I join with some of the others in discriminating between the acts of obeying a mad gunman's delusions and martyrdom. A nut with a gun in a church is a man that should be first wrestled to the floor (if possible) and second fled from if he can't be disarmed. But if the true question is "would I deny Christ under compulsion?" I believe (and may be incorrect) the only honest answer is "No." This is not because of my personal integrity, but because of the indwelling of the Holy Spirit. I follow and support the Voice of the Martyrs, and have read a lot of testimonies of people tortured for their relationship with Him.
Peter denied Christ 3 times, yes, but he did not yet have the gift of the Spirit dwelling within him. Now, all those who follow Christ have that gift. I find in the testimonies of martyrs that martyrs are not "special" people embued with miraculous endurance or natural wills of iron. They are "average" people in "special" tribulations, transformed by God through the Holy Spirit and cradled in the arms of His grace.
So my answer, and again, I may be incorrect, is that, yes, as a follower of Christ, consumed and transformed by the Holy Spirit, but not because there is some humanistic "inner strength" which I possess, I would be a martyr.
And so would you.
I think more important than wondering if God would carry us through martyrdom if circumstances so dictate, I believe it is more important that we pray for those who are in chains for Christ at this very moment, for those who suffer right now for their love of God and for those who will not live to see another hour pass because of their adherence to Christ.