I don't owe you an appology, I expressed skepticism of a rather far-fetched claim, which was reasonable at the time. I'm still a bit skeptical of the 14k distance you've stated, when you get down to it.
I never said you couldn't take down a base without an LOS. I said you can't do it quickly, reliably, and efficiently. And unless you're firing from a pre-ranged possition, with pre-marked firing points, or are firing from a possition of exact known range to a target, and are really quick with a field map and some math, you can't do it quickly.
This makes it inefficient, becuase you have to do a lot of preparation to quickly and reliably hit a target. That in turn limits its usefullness.
Oh, and the M3 tank gun fires the same round as the M1897 field gun, which had a maximum range of 7,500yds.