In 8.4, the price for 83mm High-Explosive HE Mk.3 shells will quadruple (already confirmed as 8.4 is live on RU server). Now it costs 85 credit per shell, in 8.4 it will cost 260 silver per shell. Which means if you buy one for 85 now, you can sell it in 8.4 for 130, generating 45 credits of pure income. You can buy shells for guns you don't own in the store.
8.4 will come to EU server on Wednesday (6.3.) and to NA server on Thursday (7.3.) - at least that's the rumor.
Confirmation from RU server: