I know it isn't allowed to load more than one round. I've been aware of this from day one. I took Greg's post to say, just like it's written, " Firing rounds from a magazine is against the rules in F class". This could be viewed as multiple or single. Even if you drop the mag after every shot and place a round in it, that's still, firing rounds from a magazine. Which is legal. So, long story short, I didn't want the OP to be lead to believe it's against the rules to "load from a magazine".
Dean is exactly correct. You most certainly can load from a magazine but in High Power competition, with the exception of the rapid fire courses in Service Rifle, only one round in the magazine is allowed.
Now, about this barrel heat thing; the only item that you can use to counteract the barrel heating up too quickly is a heavier barrel. Heavy barrels heat up more slowly than thin barrels, and for the same number of rounds fired in the same time, they will cool faster than thinner barrels because they have a larger surface through which to dissipate heat.
You cannot put a fan beside you to cool be barrel and you cannot use that gadget that was shown earlier; they are in direct contravention of rule 3.18:
"3.18 General—All devices or equipment which may facilitate shooting and which are not mentioned in these rules, or which are contrary to the spirit of these rules and regulations, are forbidden. The Match Director, Official Referee, Jury Chairman or Supervisor shall have the right to examine a shooter’s equipment or apparel. The responsibility shall be upon the competitor to submit questionable equipment and apparel for official inspection and approval in sufficient time prior to the beginning of a match so that it will not inconvenience either the competitor or the official."
Take that to mean that if the item you want to use is not listed in the rules, it's most probably controversial. If you're bringing it to the line because it will make it easier, or provide comfort, or help in any way, it's definitely illegal.
Check out rule 6.3 about using umbrellas and individual covers. Spoiler alert, they're not permitted.