I disagree Twitch - While they may not have been as effective as 2X.5's, they still ripped the tit off many enemy NF's....they could put a fair concentration of lead [of varying compositions] into a coupla square feet of target.
Great Britain had a shortage of armaments approaching the start of WWII, and .5's were hard to get. That's why Hurricanes Spits had 8 - 12 x .303's that definately clawed many Luftwaffe aircraft down in the BoB....While they didn't make much impression on armour-plating, they still tore at everything else that was vulnerable. I'm sure every serving member of the British Armed Forces would've loved heavier calibre, but the .303's sufficed, especially in concert with 20mm cannons in fighters. Any Luftwaffe fighter attacking a British bomber with 4x .303 squirting back would've been ducking, I'm sure I would've.......