrow to simply feed single-stack like the Beowulf. It also stacks at a different angle than 5.56 so the follower needed some redesign to do higher capacities.
All that said, it does generally work, though only with steel body mags. And unfortunately, the mags on the market aren't always the best quality (my 24rnd mags have a lot of burs and are ridiculously hard to strip rounds from; my 10rnd is more normal). If the AR magwell were even .05" wider, the feed lips could be properly reinforced, and aluminum or polymer mags with much less friction would be doable. But again, the Grendel has always been about pushing right up against the limitations of the AR platform, so we'll just have to wait for polymers to get a little better before we get mags as good as for 5.56. 5.56 AR15's had crummy mags for decades, so I'm not expecting the moon right away (but soon would be nice)
Similarly, the case head is larger and more importantly deeper than the 5.56. This weakens the bolt, which is already the weak point on the AR15. Depending on how the bolt is designed and chamber cut (there are two versions of the 6.5G chamber/bolt) you get some mix of risk to break bolts and break extractors. There's also the issue that bolt thrust (pressure times case cross section) is higher in the 6.5 G than it is in 5.56, which makes the part breakage risk yet higher if loaded to max. I would go so far as to say that the SAAMI max pressure is simply wrong - the guns can't take it.
You are more right than wrong, but there's a ton of confusion in this area because of industry tool-bags making up stuff as they went along to stack up money while they could.
The Grendel bolt is deeper than the 7.62x39 bolt. There is a parody of the chambering that is reamed deeper so the same ammo can be shot using cheaper x39 bolts; this was created during the big Panic when Grendel bolts were in short supply. The reason the Grendel bolt is deeper in the first place is because the cartridge's rim is that much thicker than 5.56's. The cheap x39 bolts simply have less material in the extractor claw and are therefore weaker, but x39 is so tapered that it generally requires less extraction force, so there's no issue. Grendel is nearly straight-walled like 5.56, and has much more surface area to boot, so the decision was made to set the bolt face back so the standard-thickness extractor claw geometry could be used.
The bolt breakage issue has been resolved. Early on, the Grendel chamber had a leade optimized for accuracy; that is, the bullet was nearly up against the rifling when chambered. People liked that it shot well, but because the bullet did not get a running start before hitting the rifling, pressures reached higher peaks for a given powder/bullet load. Around the same time, a vendor sold a number of improperly heat-treated bolts (or was it just they used a cut-rate alloy?) which made them even more sensitive to the force from that peak pressure. On top of all this, the Grendel was designed to use a slightly higher peak bolt thrust than 5.56 from the get-go, again in keeping with the theme of pushing against the limits of the AR15 platform. Lastly, there were a lot of bright-eyed reloaders enamored with their accurate cartridge and long-range-capable VLD projectiles; like all benchrest cartridges, they pushed the power limits to try and flatten out the trajectory further. All these things led to a number of broken bolts, namely the bad batch by that manufacturer. Today, Grendel bolts are typically 9130 steel (slightly better than mil-spec), are properly heat treated and inspected (MPI), the chamber leade has been modified to give the bullet an easier ride into the rifling so pressures don't go quite so high, and shooters have come to realize that pushing beyond the ~40,000psi range just makes the gun less accurate. There is also a better understanding of the impact gas systems have on stressing bolt components (i.e. don't put a carbine-length on a rifle) which also helps.
To further confuse the market, a "CVS-equivalent" version of the chamber (the proper-depth Grendel on) was created by Les Baer because they wanted the freedom to modify the chamber dimensions to suit their production needs without going through Bill Alexander who had the patent rights on the design. LB wanted a simpler single-taper leade as opposed to the two-taper Grendel leade, since this cut more chambers before dulling out of spec. So they created this 264LBC cartridge, which for all intents & purposes is the same thing (i.e. it shoots the same 6.5 Grendel ammo as all the other chambers).
A lot of complaints are heaped on Bill Alexander for how he managed the deployment of the Grendel, but frankly all his worries about the market distorting his product for short-term gain and confusing customers in the long run, have proven to be completely justified. Which is why I don't begrudge him for playing his cards close to the vest as far as issuing licensing rights to produce "Grendel"-named barrels, reamers, and ammunition early on, as opposing to putting it out there for SAAMI to 'enforce' more weakly (case in point; PPU made a large batch of Grendel that was SAAMI approved...turns out the case head base dimensions were larger than they should have been, and the powder load a much higher load than spec'ed. It was eventually recalled, but not before I had a bunch of rounds get stuck in my rifle from vendors who continued selling the bad ammo anyway)
TCB
. The Grendel is well designed and perfect for the AR15 platform, and the Creedmoor is an excellent choice for the AR10.
