Another interesting aspect about the Gren is the low SAAMI pressure spec of only 52K psi.
With a long sleek bullet, like the 129gr LRAB, it would mimic the effects of the longer throat of the 5.56/.223Wylde vs the .223. I commonly load the Wylde to 60K psi. With 748, that gets me to 2600fps in a 22" barrel, and 100% fill.
At my altitude, that keeps your velocity at 2k all the way out to 500 yards, and still above 1450fps at 1000 yards.
129gr bullet at 2600 out of a standard AR frame.....hmmmm, that could be interesting.
I hear what you're putting down, but oddly enough at least in my Grendel, the ABLR tops out a little slower than I expected compared to some other bullets. Part of that is probably due to the long nose and deeper seated base to stay within mag constraints (2.300" with ASC mags). I'm able to push a 140gr SGK to about the same velocity as the ABLR (a little under 2250 fps for both), based on case life with loads for both. That's not exact of course, but it's using the same brass, powder, and rifle for both loads. However, at 2,240 fps for my 129 ABLR accuracy load, it's plenty adequate for as far out as I care to shoot. Note that this is similar muzzle velocity to a lot of older "deer gun" cartridges like the 30/30 and 35 Remington, which have killed tons of deer over the years, but that ABLR is a modern bullet design that extends the range and performance envelope significantly.
I will say that when I used this bullet on deer last fall, it was devastating. The exit wounds were larger than my fist, with chunks (not just spray) of lungs and other tissue on the brush around the deer. Since impact velocity would have been somewhere between 1800 and 2000 fps, the 130gr AB probably would have worked just as well but the ABLR gives a wider range of performance in this low velocity round.
