This article is an excerpt from our Sefer
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Removing cartilage from Shofar: 
A Kosher Shofar contains removable cartilage. It is not required to remove this cartilage and even initially it suffices to puncture a hole through the cartilage rather than remove it.
Forming a Shofar from the cartilage: The cartilage that is removed from a Shofar is invalid to be used for blowing even if one punctures a hole through it.
 The reason: Now although the cartilage interferes between the sound and the actual hollow bone which is defined as the Shofar, nevertheless one is not required to remove it as the hollow bone and cartilage are all the same species, and “Min Bemino” does not serve as an interference. Hence it is considered as if there is no cartilage within the Shofar at all. [ibid]
 The reason: The reason for this is because the cartilage is not defined as a Shofar as a Shofar comes from the word Shfoferus which is defined as a tube that is naturally hollow and the cartilage is not naturally hollow. [ibid]