I shoot 3 Enfields. One is an Ishapore SMLE MKIII. Apart from a new barrel and new wood it is original The next is a Savage No.4 Mark 1* in near perfect condition and the last is an Envoy in like new condition.
As you will see I use both 7.62x51 in the Envoy and .303 in the others. Here in the UKicon I find that .303 can be purchased cheaper than the 7.62 (.308) It doesn't affect me as in the last 30+ years I have never bought factory ammo (except .22 LR) and the two rounds in question cost the same to reload. I use the same powder type (Hogdon 4895) and weight (43 gns.) in both.
The funny side is when I renew my Firearm Certificate the enquiry office doesn't understand why there are no entries in the Ammunition Purchased section. Peter Laidlericon will know about this. The quality of firearms officers has taken a dive since Peters day.