First off, lets not call each other trash or suggest people read a book.
No one's a complete idiot just because they don't know how a Boys AT rifle performs against a Panzer III Ausf F, that's not something I'd consider common knowledge
Second: The Boys AT rifle is unfortunately pretty useless against 'bigger' tanks like a Panzer III. This is a reflection of real life as you can read in the
1942 Boys Training Manual.
When shooting at German tanks of the Pz. Kw. Mk. III and larger tanks, fire should be aimed, if it is possible, at vulnerable points, especially on the junction point of turret and hull and gun mantle to cause burring over of working surfaces and thus produce jamming.
i.e. the manual basically told you that penetration of the tank was unlikely and that your best bet at disabling it was via more 'unorthodox' means.
The Panzer III Ausf F may have had a minimum 10mm of armor, but that was only on the turret top afaik. The rear hull had 20mm of armor sloped at 10 degrees minimum (30 degrees if you're shooting at the lower part), so slightly thicker in practice. Either way, our Boys AT rifle in-game doesn't penetrate the Ausf F because it's unlikely that a penetration would've happened & caused a significant amount of damage to disable the tank in that area with that weapon. FH2 isn't a simulator, but the COL Meshes and damage/ angle modifiers do an okay job of replicating likely outcomes.
The best bet is to use the Boys AT against softer targets and find other ways of attacking the Panzer III, with an AT gun, other tanks, planes etc...