The phrase "more biggun" can be replaced with a number of other words and phrases that convey the same idea of something larger or bigger. Some synonyms for "more biggun" include "larger," "greater," "heavier," "bigger," "bulkier," "more sizable," "more massive," and "more substantial." You could also use idiomatic expressions such as "a whale of a...," "a real behemoth," or "quite a size." Ultimately, the synonym you choose will depend on the context and tone of your writing or speech. By using synonyms for "more biggun," you can vary your language and provide more nuance and detail to your descriptions.