Do you notice if the jam is happening on the left or right side? I.e. the mag is double-stack - if you are loading 10 rounds each time you are always starting from the left side (if memory serves me right). If this is the case, take one round out so you are starting with the opposite side. If it does not jam, then the side which does jam on first round needs adjustment. The feeding is always hardest on the first round. I use PPI all the time and have never had issues. Also make sure your mag is seated properly.
Lastly - listen to triplestack and get another Enfield!!!
Lastly - listen to triplestack and get another Enfield!!!