Hornady's use of a soft polymer insert in the hollow of the FTX ammo is a great solution to the well documented condition and complaint that JHP's can become clogged with the material they must pass though like heaby clothing and gyp board which can prevent the bullet from expanding as desired. Other companies have developed bullets that will generally perform well through thick clothses, wall board, etc but tests do show that their expansion is reduced somewhat.

I would think that any good pliable and flexible compound would work similarly to Hornady's insert, at least as long as it retained similar characteristics. The problem with calking and other such material you can buy at Home Depot in my experience is that they eventually harden with age and exposure to heat. Horandy's insert likely has a longer usefull shelf life.

As someone once quiped, "the XTP's won>t clog up because they've already been pre-clogged."