Unless it's a ?-5-7 pillbox NCA where you need a 15 to gain entry (57L or better). You would need a 76mm Sherman. However even a Stuart 37LL is good to go against a ?-3-5.
lighter pillboxes are the stuff that light armor was made for - terrorize enemy infantry in their "impregnable" fortifications.
The best part is aq still applies, as does point blank fire (or the -1 for 2 hex range), and the hits are 2 flats, over and over. a decent light AFV vs a x-3-5 pillbox with a 2 lbr (40L) or better - will finish off those things inside out with AP ammunition from a NCA LOS in no fear at all of enemy retaliation from inside the bunker, and the ROF means liklihood of multiple hits and multiple 2 FP flat attacks on the occupants will do faster damage than trying to approach and get in for either a CC or a DC or FT attack. - and if enemy inf rushes you, well those Stuarts sure got a lot of MG's, as do Mk III panzers, Shermans, etc and so on. The X-5-7 variety only requires a 6 lbr or better (57L) to work on from NCA LOS - and you can get those in all kinds of mid to late war AFV's. German AFVs are particularly brutal in cracking open pillboxes, almost every AFV they have in inventory can do in at least a X-3-5 and all big guns can do in any pillbox.
In ASL - the games usually evolve into the "infantry" game and the "armor" game - with winning both required to meet the VC's. If the enemy is not given AFVs to use yours on - use them to fight enemy infantry- particularly the nasty ones in good locations hiding in a pillbox with a .50 Cal HMG and a 9-2 ldr, who is blocking the approach / exit routes, or some such. Pound Mr 9 ML 9-2 / HMG nest with a few 2 flats, you'll get your MC's. Build up the aq on the buddy, and THEN let him have a dose of s# Smoke Ammo in the next PFPh by bracketing to ATT and having the extra -2 TH DRM for the all important smoke shot that blinds him if he didn't break down from the concrete spalling all around him.
Like much else in ASL - timing is everything in the game. Set up the Smoke if you are using it for screening - don't fire it willy nilly just to blind them on turn 1a. use the AP ITT MA for some aq that can be applied to the upcoming Smoke shot, some 2 flat IFT attacks that can and do cause damage to the enemy and the other players PMC's as his pillbox offers no TEM from them, and cautiously move up the close assault team to cover just out of LOS of the pillbox, but within Movement range of a single MPh for that infantry- then use that next PFPh to lay Smoke if needed, and rush the pillbox in the MPh to take it down in the CCPh or with a FT, or waltz up if the 2 flats managed to break the occupants and take the pillbox bloodlessly in the CCPh.
Most will realize a pillbox is a strong defensive addition - but only if placed correctly - A lot fewer players realize they are also turned into death traps in such circumstances - so don't bet the farm on a pillbox with your best SW or ldr in there - if it can be isolated, it will be, and as they do not have to rout, an enemy on top of it in the MPh is enough to prevent the rout altogether, forcing a bloodless CC as you won't surrender either, as you are not required to rout out of a pillbox. (B30.42).