A rule of thumb guide for consonant doubling before suffixes is this:
If the last syllable of the root is:
- ends in: consonant vowel consonant
we usually double the final consonant before the suffix. There are some letters that we don't generally double before suffixes. The most important are 'w' and 'y'. The letter 'l' is not one of these letters:
Above we see four words whose roots have stressed final syllables. As they all have a consonant/vowel/consonant ending, the final consonant is doubled. This also occurs with the verb expel in both British and American English.
Note this does not happen with most words if the final syllable is not stressed. In other words if condition (1) is not satisfied:
In the examples above there is no doubling of the final consonant.
However, traditionally, in British English, but not American, we have a rule for doubling double root final 'l'. If condition (2) above applies, whether the syllable is stressed or not, we double final 'l':
[It should be noted, however, that some American style spelling is now an acceptable alternative for some British words. So you can also find 'pummeling' for example in texts using British English.]