I only fired the 9mm tracer version of the AT-4 in my regular military sevice training, but while preparing for my UN mission in Bosnia (BA01 + BA02, 1993-94) I actually got to fire a few "fullbumpa" AT-4's (concrete or something like that instead of the high explose shaped charge, but still a real 84mm projectile).
My platoon only got to fire one real AT-4, and that turned out to be a bit of a disappointment for the guy doing it. FMV (Försvarets MatrielVerk) was there to inspect the live firing (apparently it is quite rare), and they asked him to pre-set his sights before going into position (stupid!). We had just gotten new blue kevlar helmets, and they were hard to fasten properly, so they swung around a bit on your head. Apparently the guy's helmet knocked the rear sight down a few notches when he laid down in position, making his aim go way off. Instead of piercing a rather sturdy looking piece is steel 100m away, the missile hit the ground after only 70m or so, digging a nice little hole.
By the way, during the same fire exercise where I got to try the "fullbumpa" AT-4's, our turret gunner got to fire 1200 rounds in 3 hours using the 20mm AKAN in the PBV (301? can't remember, the old Hägglunds thing). That's aparently quite a lot, even when compared to how many rounds a turret gunner fires during his entire training (and this was during 3-4 hours).
Hmm, what more did I fire that night? A bunch of "mellanlys", 600 rounds of 5.56 with my AK5, a full box of 7.62 with a KSP58, a few 9mm rounds with a Glock (borrowed from a captain) and one round with a PSG90. We were designated as fire-team for the exercise, and were to support other platoons during their practice-runs. We had a silly amount of ammo in our reload station. I think I have a picture of it somewhere actually. While all the other groups had a few boxes of 5.56, 7.62, mellanlys, AT-4's, 20mm AKAN, we actually had crate-after-crate-after-crate full of it. We didn't even manage to finish everything off because you can only reload your AK5 clips so many times before your fingers start to ache.
The shaped charge in the AT-4 and GRG is good for knocking out regular armoured vehicles or concrete bunkers, but against a modern MBT they are no match. A modern MBT has active armour that deflects much of the energy created by the shaped charge. The energy left after going through the active surface is no match for the very thick hull, at least not in the front and in the sides.
To take on an MBT you need something like the Rb56 "Bill" or the famous TOW. Rb56 is a wire-guided-anti-tank-missile (WGATM) that has a range of up to 2200 meters, can be carried and deployed by 2 soldiers and strikes the tank from above where the armour typically is weaker.
Flow, I did 10 months of regular "mandatory" military training as an arctic ranger (at K4 in Arvidsjaur). I sort of liked the military life, so when Sweden decided to send troops to Bosnia for a peace-keeping UN mission I applied and got in. I spent a year down there.
/Daniel